ulolwe vol 2 issue 9b
DESCRIPTION
The History of the South African Railways,Harbours,Airways and affiliated PoliceTRANSCRIPT
THE ULOLWE
SOUTH AFRICA – SUID-AFRIKA
A monthly railway research / historical publication
‘n Maandelikse spoorweg historiese en navorsing publikasie
Vol 2 no 9B
Un-official / Nie Amptelik Everything to do with the
former South African Railways:
i.e. Stations, Harbours,
Airways, RMT, SAR Police,
Armoured Trains, Lighthouses,
Pipelines, Catering, SAR
Models, Diagrams of
Locomotives etc and books on
the Railways in Southern Africa
Hennie Heymans, Pretoria, South Africa
September 2011
Patron - Les Pivnic - Beskermheer
2
Contents
Foreword by Les Pivnic, South African Railway Historian, on the Paper:
OUR STEAM LOCOMOTIVES by Dr Raimund Loubser ................................... 4
Conclusion ...................................................................................................... 6
OUR STEAM LOCOMOTIVES .............................................................................. 7
1. Introduction ..................................................................................................... 8
1.1 The Motive for Writing this Story .............................................................. 8
1.2 General Comments ..................................................................................... 9
2. The Main ‘Building Blocks’ of the Steam Locomotive ................................... 10
3. Its Historical Development ............................................................................ 11
4. The Main Building Blocks of the Steam Locomotive - A First Approach ....... 13
4.1 The Boiler ................................................................................................ 13
4.2 The Engine of the Locomotive ................................................................. 15
4.3. Auxiliaries .............................................................................................. 16
5. The Boiler and its Accessories ...................................................................... 16
5.1 General .................................................................................................... 16
5.2 Boiler Efficiency .................................................................................. 16
5.3 Boiler Efficiency - Cls 26 ..................................................................... 19
5.4 Boiler Maintenance .............................................................................. 20
5.5 Smokebox ............................................................................................ 21
5.6 Safety and Other Ancillaries .................................................................... 22
5.7 Keeping the Boiler Clean Inside ........................................................... 26
6 The Engine of the Locomotive ...................................................................... 27
6.1 Reciprocating vs. Turbine Engines........................................................ 27
6.2 Pistons and Cylinders (Fig 30) .............................................................. 28
6.3 Rods ..................................................................................................... 29
6.4 Coupled Wheels ................................................................................... 31
6.5 The Control of the Steam ...................................................................... 33
6.6 Frame, Suspension and Curve Handling ................................................... 38
6.7 Lubrication ........................................................................................... 42
6.8 Tender .................................................................................................. 42
6.9 Vacuum Brakes .................................................................................... 44
7. Problem Solving for the Railways - Personal Experiences ........................... 45
7.1 The Case of the Fractures of the Unbreakable Connecting Rods ............ 46
7.2 Case II: The Fractured Blower Turbine Blades ..................................... 49
7.3 Rails ..................................................................................................... 52
7.4 Dynamometer Tests on the Narrow Gauge Railway ............................... 55
Appendix A ........................................................................................................ 56
Locomotive and Tender Numbering Systems .................................................. 56
Appendix B ......................................................................................................... 57
Eleven Representative SAR Locomotives ................................................. 57
19 and 19d ..................................................................................................... 57
S1 Shunter ..................................................................................................... 57
24 .................................................................................................................. 58
16E ................................................................................................................ 58
15F ................................................................................................................ 58
23 .................................................................................................................. 59
GMAM .......................................................................................................... 59
3
25 .................................................................................................................. 60
26 .................................................................................................................. 60
The Final Verdict ........................................................................................... 61
B7 ..................................................................................................................... 63
Table B1 - Locomotive Power Data ............................................................... 63
Table B2 - Locomotive Performance Comparisons ...................................... 64
Appendix 1 ......................................................................................................... 66
Summary of Robin Barker’s View of the Origin of the 4’-8½” Rail Gauge .... 66
Figures .............................................................................................................. 67
FIG 1 & 2 ...................................................................................................... 67
FIG 3 & 4 ...................................................................................................... 69
FIG 5 & 6 ...................................................................................................... 70
FIG 7 & 8 ...................................................................................................... 71
FIG 9 ............................................................................................................. 72
FIG 10 – Class 25 & 25NC (1953 – 1955) ...................................................... 73
Fig 11 ............................................................................................................ 73
Fig 12 Local & USA Mallets .......................................................................... 75
Fig 13 ............................................................................................................ 76
Fig 14 ............................................................................................................ 76
Fig 15 & 16 ................................................................................................... 77
Fig 17 ............................................................................................................ 78
Fig 18 ............................................................................................................ 78
Fig 19 ............................................................................................................ 79
Fig 20 ............................................................................................................ 79
Fig 21 ............................................................................................................ 80
Fig 22 ............................................................................................................ 80
Fig 23 ............................................................................................................ 81
Fig 24 Cab of GMAM 4051 ........................................................................... 81
Fig 25 ............................................................................................................ 83
Fig 26 ............................................................................................................ 84
Fig 27 ............................................................................................................ 84
Fig 28 ............................................................................................................ 85
Fig 29 ............................................................................................................ 85
Fig 30 ............................................................................................................ 86
Fig 31 ............................................................................................................ 87
Fig 32 ............................................................................................................ 88
Fig 33 Loss of White Metal after Overheating ............................................... 88
Fig 34 & 35 ................................................................................................... 89
Fig 36 & 37 ................................................................................................... 90
Fig 38 – Model of a Walschaert Valve Gear ................................................... 91
Fig 38 - Settings ............................................................................................ 91
Fig 39 ............................................................................................................ 92
Fig 40 & 41 ................................................................................................... 93
Fig 42 ............................................................................................................ 94
Fig 43 ............................................................................................................ 95
Fig 44 ............................................................................................................ 96
Fig 45: Class 25 Overlubricated ..................................................................... 97
Fig 46 ............................................................................................................ 97
4
Fig 47 ............................................................................................................ 98
Fig 48 ............................................................................................................ 98
Fig 49 ............................................................................................................ 99
Fig 50 ............................................................................................................ 99
Fig 51 .......................................................................................................... 100
Fig 52 .......................................................................................................... 101
Fig 53 .......................................................................................................... 101
Fig 54 .......................................................................................................... 102
Fig 55 ......................................................................................................... 103
Fig 56a ........................................................................................................ 103
Fig 56b ........................................................................................................ 103
Fig 57 .......................................................................................................... 104
Fig 58 .......................................................................................................... 104
Steamloco Images ........................................................................................... 105
Photographs .................................................................................................. 107
Foreword by Les Pivnic, South African Railway Historian, on
the Paper: OUR STEAM LOCOMOTIVES by Dr Raimund
Loubser
I would like to compliment Dr. R. Loubser for producing a really excellent Paper -
most informative and written in a lovely informal style that should be enjoyed by
the lay-reader and professional alike.
The incident about watching a family of cheetahs clear the line in front of a class 24
in the KNP with the Author observing this from the loco's front buffer beam, bears
witness to this!
The Author's work in finding the Henschel fault - having to rectify faulty milling
and the unacceptable work done to rectify the problem - was brilliant to say the
least!
On page 271:
First paragraph - last sentence:
Dr Loubser says:-
....but the engines were converted back to the 1930/50 design after only a short
period of service - and I don't know why.
In answer to that question, I am quoting an item here that appeared recently in the
SAR-L chat line and it reads:-
1 Now page 31 - HBH
5
"Both condensers and the others (25 and 25NC) were initially built with alligator
crossheads except for 5 x 25's that experimentally had the multi ledge slidebar.
From conversations with people that were intimately involved with the
maintenance of these locos I learnt that the motion girder of the alligator crosshead
was very prone to cracking and this could not be solved. Having recently looked at
the drawing of this motion girder I am not that surprised. Thus from 1959 onwards
the multi ledge slidebar and its simpler and stronger motion girder became the
preferred arrangement. In any case, as an example of American mechanical design
it is not very difficult to see how it is superior and in fact most of the mechanical
design of the 25/25NC is contemporary (1940's) American practice."
The item continues and I am sure that the Doctor would be interested in the
balance, which is as follows:-
In response to the statement from Andre that tests with the Class 20 persuaded
Grubb to proceed with the Class 25, this is certainly not true. Grubb and his
department had severe reservations about the mass ordering of these locomotives.
From many conversations with the late Murray Franz, who was part of the Test
and Design section at the time of the Laingsburg boiler tests, and who knew many
of the people who were intimately involved in the gestation of the design of the
25/GMAM classes (which proceeded more or less in parallel) it is clear that the 25's
(condensers) were a result of a clear directive from the GM's office. I have a copy
of a letter from Grubb to the GM which clearly states that this was the reason for
the designation of 25NC (or alternatively the suggestion of 25N) and is a result of
Grubb's supposition that many variants of the 25's would be necessary in
subsequent modifications to make a successful class. In fact Franz told me that
Grubb had told the GM that, if it was their wish that the 25's were delivered en
masse, that they (the CME's department) would do their best to make them work.
There is good evidence to suggest that the huge problems with these locomotives
was instrumental in early opinion for turning the SAR away from steam, especially
with the very successful dieselisation of SWA just a few years away, almost
contemporary and almost certainly gestating during the period when the problems
with the 25's were a running sore in the late 1950's. Notwithstanding the fact that
the effort in solving these problems resulted in the 25's being a hugely successful
class, the cost of maintaining the condensing tenders was large and with the
electrification of the Karoo the need for them was lost, even though use for them
was found for them elsewhere. In terms of overall cost, a condensing tender cost as
much to overhaul as the locomotive itself However, as a tribute to American
mechanical sophistication a 25NC cost just 50& of its cousins of more basic design
(15F, 23, etc) in mechanical maintenance.
End quote.
Page 54:2
2 Now page 59 - HBH
6
Class 16E:
Dr Loubser refers to the 16Es being sadly relegated to minor duties after being
withdrawn from "Blue Train" service.
If I may, I would like to offer a correction in this regard.
These locos were built to haul the Union Limited and Union Express (fore-runners
of the Blue Train) and were placed in service in 1935, stationed at the old
Kimberley Loco opposite the Station. They worked the Expresses north to
Johannesburg and south to Beaufort West.
In 1939 when those trains were equipped with steel-bodied air-conditioned stock,
it was considered that the 16E might not be able to re-start the train on a grade if
brought to a stand at a signal. For this reason, class 23 locos were used in place of
the 16Es and wide-firebox 16DAs that had been in use previously. All the 16DAs
and 16Es were then transferred to Bloemfontein loco, from where they continued
to work fast main line passenger trains including the Orange Express from 1947.
Even when the Orange Express was re-equipped with steel coaches (C-34 and E-
16), the 16DAs and 16Es continued to work that train between Bloemfontein and
Kimberley.
It was only in the final years of service that the 16Es were relegated to minor
duties before being withdrawn from service in 1972.
Conclusion
Overall, the Paper is a wonderful document that goes a long way to explain the
inner facets of locomotive design and operation.
The descriptions of the tests conducted on a 3B boiler on a class 23; the tests on
class 25 connecting rods and the smokebox turbine blades, make for totally
fascinating reading for anyone with an interest in the SAR steam locomotive.
Yours sincerely
HL Pivnic
P.S. I would be in a position to provide photographs of all the locomotives under
discussion should they be required.
This would be possible towards the end of this year due to the fact that
unfortunately, with my emigration to Australia, my SAR material is presently not
accessible.
7
OUR STEAM LOCOMOTIVES
The simple but ingenious devices and
design principles that made them work well
- most of the time!
by
Raimund Loubser
TEXT
Ter herinnering aan my Pa
Thys (“MM”) Loubser
Die skepper en vriend van
goeie lokomotiewe
Jammer, Pa, dat die teks nie in Afrikaans is nie!
Dedicated to the many innovators who
solved the problems of the emerging steam locomotive,
the designers, workshop staff and those on the footplates
who made them run well,
and
their poor wives who had to keep the loco home fires
burning while their hubbies were playing with their trains.
August 2005
Improved June 2009
8
1. Introduction
1.1 The Motive for Writing this Story
The author offers the following information on his background which induced him
to write up something about steam locomotives - after all, they are no longer
relevant in today’s world. They remain, however, very much of interest to me as
they are so intimately associated with our family history. My father Thys ( MM )
Loubser spent most of his career in the then SA Railways, my brother Kobus
(JGH) his full business life, and myself the first five years as engineer, all of us
involved with steam locomotives in one way or another. It also appeals to me that
the steam locomotive, in spite of its noise, dirt and inefficiency compared to diesel
locomotives and electric units, kept going for a half a century before they were
supplanted by the latter. What helped them to survive are the simple but effective
concepts and component design features that were adopted in the first century of
their existence which made them good performers (well, most of the time!) I would
like to share this with you.
To elaborate on the family background, my father Thys already wanted to become
a railway engineer as a teenager. After gaining his B-degree at Victoria College
(now Univ. Stellenbosch) in 1910, he went to the Technische Hochschule
Charlottenburg, Berlin, where he got his Diplomingenieur in railway engineering in
1914, unfortunately after the War had already begun. (This Diplom has been
evaluated as one year more advanced than the local B Sc Eng). He returned to
South Africa in 1919 but had to wait until 1925 before he could get an appointment
in the SAR, as the first Test Engineer in the Mechanical Dept. He commissioned the
new Dynamometer Coach (Coach 60)3 and in 1926 submitted his design for the
Class 19* Locomotive to the then Chief Mechanical Engineer (CME), Col Collins.
“MM” was Chief Mechanical Engineer from 1939 to 1949, during which time he
introduced several further innovations in the locomotives he designed. See
Appendix B for some details of these and a few other locomotives introduced
mainly in the period 1925 to 1955.
During this time my brother Kobus was mainly involved in establishing improved
manufacturing processes in the SAR Workshops, which reduced maintenance costs
and improved locomotive reliability. By the time he became CME, steam
locomotives were on their way out.
Raimund learnt a lot from his Dad, such as his experiences with the correct design
of blast caps on Garratt locomotives which were notoriously bad steamers (See
Section 5 on Boilers). He attained his B Sc, B Sc Ing (Werkt) at Stellenbosch, and
3 Photo of coach no 60 supplied by Les Pivnic - HBH
* See Appendix A for Locomotive and Tender - Class and Numbering Systems. The other
Appendices make good reading at this stage if you are not familiar with locomotives.
9
joined the SAR as Pupil Engineer in Jan 1949. He resigned in 1954 to become
Research Officer at the CSIR’s National Mechanical Engineering Research Institute
(NMERI), Strength of Materials Section. He left the CSIR in 1964 for Pelindaba.
His experiences in the SAR included the Mechanical Workshops in Pretoria, boiler
efficiency improvement tests on the Cls 23 (Cls = class) at Laingsburg which led to
the improved boiler for the Cls 25/25NC*. He took part in traffic tests using the
Dynamometer Coach and introduced the new Cls 24 to the (long defunct) Selati
line for hauling Palaborwa ore exports. His last job was accepting the first GMAM
(4051) on behalf of the Northern Transvaal System. This included a hair-raising
run up the bank from Waterval Onder to Boven - see Appendix B. While at the
CSIR, investigations were carried out at the request of the SAR. These included
fatigue tests on rails, solving the early failures of Cls 25NC connecting rods, and
fatigue failures of blower turbine blades on the new Cls 25. For the PPC Company,
traffic tests were carried out on the narrow gauge line to Port Elizabeth. No
narrow gauge dynamometer coach was available, improvised measuring practices
were used.
1.2 General Comments
• The old British units of measurement were retained. All SAR steam locomotives
were designed and built before metrication in 1961, therefore all original
drawings and instruction booklets use feet & inches; tons, cwt & lbs; miles per
hour, etc. So these have been used here, with only a few comparisons with
metric units to assist in understanding for the younger generation. ‘lb’ is used
even for lbs force, not lbf.
10
• The use of tons, however, remains confusing, as a ton of 2000 lb was also
commonly used in this country. It was used in the SAR for coal and train loads.
Axle loads were however given in British long tons of 2240 lb and in
hundredweights (cwt) of 112 lb. (This ton is practically the same as the metric
ton of 1000kg or 2204 lb.) This practice has been retained in these notes.
• The drawings of locomotives in Appendix B were copied from Holland’s book
(Ref 3). They were, in turn, redrawn from the original SAR Locomotive Index.
The SAR peculiarities were retained, eg boiler pressure as abbreviated to “200
lbs” instead of “200 lb/sq in”.
• Locomotives of the SAR were designed locally in broad terms, but standard
components were specified in full detail using the drawings issued to the SAR
Workshops for the manufacture of spares. New locos were all imported in a
semi-complete form and assembled in the SAR Workshops. Detail drawings
had to be supplied by the manufacturer and the SAR retained the right to copy
these drawings and to manufacture any component for their own use, or to
specify that particular design in any further orders for locomotives. The main
exception to loco supplies from overseas was the first batch of the Cls S1
shunter which was built in the Salt River Workshops towards the end of World
War II.
• “MM” was the driving force to ensure that all steam locomotive drawings were
completely bilingual, in English and Afrikaans. Afrikaans terms were created
as needed and issued in dictionaries, copies of which I have.
2. The Main ‘Building Blocks’ of the Steam Locomotive
What is a Steam Locomotive?
The term Locomotion is derived from old French, meaning to move from place to
place, based on the Latin loco + motivus.(Ref McGraw-Hill’s Heritage Dictionary)
For practical purposes, a Steam Locomotive is a traction machine, moving (we would
now use the term running) on a rail track, capable of hauling a load of coaches or
trucks weighing several times as much as the locomotive. It carries its own supplies
of coal and water which are used to generate steam, the latter being the source of
power to drive the engine of the locomotive. This develops the Tractive Force to
haul the load.
The locomotive functions are best dealt with in three parts, ie the Boiler, in which
the coal is burnt to produce the steam at high pressure and temperature, the
Engine, which converts the energy contained in the steam to traction power, and
the Tender, the storage unit for the coal and water. There is considerable
interaction between these three, which will be dealt with. In the case of Garratt
locomotives, however, there is no tender, the coal and some of the water is carried
on the engine as such. Extra water is usually drawn from an auxiliary tank car.
11
At this stage it would be convenient to start with a brief history of the steam
locomotive.
3. Its Historical Development
The start of the locomotive is really based on the availability of some form of
railroad. This takes us back to the Roman roads of about 2000 years ago, solidly
built using stone laid in mortar some 16’ broad. There were paved roads even
earlier in the Middle East, but it was the Romans with their organising ability that
went so far as to lay down standards for the breadth of the roads and the wheel
spacing of about 5’ outside to outside, which comfortably made do for a one horse
chariot or cart . A case has been made (Ref 10) that the ruts that have been found
in some of these strips (we found none on the roads left in England), were cut to
guide the wheels, but I have my doubts. There is a case that the ruts were caused
by wear - those I have seen at Pompeii could have been. Intentionally cutting
them in, meant that it would have been very difficult on the roads to pass each
other. However, the important point is that a method was developed for the easier
movement of loads, ie Locomotion! The Roman principles used can be
summarised as follows: a) use a solid smooth carriageway; b) lay them on a solid
foundation; c) standardise the wheel spacing (the Gauge as we call it) and d) keep
gradients to a reasonably low value so that your horse (or locomotive) can haul a
fair load of one or more vehicles at a fair speed.
This discipline was lost for many centuries and the unmade Elizabethan roads
were marshes at times. But the advent of coal mining in those times led to a start
of wooden strip roads, at first in the mines, then to the nearest port. It helped if the
wooden strips were laid to a standard gauge to suit a wheel spacing that could
accommodate a horse- the restart of the 5’ outside gauge in about 1650! About
1740, cast iron wheels were introduced, and shortly afterwards it became practical
to cast iron strips with ridges, to be used as rails fixed on top of the wooden strips.
(See Appendix 1 for more exact details) At first they broke under the iron wheels
of the heavy trucks: the trucks were made smaller and a train of several trucks was
used. Eventually the problem was solved when the art of casting malleable iron
was developed (1805). The first railway was there and now a horse could haul a
few trucks with many tons of coal out of the mine to the nearest port, canal or
navigable river, on its way to towns and the nearest new industries.
When Watt’s stationary steam engines was built in the 1770’s, it showed the way to
develop a successor to the horse. The Cornishman Trevithick took the lead: he
first worked on steam road vehicles, but when one of them capsized on the muddy
English roads and badly injured him, he turned to rail locomotives for collieries.
The first one opened a new age around 1804, just over two centuries ago. It is well
known that Stephenson, also a Cornishman, built the first really effective rail
locomotive, the Locomotion, for the Stockton and Darlington Railway in 1825. It
hauled a load of 90 tons: 38 (!) wagons and coaches at a speed of average 10, max
15 mph. The Locomotion already had two coupled driving wheel pairs and his 1845
12
model the Derwent, three. His Rocket, which won the 1829 ‘Rainhills’ Competition
by reaching 30 mph, had only one driven wheel pair (configuration therefore 0-2-
2).
The important innovations that Stephenson introduced or developed, were
• Most important, developing Trevithick’s idea of blowing the exhaust steam up
the chimney, to the point where the draft it created in the fire produced just the
right amount of steam in the boiler to maintain that power output. It worked
adequately over a wide power range.
• The 4’-8½” rail gauge, on wheels with inner flanges. Proper ‘rails’ were used,
not ruts in a strip.
• A long chimney, topping at about 12 ft above rail level. It helped to keep smoke
out of the driver’s and passengers’ eyes, but more important for the future, it
opened up the concept of a large loading gauge (Fig 13).
• A double eccentric driven valve gear (It controls the steam entrance to and
exhaust from the cylinders) which easily allowed the driver to smoothly adjust
the cut-off (power level) and to change into reverse with a single control lever.
When the railways came into being in this country, it remained the main choice
for valve gear until about 1910.
• Addressing the complaints of the “Greens” of those days. Smoke! Coke making
had just been invented, and he promptly used coke on the Rocket run. It may
have helped to win the day, but it seems that its use was stopped when the bills
for the coke started to mount up. What is new?
Other innovations that were introduced during the first century of locomotion
were:
• Superheating of the steam, which only slowly found its way into the local
standards as from 1904. Superheating reduces the risk of water in the cylinders
which can lead to severe failures; it also improves power and efficiency.
• Walschaert’s valve gear, which he invented in 1844 in Belgium. It was soon
adopted in Europe, but was not favoured in the British tradition and only found
its well-deserved way into our country when the Dutch of the ZASM introduced
it on their ‘46-tonner’ in 1892. It gradually became our standard valve gear. It
has big advantages over Stephenson’s gear in that the valve can be given a
longer stroke and that the gear is accessible on the outside of the engine.
In South Africa, the building of railroads started around 1860 in the Durban and
Cape areas, British engineers and developers being the main initiators. The initial
choice of gauge for the Cape - Wellington line was therefore 4’-8½” as in England.
When the problems and costs of building lines through our passes became clear
(even before the Hex River pass was planned), it was decided to fix the rail gauge
for all new lines at 3’-6” (42” = 1067mm, as also used in Norway, Queensland,
Tasmania and in pre-WWII Japan) and to convert already built lines to the same
gauge. What proved a big advantage was that the big Loading Gauge was retained,
as the platforms etc, were already built for the broader gauge. Fig 13 shows the
comparison between the local, British and USA rail and loading gauges.
Obviously the USA can build far bigger and stronger engines such as ‘Big Boy’.
13
We and the UK have the same smaller potential. One difference is the rail gauge:
we can build track with a 26% smaller minimum radius. It would not have been
practical to use the pre-1980 route up the Hex River Pass with a broader gauge. On
the other hand, our maximum allowable speeds must be less than in the UK, the
bigger overhang leading to a lower stability.
The use of the narrower gauge also meant that there is more room on the outside
of a locomotive frame which makes larger diameter outside cylinders possible -
24” diameter in practice. Even then, we are at a practical limit. Steam pressures up
to 225 lb/sq in. have to be used to obtain the reasonable maximum tractive effort
we need on a 4-coupled engine like the Cls 25 with only 5’-0” d. wheels. There is
not sufficient room for cylinders and their valve gear between the frames. The
proof of the pudding lies in the Cls 16A and 18, which were retired early as they
gave far too many problems with their inside cylinder(s) and valve gear.
A reasonable summary of the SAR steam locomotive history from about 1925 can
be made by looking at what happened to eleven of the classes up to 1955, when the
last of the new locos of the Cls 25 were delivered. One further class is dealt with,
the conversion of one of the Cls 25NC to the ‘experimental’ Cls 26. These are
summarised in Appendix B. Their data relevant to their power outputs have been
tabled in Table B1 together with that of a comparable Electric Unit and two Diesel
classes. From this data, the Load capacity and Horsepower of the Cls 25NC and 26
are compared with that of the Electric Cls 6E1 and the Diesel class 34, to give some
insight as to why steam locomotives became museum pieces about 1990.
4. The Main Building Blocks of the Steam Locomotive - A First
Approach
Reverting to the Main Building Blocks of the steam locomotive, it was thought
prudent to give a summary of what will be dealt with in more detail later. It will
also help to get used to the language that is commonly used!
4.1 The Boiler
With reference to Fig 14, which is a diagrammatic ‘cut-through’ sketch of a boiler
of about a 19D vintage, the boiler has three basic sections: starting on the right, is
the Firebox, which includes the Grate at its lowest level; the Boiler barrel is in the
centre, and the Smokebox is attached to its left (front) end.
Firebox: The firebox top, the Crown Plate (B), is flattened to fit under the water
level at the barrel top. Along its sides and end there is a water space of about
6”(R). The whole box is prevented from imploding from the high boiler pressure,
by a forest of anchors called boiler stays (not shown on the drawing) fitted from the
outer shell of the boiler to the firebox inner wall(C) and the crown plate. The
entrances to the firebox are through the Firebox Door (stookgat) at the far right
where the coal is shovelled in, and the grate at the bottom where the coal burns
with the air drawn through the grate. The outlet of the firebox is through the
14
multitude of Boiler Tubes (G) welded into the firebox Tubeplate (A) at the left of the
firebox drawing. The firebox houses a Firearch (Q) of bricks supported by Syphon-
or Archtubes running from the lower back wall up to the higher part of back wall
(C). Water circulating through these tubes keeps them from overheating and adds
to the steam production
Boiler Barrel: The Boiler Tubes (G) are in the lower two-thirds of the barrel and the
bigger Superheater tubes (F) in the higher part. The top, however, is kept clear to
have room for water to cover the crown plate and tubes by at least 6” and to have
still more room above the water level to contain the steam under pressure. On the
top of the boiler is fixed the dome (H) from where the steam is collected. Close to
the dome are the safety valves which release steam to the atmosphere if the
pressure exceeds the prescribed boiler pressure.
Smokebox: As far as steam supply is concerned, the smokebox contains the
Superheater header (K) which draws Saturated Steam from the dome through the
Main Steam Feedpipe (J). The header supplies the steam to the Superheater Elements
(L) and on the superheated steam’s return, feeds it down to the cylinder valves
(not shown).
Exhaust steam from the cylinders is piped to the Blast Cap (M) where it blows with
the smoke through the Chimney (N) to the atmosphere, creating a partial vacuum in
the smokebox. This creates the fire grate draft which keeps the fire going. The
harder the blast, the bigger the draft and the coal burning rate. The steam
production rate can be made to match the steam demand rate by design of the
correct blast cap and chimney size. The Spark Arrestor (not shown) fits around the
blast pipe and chimney; it will be dealt with later in section 5.5.
Entrance to the smokebox is through the Smokebox Door (O) at far left. It is screwed
closed and needs to be airtight to maintain the partial vacuum when steaming.
A general summary of how the boiler works is as follows: A ‘new’ boiler will first
need to be filled with water by hose, up to the level shown in Fig 14. Hot water is
used in the running shed to cut the time to reach full boiler pressure to about an
hour; with cold water it needs three hours or more. About 4000 gallons of water
are needed to fill a big boiler. To get the fire going, burning coal is brought in
wheelbarrows to the cab and handed up shovel by shovel to the stoker who throws
it in through the opened fire door onto the grate. Just imagine the heat, smoke and
sweat involved for those men - one to two tons of burning coal is needed! To
speed up the fire, air needs to be forced through the fire grate. Around the blast
cap in the smokebox is an annular blower with holes pointing up into the chimney.
As it blows, it pulls enough air through the fire grate. Compressed air can be fed to
it by a pipe entering from the outside of the smokebox. Loco sheds always have
compressed air on tap and that is used until the steam pressure reaches about 30
lb/sq in, when the locomotive’s own boiler can supply the blower with steam.
Shortly after that, a mechanical stoker can also take over from the hand shovel and
15
then normal working carries on. This includes using the steam-fed Injector
(Section 5.6.5) to pump water from the tender into the boiler as needed. Boiler
pressures depend on the loco class, but they are all around 200 lb/sq in - enough to
push a column of water (say, in a pipe) 450’ up to reach the top of a 45 storey
building. The load pushing the crown plate of the firebox down in the case of the
cls 23 boiler is almost 1000 tons at normal boiler pressure, so stand well clear the
next time you come across a working steam loco!
When the locomotive has to start pulling a train, the driver opens the Regulator in
the header (K), and the saturated (wet) steam, still at the boiling water
temperature of about 2000 C, rushes through the very hot superheater elements,
emerging as superheated steam of at least 3000 C (Ouch - it will melt tin!) on its
way to the cylinders. It is still at full boiler pressure. This steam is transparent; if
it leaks outside the boiler, you see nothing until it has blown a foot or so away -
only then does the white cloud start forming. Again, keep well away.
Heat from the fire is conducted to the water in the boiler through the steel walls of
the firebox and the pipe walls of the arch tubes, then through the boiler and
superheater tubes, the smoke emerging into the smokebox with most of its heat
transferred to the water and superheated steam. Unfortunately it also carries with
it unburnt coal and char, causing black smoke. The harder the boiler works, the
faster the air is drawn through the grate and the bigger are the char and smoke
losses. Steps to reduce these losses are dealt with in Section 5.
4.2 The Engine of the Locomotive
In this part of the locomotive, the energy available in the hot, high pressure steam is
converted into kinetic (in common terms, moving) energy by forcing the pistons
backwards and forwards in the cylinders. In the process it losses most of its pressure
and cools down considerably; there is a pressure of a few lbs/sq in. left to create
the blast in the smokebox from the blast cap to the chimney, drawing the smoke
with it. (As I am writing this rough draft, we are sitting on the beach at Victoria
Bay, and the ‘Outeniqua Choo-Choo’ is passing us on its last lap to George. It is
being drawn by a splendidly renovated 19D with a ‘Perdeby’ tender (Fig 2) and
steaming well. (Baie dankie, Pa Thys!)
The backwards-and-forwards (The engineers would say reciprocating) motion of
the pistons is converted into a powerful rotational force at the driving wheels
through the connecting rods and then the coupling rods Thank you, Mr Stephenson,
for your simple but effective idea. More about this and the not-so-simple valve gear
which controls the inlet, expansion and exhaust of the steam in the cylinders, will
follow in Section 6.
The Engine part of the locomotive is mainly made up of the loco Main Frame, the
wheel system and the cylinders; it forms only a fraction of the locomotive and
tender. In an Electric Unit nearly all of it is dedicated to power output, its
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equivalent to the steam locomotive’s tender and boiler being little more than the
pantographs on the roof and the limited control gear, provided of course that the
overhead power line is doing its job. Steam cylinders are a bit more compact than
electric motors for a given power output, but in the end Electric Units are only
about half the size of their steam equivalents (Appendix B, Table B2).
4.3. Auxiliaries
These include the tender with its Mechanical Stoker and Brake Systems, they will be
dealt with in Section 6.8 & 6.9.
5. The Boiler and its Accessories
5.1 General
An unusual approach will be followed in discussing the details of the boiler, ie to
deal with them from a) the boiler efficiency and then b) the boiler maintenance
point of view. This will automatically lead to the what and why’s in the design and
constructional details. It should also be pointed out that in the period up to 1955,
we engineers still did not have the capabilities to design a boiler in detail from
first principles, either from the heat generation and transfer (thermodynamics), or
from the strength point of view - computers were not yet there. So designs were
based largely on experience gained from available locomotives and tests done on
them. Intelligent intuition played its role: as my brother’s favourite and respected
practical team member, Les Mitchell, used to say, “A good guess is better than a
bad calculation”. I agree!
5.2 Boiler Efficiency
By 1949 it became clear that more main line steam locomotives would have to be
ordered within the next three years or so. It was also felt that a more effective,
lower maintenance and more powerful boiler than the existing Std. 3B boiler was
desperately needed for the new loco. All locomotives with a Std 3 boiler had
trouble with a fire that was more intense in some parts than the other, contributing
to ‘drawn fires’ at high stoking rates. The burning coal layer is broken up by the
draft and vibration, some being thrown into other parts of the grate, leaving open
grate pockets. The cold incoming air concentrates in the open areas, the burning
rate in the rest goes down and of course so does the steaming rate. The fire is not
easily restarted in the open parts and the loco fails in section (ie between stations)
for a quarter of an hour or more. Also char loss became high and therefore boiler
efficiency fairly low. (Maintenance problems will be dealt with in Section 5.4).
The CME’s Test Section was therefore called on by “MM”, just before he retired, to
get going with boiler efficiency tests on a 3B boiler and to try to improve the
design. They needed more staff and Raimund, who was one of the fledgling Pupil
Engineers (Don’t ask me what we were called behind our backs in Afrikaans!) was
called up from the Workshops training session and transferred to the Test Section,
in the middle of 1949, in anticipation of these and traffic tests. We were going to
17
use the old Dynamometer Coach (Coach No 60, Fig 15) which can measure and
record on a large roll of paper, the drawbar pull where the coach is coupled to the
tender, as well as the speed and boiler pressures, etc on the locomotive. In
anticipation of the boiler tests, Raimund was also instructed to design and build
measuring equipment to measure the steam consumption of the mechanical stoker
(of course it was powered by a small two-cylinder steam engine!) that would be
used on the Cls 23 loco, No 3211, allocated to the tests, as well as the pressure
below atmosphere under the grate, in the firebox and the smokebox etc. ‘Keep it
simple, and remember it will be bolted to the end of the tender in the open and
subject to plenty of bumps and vibration!’ (Fig 16) ‘Also start thinking of how we
can estimate the steam loss if the safety valve(s) blow - there is no way that it can
be measured directly’.
Maybe we should stop a bit and explain what is meant by boiler efficiency. In
simple terms it is the ratio of the extra energy in the superheated steam fed to the
cylinders over and above that of the cold tender water fed to the boiler, compared
to the heat value contained in the coal stoked (or burnt) during the same time. We
accepted that the heat value is that determined by ideal combustion of the coal -
we left it to the coal suppliers to calculate that from the coal analysis. To make
practical sense of these values, they have to be related to the efficiency with which
the engine part works, which means that the tests must be carried out with the
loco hauling a load, so that a power determination can be made from the drawbar
pull, the speed and the known weights of the locomotive and the load.
The next factor to be taken into consideration is the known fact that both boiler
efficiency as well as engine efficiency vary with power level, so that an assessment
of how well the boiler (and engine, in a different way) performs, must be done
over a wide power range. Moreover, it is difficult to keep the test conditions
constant and to ensure that the inevitable variations between the beginning and
end conditions of the test run do not significantly influence the test results. After
all, if you start a test with, say one ton of coal on the grate, how much more or less
coal do you estimate there is by the end? And how much more or less is it burnt?
It helps if you have a long run with a constant uphill gradient which will consume
a few tons of coal, carefully measured, and then to use a practiced eye to estimate
the start and finish condition of the fire. The best place available was the run from
Laingsburg to Pietermeintjies, with an average gradient of 1 in 66 all the way
except through the sidings and stations. It worked well to warm up the loco by
running the load at the required rate to one of the first stations, stop and quickly
measure the water level in the tender and estimate the fire condition, then rapidly
get the train up to the test power rate and keep it constant right up to
Pietermeintjies, then repeat the water level readings to give the total water
consumption which is equal to the steam output. The latter needed corrections for
the stoker and safety valve losses. Now how do you keep the power output
constant? Simple, if you know how - attach a small pipe to the blast pipe, and run
it to a pressure gauge placed in front of the driver. He is told to run the engine so
that the blast pressure remains constant at, say, 6 lb/sq in. As the train picks up
18
speed through the level track of a station, he reduces the cut-off on the valve gear
(See Section 6) correspondingly to keep the blast pipe pressure constant, opening
up gradually as the train starts climbing again and loses speed. A constant blast
cap pressure leads to a constant draft through the fire. If the stoker keeps the fire
thickness constant, we have a constant coal consumption ie Firing Rate, which is
what we need. But how do we measure the coal consumption? The Civil
Engineering Section built a mini coal loading platform next to a siding at
Laingsburg. A supervised gang of labourers filled sacks of coal, each with exactly
50 lbs of coal, and a few tons of these were loaded onto the tender each morning
for the two trips planned for the day. There was severe competition not to get the
job of sitting in the tender amongst the muck and dust to count the number of
sacks dumped into the conveyer screw during the test proper and to estimate the
fraction of a sack not used!.
Measuring the steam loss when the safety valve(s) blow was a problem. The best
we could do was to place 3211 stationary on a flat track and close the injector. The
fireman opened the (smokebox) blower while two of us kept check on the water
level in the boiler. When a safety valve opened, the fireman closed the blower
valve and a stopwatch was started to measure the duration of the blow. At the end
of the blow, the stopwatch clicked and we watched the boiler water level until it
stabilised. We then took the water level reading. From the drawing of the boiler
we could calculate the amount of boiling water that had been used up, which was
taken as the steam loss. A first snag was that as the safety valve opened, the
sudden release of the steam led to increased ‘bubbling’ of the boiler water and an
increase in the water level shown in the gauge. After the valve closed, the water
level shown kept dropping for a while before settling down again. How long
should one wait to reach the same condition as before the safety valve opened?
The next snag was that one could hear that the blow was harder if the steaming
rate was higher. So we had to repeat the test over the whole range of firing rates.
Anyway, we could get a reasonable guestimate of the steam loss from a safety valve
blow, but also got the fireman to understand that blowing safety valves were ‘not
on’ during the test run.
After one half day had been spent on such a test trip and all had gone well, we
would have only one point on the graph of boiler efficiency vs firing rate after an
evening’s calculations - and we needed at least six such points spread over the
whole practical firing range, to have data which could be used for comparisons
between different designs of the boiler.
The boiler efficiency graphs for the 3B boiler before and after the ‘best’ alterations
are given in Fig 17 (Ref 1). One rather disconcerting graph is included, ie the
efficiency achieved by hand-firing 3211 with most of the improvements tested: It is
far better than any of the others, in fact calculations show that the same steam
production could be achieved by hand-firing at 145 lb/sq ft than by mechanically stoking at
180 lb/sq ft! The latter needs to crush the coal in the feed screws to enable the
steam jets to blow the coal into the firebox. The fine bits of coal are easily lifted
19
from the grate by the air entering from the ash pan and are blown out of the
chimney, largely unburnt, hence the lower efficiencies. In hindsight, it is strange
that none of the engineers saw this as an opportunity to develop a mechanical
stoker that could work well with lump coal, like Scheffel did for improved bogie
design.
To cut a long story short, the tests gave a clear indication that the following
changes should be worked into the new class 25 boiler design, as shown in Fig 18a
& 18 b, to increase the efficiency by at least 5 percentage points over the medium
to high firing rate range:
• Increase the number of air holes in the fire grates as far as practical, but not
their size.
• Reduce the downward slope of the firebox grate to about half that of the 3B
boiler.
• Increase the angle between arch and grate from 25o on the 3B, to 30o
• The brick arch top centre to be in line with the centre of the grate, and a bit
shorter at the sides
• Preferably use siphon tubes to support the brick arch rather than arch tubes
• Reduce the breadth of the grate
• Make the grate area as large as the weight limitations will allow
The Standard Stoker design was retained in spite of it leading to low boiler
efficiencies.
A ‘combustion chamber’ was introduced at the firebox front end. It is needed to
reduce maintenance costs: it would not influence the efficiency.
These changes were incorporated into the Cls 25 boiler, which proved to be very
successful. The grate size became 7’ x 10’ (3B was 8’ x 8’), giving a 12% greater
area; siphon tubes were used and a combustion chamber fitted, which meant that
the boiler tube length could be reduced from 22’ 6” to 19’. For a given steam
production (Power output), the coal consumption was reduced by about 20% at
fairly high power levels on the cls 25. It could, however, only be achieved by
replacing the two-wheel trailing bogie under the ash pan with a four-wheel bogie.
5.3 Boiler Efficiency - Cls 26
In Appendix B1 a general summary is given of the changes effected under
Wardale’s supervision on a class 25NC locomotive to improve its efficiency and
power. It became the (only) Cls 26 locomotive. The changes are shown somewhat
diagrammatically in Fig 19, in order that they can be compared easily with the
normal boiler shown in Fig 14.
The most important change is the diverting of some exhaust steam from the
cylinders to the ash pan, from where it is sprayed under the grate to mix with the
air as it reaches the burning coal. The steam reacts with the hot coal to form
hydrogen (H2) and carbon monoxide (CO) gases. The reaction partially cools down
20
the coal to a dull red heat. A portion of the carbon still burns to CO2 which keeps
the coal sufficiently hot. Presumably some care is needed to regulate the ratio of
steam to air, so that the best working conditions are maintained. The flow rate of
the steam-air mix is much lower through the grate than that of the air in the Cls 25
boiler, so that the loss of coal particles is greatly reduced. Extra air is now
introduced from the sides, presumably just above the grate, to allow the H2 & CO
mix to burn as completely as possible. The process certainly lends itself to better
boiler efficiency, but probably not much better than with hand-firing, if one takes
into account that the steam which is injected before the grate, leaves the boiler still
as steam, but its temperature is now probably around 250o C compared to about
100o C on the Cls 25 locomotive as exhaust steam up the chimney - a loss which
will counteract some of the gain.
It would have been really interesting to have given the Porta/Wardale principle a
go at the Laingsburg tests in spite of our time limits, had it already then been
effectively used elsewhere. It was not yet so; we can only think of the Cls 26 as
being a real Red Devil who had come with too much, 30 years too late.
5.4 Boiler Maintenance
The design of a boiler from the strength and low maintenance point of view was
largely based on experience gained from older designs. Some of the factors which
influence the design are the enormous loads due to the high boiler pressures (up to
225 lb/sq in), differential expansions due to varying temperatures as the steaming
rate changes and particularly when the boiler is shut down and restarted for boiler
shut downs, and the fact that the boiler takes some of the frame load.
Some idea of the pressure effect can be obtained by noting that on the Cls 25 the
boiler cylindrical barrel has to resist an outward force of about 300 tons per foot
length. The load forcing the firebox crown plate down, away from the boiler shell
is about 1000 tons. This explains why there is a veritable forest of stays between the
crown plate and the outer boiler roof as can be seen in the sectional drawing of a
class 25 in Fig 20. The stay support continues on all sides of the firebox: here the
stays are short (about 6” between plates) and they are stressed further by lateral
movement between the plates. The firebox shell heats up quicker and reaches a far
higher temperature than the outside plate: the differential expansion which leads
to bending of the stays was so high that it led to failure of the stays and the plates
to which they are fixed within two years on some 3B boilers. They were replaced
by flexible stays. Between the stay head on the outside of the boiler and the shell is
a washer with ridges, as shown in Fig 21. I do not have its formal name, but let us
call it a rocking washer. It allows the stay to cant a few degrees in any direction,
sufficient to eliminate the worst bending stresses. Simple, but it works well even
under the dirty water conditions in the boiler. More judicious use of these and
other types of flexible stays in the Cls 25 led to vastly reduced maintenance costs.
A further improvement was to get rid of the curved Wooten firebox: under the
steam pressure it tends to straighten, leading to additional stresses in the firebox
21
inside plates and in the boiler shell. These improvements far outweigh the small
loss in combustion volume above the arch.
Further strength improvements were made by more use of welded joints - the
quality of welds had reached the stage that the welded joint was stronger and
more reliable than the overlap riveted joint. It is also lighter. The best example is
the replacing of the solid and very rigid foundation ring (it is really a rectangle!) of
the firebox with a U-shaped ring made from steel plate of similar thickness and
welded to the boiler and firebox plates (Figs 18b & 20). It keeps to the same
temperatures as the plates and has the same stiffness. Weight is saved, even
though a cross stay was fitted between the two sides of the firebox. I can vouch for
it that rapid changes in the cross-sectional areas of stressed members are highly
detrimental to the long-term strength of the member - it becomes prone to fatigue
failure. These changes were all steps in the right direction.
Moving on to the boiler as such, a combustion chamber was fitted, mainly to
reduce the length of the boiler tubes, as was mentioned in Section 5.2. The length
was reduced from 22’ 6” to 19’. It led to some tenfold increase in the life of the
tubes without any difference in the boiler efficiency, as proven on a Cls 23 test.
The main differences between the 3B and Cls 25 boilers around the firebox are
shown diagrammatically in Fig 18.
Regarding Tubes, the old practice of placing as many as practical small (2½”
diameter) tubes in the lower two-thirds of the boiler barrel and the 5½”
superheater tubes just above them has proven effective and was retained for the
Cls 25. The number of tubes in the Cls 25 was increased as the boiler diameter
could be increased slightly over that of the 3B (see the notes in the diagrams of
Figs 7 & 10 for details).
5.5 Smokebox
The combination of the Blast Cap with the Blower around it in the bottom of the
smokebox and the Petticoat plus Chimney aligned above them is the key to the good
functioning of the locomotive (Fig 22). On 3211 the angle of divergence of the
exhaust steam jet was 17o as measured from the top of the blast cap to the neck
(smallest diameter) of the petticoat/chimney, and 7¼o in the chimney from the neck
upwards. This should be taken as a good guideline, but the best angle does vary a
bit with size and the distance the jet travels. I must leave it to the likes of “MM” or
THE Test Engineer during my time, Nick Bestbier, to do the full calculations for
the new big loco you want designed! I do know that if the angle is correctly
chosen and the loco lags a bit on steam output, the best cure is to fit four ‘tips’ onto
the top of the cap (Fig22) to give the steam jet a bigger surface area to drag in the
smoke without disturbing the jet angle and to slightly increase the ‘back pressure’
of the steam - increased jet energy and speed. Loco 3211 had four tips of 5/8” x 1-
22
3/8” which reduced the cap area by 8%. How do I know? Check Fig 23 taken at
Laingsburg.
My dad told me about his experiences with blast caps and chimneys, way back
around 1926. He was called out to check one of the early Garratt engines that were
poor steamers. The locals had fitted a smaller blast cap to get a stronger blast, but
to no avail. “MM” borrowed a fishing rod (was it in Natal near the coast?), tied a
bit of old rag around the tip, and let the driver start her at full power. As he put
the rod’s tip next to the chimney top, the rag was torn off - and sucked into the
smokebox! The cap was so small that the exhaust jet never touched the side of the
chimney. Fitting a bigger cap with tips solved the problem and raised “MM”s
reputation a lot.
One is inclined to relate a sharp bark from a loco as a symptom of a good steamer.
Not always. The 15CA we tested at Laingsburg had the same size cylinder and
wheels as the 15F but the grate size was only 48 sq ft. Consequently a much
smaller chimney and cap was fitted to overcome the increased flow resistance
through the grate and boiler. You could hear the bark from miles away, and she
kept her boiler pressure, but the maximum power output was far smaller than that
of the 15F or 23.
Char Steam locomotives can be nasty neighbours to forests and dry fields due to
the burning coal particles or char blown out, leading to fires. In an attempt to
reduce this risk, the so called American Front End is fitted to all smoke boxes (Fig
22). The back Diaphragm Plate and the lower Table and Breaker Plates help to break
up the larger burning particles, and the deflector also directs a strong smoke flow
to the bottom front of the smokebox where char otherwise tends to accumulate.
Lastly, the smoke plus remaining char has to pass through the front spark arrestor
plate which is perforated with holes of about 1/8” x 3/8”. Their total area is about
20% more than the area of the boiler tubes so that the extra resistance to flow is
relatively small.
The main problem that does sometime happen is that the plates deform when
overheated, particularly if the smokebox door does not seal perfectly and air leaks
in setting fire to unburnt gasses and char. Big gaps open in the spark arrestor and
large burning particles escape up the chimney. The extra heat warps the smokebox
door even more, so the problem keeps getting worse. (I was going to say that it
snowballs, but somehow that does not sound suitable!)
5.6 Safety and Other Ancillaries
5.6.1 Boiler Steam Pressure Gauge
The gauge is mounted in front of the driver and fireman (Fig 24), with a red line
drawn on the dial at the prescribed maximum boiler pressure. The gauge is
regularly checked and adjusted by the maintenance staff and then sealed.
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5.6.2 Safety Valves
At least two safety valves are fitted onto each boiler. A large boiler with little
space left on the top such as the GMAM, has four. They are set and sealed by the
maintenance staff; one blows at the set boiler pressure and the next at one or two
lb/sq in higher. This makes it clear to the footplate staff that when the second
safety valve also opens, they are steaming well above the mark, encouraging them
to take other steps such as to cut in the second water injector.
Older locomotives were fitted with Ramsbottom valves (Fig 25a), but they were
succeeded by Ross-pop valves (Fig 25b) which became the standard. They were
already in use on the first cls19 in 1928. Ramsbottom valves have the disadvantage
that they are slow to open and only close when the boiler pressure drops to about
5lb/sq in below the opening pressure. This may stall the locomotive when starting
a heavy train, and leads to a considerable loss in energy.
The Ross-pop valve does not have these problems. It makes use of the principle
that when the valve starts to open, when the pressure on that part of the valve
which is exposed to the boiler just exceeds the valve spring load, it immediately
exposes a further area on edge of the valve to the full steam pressure, and the
valve opens rapidly with a ‘pop’ sound, hence the name. The steam then jets out
through the many holes in the valve head reaching the top of the valve where it
blasts out through the six or so holes in the top cover. It lifts the cover with the
spindle, as well as the actual valve at the bottom, allowing a large flow of steam to
occur rapidly. The rate can be adjusted by the maintenance staff (and sealed!) by
closing one or more of the top holes. When the boiler pressure drops to a fraction
below the set boiler pressure, the reverse takes place and the valve closes with
another ‘pop’.
The Ross Pop valve has proven itself and remains the standard safety valve in
spite of its higher manufacturing cost.
5.6.3 Water Gauge Column
It is critically important that the footplate staff should at all times know where
the water level is in the boiler. The water level has to be ‘managed’. There must
always be at least a few inches of water above all parts of the firebox crown to
prevent overheating of the crown plate and melting of the fusible plugs (See
Section 5.6.4). However, it does not help to increase the water level to say a foot
above the plate, for then the boiler is almost full and the surface area of the boiling
water has reduced so far (due to the cylindrical top of the boiler) that the steam
tends to prime, ie the intense flow of the steam drags water with it. The superheat
temperature drops rapidly. Some of the water may be carried through to the
cylinders. In the worst case this can lead to the rapidly moving piston (up to 5
strokes per second) to bang out the cylinder covers or fracture the cylinder casting.
24
Water, unlike steam, is incompressible and at the end of the piston’s stroke the
steam port is closed.
A complication which the driver has to keep in mind is that the level of the water
shown in the water gauge relative to the water coverage over the crown plate
depends on the locomotive’s position and how the steaming rate changes. For a
Cls 23 locomotive going up a 1/60 gradient the gauge will show about 3” higher
and after going over the top and drifting down the 1/60 downhill, 3” lower than on
the level - a change of about 6” for the same amount of water in the boiler!
Standing on a curve which is canted (Fig44), will show about 6” difference
between the two gauges. Another factor is that when the boiler is steaming hard
the large number of steam bubbles in the water makes the water level rise and vice
versa; lastly, braking hard leads to a drop in water level at the back of the boiler, ie
over the crown. It needs a lot of experience to make all the right decisions!
Coming back to the water gauge, from the above it becomes clear why there is no
red line to show what the correct level is and why there are two columns: one near
the driver, and one near the fireman, as both help to keep the water at the right
level for the given condition.
The column is essentially a pyrex glass tube fitted in a vertical position. It is about
a foot long, connected top and bottom via cut-off cocks to the inside of the boiler
(Fig 26). Under normal stationary and level conditions with both cocks open, the
correct water height would be near halfway up the tube.
In view of the high temperature and pressure conditions, many safety features are
included. Even pyrex glass is slowly but surely dissolved by boiler water, it may
fracture unexpectedly at any time before the normal replacement period. A thick
three-sided armour-plated glass shield is fitted around the column which shields
the footplate staff from flying glass shreds as well as the water/steam outburst. The
reducing and ball valves in the cocks should stop the flow, but sometimes they do
not work well. I have not personally experienced such a failure, but I accept that
sometimes all Hell is let loose, as everything is obscured by the steam cloud. The
footplate staff dive out of the cab hanging onto the outside, until one of them can
wrap a thick wad of cotton waste around a hand and reach in to close both cocks.
Thereafter they can slowly recover their wits and replace the column tube - the
driver always has a spare on hand - but first they must regain control of the
locomotive!
5.6.4 Fusible Plugs
The Fusible Plugs (Fig 27) are screwed into the crown plate from the bottom. On the
larger locomotives there are three: one at the centre back, the other two in the
front, one on each side. This protects the crown plate under low water conditions,
also under high or low gradient as well as cant conditions. The plug is filled with
lead which projects into the boiler water. As the melting point of lead is 327ºC and
25
the boiling water temperature is about 200ºC, the lead will not melt, but if the
water level drops below the top of the plug (ie with about ½” water still covering
the plate), the steam cannot cool the lead sufficiently and it will melt: the steam jet
will blast down into the firebox, enough to quench the fire in a standing
locomotive but not on a running engine. However it will alert the footplate staff
who knows they must get both injectors going and start quenching the fire. Failed
in section again! But rather that than a boiler explosion when the crown plate
overheats and implodes.
It must have taken someone quite a time - probably by trial and error - to get the
proportions of the plug just right so that it does the job when it must, without too
many premature failures. Another simple but effective device. They are renewed
at every boiler washout.
Have there ever been any boiler explosions on the SAR? I have heard of only one
case which happened on a locomotive in the Free State heading south for
Bloemfontein with a goods train. It was late on a dark, stormy night in the pelting
rain when they took water at Glen from the Modder River, scrambling back into
the cab as soon as possible. At Bloemfontein they were unexpectedly diverted
onto a sideline in a deserted yard and received a warning to put on the injectors
then get out and run as far and as quickly as possible. Looking up into the firebox
they saw that the crown plate was red hot and bulging already - they got out just
in time. Apparently the storm had muddied the water that had been used to fill
their tender at Modder River (!) to such an extent that a layer of mud settled onto
the crown plate and became baked in position. It also choked the fusible plugs .The
steam did not penetrate the clay layer sufficiently to warn them. One of those one
in a million accidents. (The train after them at the water station had sufficient
light to notice the problem and the loco plus station staff did some quick thinking
to get the warning through).
5.6.5 Injectors
Injectors are there to pump the cold feed water from the tender into the boiler
under operating conditions - maybe not primarily a safety device but more part of
the operating components; however, if they don’t work ----.
In Europe the feed water is pumped into the boiler with a piston pump, driven by
a steam engine, but we have standardised on the injector which has only one
moving part and already preheats the water to quite an extent, all in one
operation.
In Figure 3 of a class S1, the stoker is leaning out of the window looking at the
injector from which some steam is blowing to the rear. Fig 28 is a cross-sectional
view of an injector. The components are all made of bronze. Injectors are
mounted vertically downwards under the footplate, as shown in the figure, in the
lowest position practical - the water from the tender must be able to flow down
26
under gravity Steam from the boiler and the water from the tender are fed to the
top of the injector. The stoker can regulate the flow rate of each individually by
controls in the cab which operate valves on the inlets. The steam flows from the
inlet at the top through the steam cone which first converges, then diverges. This
shape causes the steam to become a very high speed jet at a low pressure, so that it
will suck the water into the annular opening and into the mixing cone, where the
steam condenses with the feed water to form a hot water jet. The partial vacuum
in volume A now sucks up the movable suction cone until it seals at the top,
cutting off contact with the overflow pipe at left. The flow of water out of the
injector stops and the fireman now knows that he has set his control valves
correctly (that is what is happening in Fig 3).
But how does the water manage to overcome the boiler pressure? When the hot
water jet leaves the mixing cone at B it is travelling at a very high speed. As it
flows down the diverging delivery cone, the drop in speed (by a factor of about 6)
leads to an increase in pressure by a factor of about 6x6, which is sufficient to
force the water up the delivery pipe to the top of the boiler, open the non-return
valve and overcome the boiler pressure.
There are helical vanes around the movable cone, but they are not there to spin the
cone: their sole purpose is to keep the cone accurately aligned with the mixing
cone. Straight vanes would lead to groove wear of the injector body and decrease
its life. They have a lot of work to do; a Cls 25 can consume about 5000 gallons of
water per hour.
5.7 Keeping the Boiler Clean Inside
We all know how the tea kettle keeps liming up and forming a dirty white sludge
over the months - particularly with Karoo or dolomitic waters. The loco boiler has
the same problem, but it is roughly 100 000 times worse. The SAR had a Section
working on cleaning up the water before it was made available for the tenders, but
it proved impractical to do it to the ideal limit. They tended rather to concentrate
on making additives available to reduce the tendency for the boiler to prime (See
Sect 5.6.3, first paragraph). So the footplate and shed maintenance staff had to
take care of the problem - it would literally be fatal to have lime build-up on the
crown plate. The following facilities were made use of.
5.7.1 Blowdown Valve
At the lowest point on each side of the boiler a large valve is fitted which can
release water from the boiler. These can be operated from the cab. To be effective,
a strong jet must be released to carry with it the sludge and the saltiest water that
accumulates there. The outlet is formed to blast out sideways. The driver must
ensure that it is only used where it will not cause problems. It is quite a sight, as
seen in Fig 29. It is used a few times per day. Obviously the injector(s) will also be
on while the blowdown is in operation.
27
5.7.2 Washout of the Boiler
In addition to the above, boilers need a thorough washout at regular intervals,
every one to three weeks depending on the conditions. This is one of the big
factors leading to low availability of the steam locomotive. The fire has to be
dropped, the grate cleaned and the boiler cooled down before it is safe to open the
many plugs screwed into the boiler at strategic places and drain the water. The
boiler can then be inspected internally through these openings before the washout
crew bring their high pressure hosepipes to flush out the remaining muck. Minor
repairs can also be carried out, eg to leaking valves. Then the fusible and washout
plugs are replaced before the boiler is refilled and started up as was described in
Sect 4.1. A day or more is lost with every washout.
The question which has to be answered is could these problems be overcome by
feed water treatment? It could only be possible with distilled water, as is done at
the large power stations, but there the steam is condensed as part of the power
cycle and the quantity of make-up water is minimal. The nearest we came to it is
in the condenser locomotive Cls 25, where the exhaust steam was condensed to be
re-used, but the make-up water was still Karoo water. Washouts could be
reduced, but other maintenance problems outweighed this advantage and the
condensers were all converted back to the non-condenser Cls 25NC in later years.
They were then no longer operating in the drier Karoo areas.
6 The Engine of the Locomotive
Summary: Why reciprocating instead of rotating turbine engines? - Cylinders and
pistons - Rods - Driving wheels - Control of the steam - Regulator and Walschaerts
valve gear - Bearings and axle boxes - Frame - Coupling to tender.
6.1 Reciprocating vs. Turbine Engines
Question: “Why were turbines not used as the driving engines on our
locomotives? After all, ESCOM uses them on all their power stations, manages to
keep practically smoke-free fires going and produces electricity with something
like 30% efficiency, in spite of the poor quality coal they use. You can get rid of
the complex set of rods and slides to turn the wheels! After all, it was used in the
50’s or so in the USA” Yes, on a few engines for the hard run over the Rockies -
but not for long before they disappeared.
The answer lies in several drawbacks that become dominant if the ESCOM system
is forced into a relatively small space on a loco which has to perform over the
whole range from fast reverse to very fast forward. Firstly, the turbine has a very
good performance at one fixed speed only: its power output and efficiency drops
rapidly if the speed exceeds or falls below the design speed; moreover, it usually
has a ‘critical’ speed a bit below the design speed at which a strong resonant
vibration occurs - it must be accelerated through that speed to prevent damage. It
is a no-no part of the speed range. As far as its high efficiency is concerned, much
of it is due to a system where the exhaust steam from the high pressure turbine, is
28
allowed to expand through a very large turbine, which is many times as large as
the high pressure turbine. The size of these two combined will be larger than the
locomotive engine. The steam must also expand to a pressure well below
atmospheric into a LARGE condenser sealed from the atmosphere. The condenser
again has to be kept as cold as possible (below 20º C) by cooling water from the
cooling towers. Remember the concrete )(-shaped towers, maybe 300’ high, at
Arnot and other Power Stations? That’s them! Cooling down by a fan system as on
the Cls25 condenser tender, is enough to regain the water from the exhaust steam,
but you need far more than that to get the sub-atmospheric pressure essential for a
high efficiency. Lastly, as far as the mechanics are concerned, the turbine needs to
run at a high speed which means building in a large gearbox, with the possibility
of changing gears as in a car (Say three-speed) AND with a reverse gear, as the
turbine works very poorly in reverse. No go! In contrast, the reciprocating
engine with a Walschaerts valve gear can develop full power (within the limits of
the boiler capacity) over the whole range of speeds from backwards to forwards.
What is more, the changes can be made effortlessly and smoothly without steps,
with one control lever.
The last alternative would be to go for a turbine - electric generator system,
exhausting to atmosphere, with electric motors on the driving wheels: rather like
the Diesel-Electric locomotives. It would probably lead to a locomotive mass of
about 1½ times that of the already overweight standard reciprocating locomotive
(Check Tables B1 and B2 in App B), which is enough to discourage any engineer.
It was never tried as far as I know.
I am not surprised that the turbine locomotive did not make the grade and that
that Old Man Piston was retained for two centuries.
6.2 Pistons and Cylinders (Fig 30)
The Piston (A), bolted to the Piston Rod (B), reciprocates (ie moves backwards and
forwards) in the Cylinder(C). Our surviving locomotives were all built with one
pair of outside cylinders per engine. The few that were tried with an additional
cylinder or two between the frames were found to be impractical and soon
disappeared (See Section 3 and Fig 13).
The cylinders are double acting, ie the piston is power driven at both the front and
the back strokes, in contrast to your car’s pistons which are only powered on the
down stroke, and that only at every second rotation of the crank.
With one pair of cylinders the locomotive can therefore be started from any
position provided that the Driving Wheel Cranks are positioned at a quarter turn
(90º) to each other - see also Section 6.4 and Fig 34.
The basic double acting steam cycle is briefly as follows: Let us start with the
piston in its full front position (In Fig 30 it is shown in the midstroke position ; the
29
front position is shown in the diagrammatic sketch Fig 31a, with its corresponding
Connecting Rod (Also Fig 30D) and Crank Pin (Fig 30 I)positions). The Front Port is
admitting live steam into the front part of the cylinder which pushes the piston
towards the back past the middle position (Fig 31b) with a force as high as 50 tons
compression on the piston rod until it reaches the end position (Fig 31c). During
this period the volume behind the piston, ie to its right, has had the steam port
open to the exhaust and its pressure against the piston has been a small fraction of
that on the front side. The Connecting Rod has also in the meantime forced the
Crank Pin and the Driving Wheel round half a turn. The cycle now reverses: The
front steam port is now open to the exhaust and the back port to the live steam.
The Piston Rod Gland (Fig 30E) now plays its part to prevent the live steam from
blowing past the piston rod into the atmosphere. The piston is forced to the front
ie to the left, the piston rod and the connecting rod are in tension to nearly the
same force as in the first part. (There is a small loss in load due to the reduction in
surface area of the piston by the piston rod). The wheel keeps rotating anti-
clockwise (Fig 31d). When the piston reaches the end of the back stroke the cycle
is complete and the sequence starts again as in Fig 31a - except that the engine is
now one wheel rotation further down the line.
Further refinements in the cycle such as live steam Cut-off before the stroke is
complete to allow expansion of the steam (already shown in Fig 31) and Pre-
compression will be dealt with later when the valve gear is described on p24.
The piston is usually made of steel with an almost bell shaped disc, the purpose
being to reduce the thermal stresses when it is suddenly exposed to superheated
steam. The outer sleeve is of cast iron for less wear on the cylinder liner. In
addition its bottom is extended to form a slipper to reduce wear still more. In
Europe, a more elegant solution was to extend the piston rod through the front
cover where it could be supported - but another gland had to be fitted to prevent
steam leakage.
Cast iron piston rings are fitted into grooves around the piston’s outside to limit
the leakage of steam from one side to the other. They wore rapidly and were part
of the replacement program when the locomotive came for its 15M running repair
ie every 15 000 miles. An improved design was used for the cls 25, which lasted
much longer, but I do not have the details.
6.3 Rods
We have already had an introductory glance at the most important rod, the
Connecting Rod. We remain indebted to Trevithick and Stephenson who broke
away from the cumbersome planetary gear system as used by Watt of converting
reciprocating motion to rotation, by making the connecting rod do the work.
The connecting rod is coupled to the piston rod via the Crosshead (Fig 30F): the
back end of the piston rod is tapered, fitting neatly into the crosshead front end
30
where it is locked in position by a flat tapered locking pin. To remove the piston
for maintenance, the front cylinder cover is removed and the crosshead locking pin
extracted, where after the piston with its rod can be pulled forward through the
gland opening and out. Just behind the piston rod joint is the round Gudgeon pin
(Fig 30H), inserted from the inside through the Small End of the connecting rod
and locked on the outside. A smaller diameter part of the pin projects a few inches
further to carry the Union Link (Fig 30G), which will be dealt with in the next
section.
The crosshead’s function is to keep the piston rod dead in line with the centre of
the piston plus cylinder. It has to resist the high vertical force acting on it of 15% of
the force on the piston rod, ie up to 7 tons at midstroke. This vertical force is
caused by the angle of the connecting rod’s force relative to the piston centreline.
At the same time the crosshead is rubbing backwards and forwards against the Top
Slide Bar (Fig 30S) at a speed of up to 25 mph. (With the engine in reverse, it will be
forced downwards onto the lower slidebar). So the crosshead is made of steel,
with the steel shoe between the slide bars given a thin layer of white-metal both
top and bottom for a better bearing surface. It is well lubricated but with all the
dust swirling around, it often overheats, as we experienced at Laingsburg - see
Figs 32 and 33 - and the white metal melts. The loco has to drop its load, and then
run slowly to the nearest loco depot, with plenty of cylinder oil on the slidebar.
Whence the name Crosshead? On our older locomotives, eg the Mallet in Fig 12, the
whole crosshead fitted between a top slide bar above the centreline and a bottom
slide bar below the centreline. Viewed from the side the crosshead then had an X-
shape, hence the name. This design was repeated for the Cls 25. The symmetric
shape of this type of crosshead eliminates inertia bending stresses on the piston
rod which are found during high speeds with the Fig 30 design. It is still shown in
the drawings of Fig 10, but the engines were converted back to the 1930/50 design
after only a short period of service, as can be seen in the photographs in Fig 10 and
11. I don’t know why.4
As mentioned before, the Connecting Rod transfers the piston force to the driving
wheels of the engine. Its Big End fits around the Crank Pin (Fig 30 I) which is force-
fitted into the Driving Wheel (Fig 30J). Connecting rods are big brutes - they have
to be, taking into consideration the high forces they have to transmit (Up to 35 tons
on the Cls 19 and 50 tons on the Cls 25, oscillating between tension and
compression during each stroke, up to 5 times per second). More about these
stresses are dealt with in section 7.1.
In Fig 34 the positions of the crank pins in a driving wheel can be seen. The crank
pin on the right hand wheel is always leading when running forward, on all SAR
engines. The bearing between the big end and the crank pin is subject to high but
varying loads and high rubbing speeds, which makes for difficult bearing
conditions. The normal design was to fit a floating bush (Fig 35a) between rod and
4 See Les Pivnic’s comment - HBH
31
pin. The series of chamfered holes in the bronze bush were filled with hard
grease, regularly augmented by the driver. The grease came in sticks about ¾”
diameter, forced into the bearing with a cantilever grease gun (Fig 36). In spite of
these efforts, overheating of the big end bearing happened too often, as seen in Fig
36. The problem was only solved on the Cls 25 by fitting Timken Double Taper
Roller Bearings (Fig 35B) instead of the floating bush.
The repetitive high stresses on the connecting rod under hard running conditions,
occasionally led to their failure, usually close to the small end. One can imagine
how the rod front point would fall down and jam into the track sleepers, with the
possibility of throwing the locomotive onto its side. To prevent this, a form of
Safety Strap was often fitted to engines (See eg Figs 1 & 6) to catch the broken rod
before it stuck into the track.
6.4 Coupled Wheels
In Stephenson’s time, the engine could pull its load with only one driving wheel
set, but it soon became clear that more would be needed as loads increased. It
became common practice to fit more wheel pairs of the same size Coupled to the
driving wheel. Figures 1 & 6 show three Coupling Rods connecting the driving
wheel to the other Coupled Wheels on a so-called Eight Coupled engine. They share
the traction force equally with the driving wheel - they all pull together, or slip
together. The front and the back coupling rods are connected to the intermediate
coupling rod with Knuckle Pin Joints to allow slight relative vertical movement
within the limits of the spring suspension system dealt with in Section 7.
There are limits to the number of wheel pairs that can be used. If 5’-0”d (1524mm)
wheels are used, four coupled wheel pairs are the maximum which can
comfortably negotiate the sharpest SAR curve of 300’radius. At 5’-3” d, the class
23 could just squeeze round the curve, but the additional lateral loads on the frame
contributed to its early failure. If a ten-coupled wheel arrangement is used, the
wheel diameter would need to be around 3’-8”d, which means it, would not run
well at speeds over about 40mph - too low for main line working. The
experimental Cls 18 locomotive (ten-coupled) used 4’-9’’d wheels, of which two
pairs were flangeless: she derailed regularly, was rarely used, and was soon
scrapped. In any case, if a ten-coupled main line engine is to be used to the full, it
would need to have bigger or more than one pair of 24”d cylinders. There is really
not enough room on the outside of the frame for bigger cylinders, so that a third
cylinder would have to be fitted between the frames, as was tried on the class 18 -
without success. The only alternative that was tried and worked well within limits
was the GMAM Garratt which with its auxiliary water tank kept the load on the
driving wheels a bit nearer constant. Its tractive effort is 134% of that of the Cls
25NC, but its limitations lay in the 4’-6” driving wheels which made it too slow for
Karoo main line working. An engine should not work at speeds greater than a mile
per hour for every inch of the wheel diameter ie 54 mph for the GMAM .
32
As mentioned above, the Crank Pin Spacing of 90º. (It needs a special boring
machine with a hefty support for the heavy wheel to do the machining known as
quartering, in the workshops) does enable the locomotive to start from any
position. That, plus the connecting rod angularity (a maximum at midstroke), does
however lead to several problems, ie
• The tractive force on the track is not constant. At slow speeds it varies by about
30% between maximum and minimum at constant steam feed pressure in the
cylinders. It calls for some expert juggling of the regulator by the driver on
starting to reduce the effect to a minimum. The effect reduces as the speed
increases.
• The weight of the crankpin plus the connecting rod big end plus the coupling
rods and their pins, is out of centre on the wheel. It has to be balanced by a
counterweight on the corresponding wheel and another small counterweight on
the other wheel of the wheel pair, because the counterbalance weight has to be
fitted on a slightly different plane than the connecting rod. (The mechanics of
this exercise becomes quite complicated and will not be dealt with in detail.
Engineers can read all about it in Ref 5, Appendix 2. I will be happy to supply
copies on request). The out of balance weight is about 1000 lb per side for the
Cls 23 locomotive. With correct counterbalancing this potentially disturbing
effect is eliminated at all speeds.
• The backwards and forwards reciprocation of the pistons, piston rods,
crossheads and the front part of the connecting rods causes an oscillation of the
engine. The mass is about 1300 lb per side on the Cls 23, stroking at 28”. The
sum effect of both sides is about 1800 lb at 28” stroke for the two combined. If
left unbalanced, it would lead to a backwards and forwards oscillation of the
115 ton (230 000lb) locomotive (less tender) of 28” x 1800 ÷ 230 000 = approx 0,
2” stroke, which is not acceptable. It is not practical to fit a horizontally
stroking counterbalance to eliminate this oscillation, the best that can be done
on a two-cylinder engine is to fit a further counterbalance weight opposite the
crankpin which will reduce this oscillation, but it leads to a vertically oscillating
force, called the hammerblow, onto the track. It is not really felt on the
locomotive, but the additional force on the track can cause problems to civil
engineering structures. The civil engineers limit this additional load to 1½ tons
per axle at 45 mph, which means that the oscillation can be reduced only by a
quarter, ie to 0,15” stroke.
• There is one further step that can be taken and which proved practical, that is
to couple the tender and engine so tightly that as far as the backwards-forwards
oscillation is concerned, they act as one body. The details will be dealt with
later, but with this coupling of the Cls 23 to its 107 ton tender, the oscillation
reduced by one half to about 0,08”, with which we can live. (Where an engine is
fitted with three or four cylinders, the abovementioned horizontal oscillation
can be greatly reduced and the hammerblow is small.)
• The next problem is caused by the sum of the two connecting rod forces being
alternatively on the right and the left side of the engine. One has to keep in
mind that the high pressure steam in the cylinder not only tries to push the
piston, it is also pushing the corresponding cylinder cover with the same force
33
in the opposite direction. This tends to slew the front of the engine once to the
left and once to the right per every one revolution of the driving wheels. On the
cab of the locomotive one can feel and even see this movement if you look
forward along the track. It is most noticeable at slow speeds when the
locomotive is pulling hard, and it gradually reduces as the speed increases and
the tractive force becomes smaller. (To the applied mechanics experts: yes, I
know this is a bit of a simplification, but I can vouch that the slewing did take
place on the Cls 23 - not normally on the Garratt.)
• Lastly, there is the unbalanced vertical force of the crosshead onto the slidebars,
a maximum at midstroke, reducing to nil at the ends of the stroke when the
connecting rod is in line with the piston rod. When running forward, the force
is upward both on the forward and on the backward stroke. Due to the quarter
circle difference in the positions of the left and right crankpins, we now find a
force of up to 7 tons trying to lift the front of the engine alternatively on the
right and the left side near the front, not twice but four times per revolution of
the driving wheels. As the force is only a fraction of the previously mentioned
slewing force, the effect is much less but still noticeable at slow speeds. What
one feels is a small tendency for the locomotive to cant (to roll from side to
side), at twice the rate of the slewing action. I was not aware of any tendency for
the locomotive to sway up and down, the loco wheel base length of 37’ is too
long for those forces to have much effect, whereas transversely the alternate
vertical forces are at twice the span of the restraining wheel support on the
rails.
Well, let us try to simplify matters by saying that a locomotive like the Cls 23 has a
most interesting, I would even like to say fascinating or creative quality to its
movement, particularly when it is starting to pick up speed - it is not just a smooth
pulling away which one finds with an electric locomotive. In a sense it has
something challenging to it, like the movement when riding a horse up an incline
in comparison to driving up in a modern smooth running car.
To be more mundane, the motion of the locomotive pulling at slow speeds has
something in common with a goose waddle as viewed from behind, but not so
extreme. The goose has the sideways slewing waddle and the forward and
backward oscillation, but to this must still be added the double frequency roll
which is unique to the steam locomotive.
6.5 The Control of the Steam
The locomotive, like the motorcar, has two regulating mechanisms to control the
power output at a given speed. The motorcar’s accelerator (petrol pedal) controls
the energy feed rate, ie the petrol; the corresponding function on the locomotive
being done by the Regulator which controls the steam flow rate to the cylinders
and, moreover, can stop it altogether. In addition, the locomotive also needs a
control of the feed rate of the primary energy source, ie the coal, by the fireman
directly by his shovelling rate, or by adjusting the mechanical stoker speed.
34
The function of the car’s gearbox is taken over on the locomotive engine by its
Valve Gear. It is far more flexible than the gearbox, as it has a steplessly variable
control from ‘hard forward’ through neutral to ‘hard reverse’, regardless of the
speed at which the engine is running.
In both cases operating the brakes is a separate function which will be dealt with
later.
6.5.1 Regulator
The Regulator Valve on older locomotives is a large valve in the dome of the boiler.
In the locomotives being considered, several small valves working in parallel are
fitted into the header in the top of the smokebox (Fig 14). In both cases, control is
by a lever at the driver’s left hand, coupled by a long rod to the valve.
The valve shown in Fig 37 is the type used on the older locomotives, but the
principle is the same on the modern locomotives with up to 8 smaller valves which
open one after the other as the regulator lever is pulled open. The control is better
and requires less brute force by the driver. The valves are of the Double Beat type,
ie there is the same full boiler pressure on both ends of the valve when closed,
making it possible for the driver to open the valve gently without extra power
assistance. Quite simple but effective. It does mean that both valve faces have to
be carefully lapped in so that both seal simultaneously, but that seems not to be a
problem.
It has been found expedient to regulate the saturated steam before it passes to the
superheater elements. It is safer if leaks develop in the elements as the regulator
can shut them off and the valve life is also increased. The time delay for the first
steam to reach the cylinders is negligible. Steam locomotives don’t run in 100m
sprint competitions.
6.5.2 Valve Gear
The function of the Valve Gear (Fig 30) which controls the Piston Valve (Fig 30 I),
which in turn opens and closes the Steam Ports (Fig 30J) to and from the cylinders,
is difficult to describe on paper; it is best dealt with by demonstrating the
movements on a scale model. To this end, a model of the Walschaerts Valve Gear
was built by the author (See Fig 38). The scale is approximately 1: 10, which is
adequate to show the piston valve function and how it is influenced by the Cut-Off
settings. What follows is more of an explanation of what is needed than the details
of how it is achieved.
To expand on the summary given in Sect 6.2, p 19 - 20, on the action of the steam in
the cylinder, the valve gear has to perform the following functions (For
convenience, we will look only at the front part of the cylinder - Fig 39a - with the
engine starting off with the piston in front dead centre (FDC) in forward ‘gear’;
35
rotation therefore anti-clock). The figure is not to scale so that the port opening can
be clearly shown:
1. (Stroke 0%. Rotation 0º); the port is already fully open to steam inlet; it started
to open up just before FDC. Port fully closed to exhaust.
2. The best use of the steam is to ‘cut-off’ the inlet along the stroke, somewhere
between 20% and 75% of the stroke. Steam, in contrast to water, can expand after
cut-off and still convert much of its energy into piston force. In doing so, it loses
much of its heat which helps to limit the pressure drop. However, a cut-off at about
30% of stroke is the smallest practical setting, as below that the outlet pressure is
too low for a good exhaust and also the engine starts ‘banging’. If even less power is
needed, the steam inlet rate is best reduced with use of the regulator. The valve gear
is so designed that it only starts opening at about 20% cut-off. A cut-off of 75%
would only be used to start the train, together with careful control of the steam with
the regulator. For this description, a cut-off of 50% (Midstroke, Fig 39b & 31b) was
chosen - it is well within the normal working range. At this point the piston valve
must quickly close the cylinder port to the inlet steam but not yet open it to the
exhaust. This is why a valve head must be at least twice as long as the cylinder port
opening. It should be noted that when the piston is in the midstroke position, the
crank pin is still a little distance from the bottom dead centre due to the angularity
of the connecting rod. In the Cls 23 it is only about 2º - nothing to worry about.
The stroke is therefore 50% and rotation 88º in this case; the steam starts to expand
- there is no opening to inlet or exhaust.
3. (Fig 39c, apr. 95% stroke, 160º rot.) The steam expansion comes to an end -
the outlet to the exhaust is starting to open. The pressure, already low, drops further
to the blast cap pressure, which depends on the steaming rate. An average pressure
of 6 - 8 lbs/sq in. is common for normal working conditions. (The pressure varies
considerably at slow speeds - there are four ‘beats’ per wheel revolution - but as the
speed picks up the variation becomes very small)
The opening to the exhaust is maintained as the piston reaches the end of its stroke
(BDC, rotation half a turn = 180º) and carries on with the return past midstroke (rot.
just past top dead centre) until it has completed about 75% of the return stroke (rot.
about 300º). The pressure average remains low and equal to the blast cap pressure.
4. (Fig 39d, 75% stroke, 300º rot.) The port closes to the exhaust, while the inlet
remains closed. This is the start of the pre-compression part of the cycle. In this
part, the remaining steam is compressed to a pressure close to boiler pressure and
the temperature also increases. It serves two purposes: From the mechanics point
of view, the increasing pressure helps to retard the piston and rods which is
necessary at the end of the stroke, reducing the load on the bearings. From the
thermodynamics side, bringing the remaining steam to boiler steam conditions just
before the boiler steam inlet opens, improves the energy efficiency of the cycle.
5. Just before the end of the return stroke, the port is opened to the boiler steam
and we reach the start of the cycle as described in Point 1.
36
As the cylinders are double-acting, what happened in the front of the cylinder has
to be repeated at the back of the cylinder, but half-a-cycle later, ie about 180º
rotation later. This is ingeniously managed by repeating the front piston valve/port
details at the back head of the piston valve, but as a mirror image of those at the
front. It automatically leads to the required result.
6.5.3 The Piston Valve and Rod
The piston valve (Fig 30 I and inset of I x2 scale) consists of two cylindrical steel
Heads with cast iron outer Bull Rings, bolted onto the Valve Spindle rod. Their
position along the rod can be slightly adjusted with shims during assembly to
match the Steam Ports machined into the Steam Chest Liners. The usual proportions
are such that with the piston valve in the centre of its stroke, as shown in Fig 30,
the outer edges of the two heads should be in line within 1/16”with the outer edge
of the steam port, when the engine is at its normal operating temperature. I was
told in the SAR Workshop, Pretoria, that the rod expands about 1/32”in length
when it reaches that temperature and this should be taken into consideration
during cold assembly and final adjustment of the valve gear. This gives one some
idea how precise one has to be when working on these big brutes!
This design has one big advantage over the older flat sliding valve (not shown)
and that is that the inlet steam is between the two heads: the pressure load of
about 22 tons outward on the two heads is balanced by the rod between them. No
big force is needed from the valve gear to move the heads backwards and
forwards. Leakage of inlet steam past the heads to the exhaust is limited by a set
of three or so cylinder rings fitted into grooves on the bull ring. A gland is also
fitted around the rod where it leaves the steam chest to be pinned to the
Combination Lever (Fig 30K) at the Valve Spindle Crosshead (Fig 30L).
6.5.3 Managing the Valve Spindle Movement
If we again look only at the front part of the cylinder with the engine running
forward, we note that three of the four port opening or closing functions occur
close to the beginning or end of the stroke and that they are at fixed positions
relative to the wheel rotation. (Only one function, the closing of the inlet steam,
needs to be adjustable.) It follows that one of the ‘fixed’ drives needs to shift the
whole valve head assembly close to the front of the liners when the piston is at
FDC, and close to the back of the liners when the piston is at BDC. This is the
function of the combination lever which is coupled to the crosshead and therefore
is exactly synchronised with the piston travel.
What is still needed is a drive that can move the valve heads still further from the
position where they were brought by the combination lever, to open and close the
ports as needed. The drive mechanism that can do this is the Eccentric Crank (Fig
30M), which is bolted to the protruding end of the crank pin (Fig 30 I) - it is the
only place it can fit without fouling the connecting and coupling rods. Its Crank
37
Pin trails the connecting rod crank pin by approximately 90º in forward motion -
the exact value is determined in the Locomotive Design Office on a Model of the
Walschaerts Valve Gear. All the critical items are adjustable which enables the best
design to be established by intelligent trial-and-error. The move started by “MM”,
was to space the crank so as to obtain as large a ‘throw’ as practical from the
eccentric crank pin. This makes for rapid opening and closing of the steam ports
which improves power and efficiency.
This drive needs to be ‘managed’ to, firstly, enable the cut-off to be adjustable by
the driver. This is where the Expansion Link (Fig 30N) comes into play (or rather
‘work’). It was already used be Stephenson around 1825, but his link was driven by
eccentrics which cannot easily supply a large throw, so his gear became obsolete
on the SAR in about 1910 when larger locomotives were needed. The first local
locomotive with Walschaerts valve gear was introduced around 1896 on the
NZASM with the ‘46-tonner’ class from Holland - the Continent started using this
Belgian design long before the British could be converted from their traditional
Stephenson Link Gear.
How is the cut-off adjustment done? The expansion link is supported by centrally
located pins from the frame, around which it can swing - clockwise while the
driving wheel rotates from top dead centre to bottom dead centre and anti-
clockwise while the wheel rotates further from BDC to TDC. In the expansion link
there is a curved slot into which is fitted a Die Block, which can slide up or down
the link slot as the Radius Rod (Fig 30P) is moved up or down by the driver. The
drawing in Fig 30 shows the valve gear in the central position where the action of
the die block is not shown; refer to Fig 38 of my model which shows the valve gear
set at about 60% cut-off in forward gear. It shows how the bottom of the expansion
link is in the full forward position, the die block is halfway down the expansion
link slot and that the valve spindle is pushed far forward so that front valve head
still has the steam port open to the boiler steam while the back valve head is open
to exhaust.
Managing the cut-off is simply done by lowering the die block with the lifting link
to obtain a longer cut-off.
The second management function that is needed is to be able to run in reverse.
This is done by lifting the die block past the centre to the upper half of the
expansion link: again, the further away from the centre the die block is lifted, the
longer the cut-off.
Finally, some further observations on the proportions of the valve gear. Refer to
Fig 30 where the valve gear is in neutral and the piston at midstroke: the valve
heads are now dead central; the combination lever needs to be exactly vertical.
The aptly named radius rod length from pin to pin centre must be equal to the
radius of the expansion link slot. When the piston is at the end of a stroke, and the
38
die block is moved up and down, the top of the combination lever must not move
horizontally ie the valve heads must stay in their position.
A last point is that as the valve gear has of necessity to be on a plane further out
than the connecting rod and the cylinder centre, the valve spindle centreline is also
about 6” outward of the cylinder. This restricts the diameter of the valves to about
half that of the cylinders otherwise the steam chest would foul the loading gauge.
6.5.5 Cylinder Protection under Running Conditions
Under running conditions other than pulling the load, further devices are needed
to ease the motion and prevent damage.
On starting from cold, the first steam to enter the cylinders is partially condensed
by the surrounding metal and the cylinders, etc contain air. To prevent damage by
compression of the water at the end of strokes, Cylinder Drain Cocks at the bottom
of the cylinders and at both ends can be opened from the cab. They are opened as
the locomotive starts (or if priming of the boiler is suspected), leading to clouds of
steam erupting from them for the first few turns of the wheels. Quite a sight!
When the locomotive coasts downhill, other devices come into play. On the
outside of the cylinder steam chest at centre, a large Snifting Valve is fitted. It is a
valve which closes when steam under any pressure is in the steam chest.
However, when the locomotive coasts downhill, the valve gear is put into full
forward gear and the regulator is closed. The pistons now act in suction for part of
the stroke and would pump in smoke and trash from the smokebox, were it not for
the snifter. It opens to the outside air if the pressure drops below atmospheric and
brings relief.
The two Bye-pass valves on top of each end of the steam chest have an additional
function, ie they automatically relieve the excessive pressure built up by the
compression stroke of the coasting locomotive.
The last addition is the Drifting Valve operated by the driver. It allows a small
amount of steam with its quota of oil to be released to the cylinders, usually used
when drifting. The main function is to keep feeding some lubricating oil to the
moving pistons and to prevent the cylinders from cooling down too much. Careful
drivers also use them shortly before they start with the drain cocks open after a
long halt, to preheat the cylinders. I have even experienced it used to start a
passenger train smoothly.
6.6 Frame, Suspension and Curve Handling
6.6.1 Frame
The function of the Engine Frame of the locomotive is to keep the various moving
parts in their correct position even under the high forces experienced under
39
running conditions. Before 1930 most of the SAR locomotives had Plate Frames (Fig
40a) made of two steel plates about 1” thick and maybe 3’6” high, bolted to spacers
to keep them at the correct distance apart. Cylinders were of cast iron bolted onto
the frames. These frames were adequately stiff in the vertical direction but were
too flexible in the transverse direction, ie to resist the forces around curves,
particularly for heavier and longer locomotives developed from about 1925
onwards.
Bar Frames (Fig 40b) now took over. They were machined from about 5” thick bar
steel, maybe 2’ high. The advantage was that there was more room for a larger
boiler, firebox and cylinders, and that the coupling force was now in line with the
centre of the frame - no vertical bending. But the cylinders, etc had still to be
bolted to the frames. A real disadvantage was that now the vertical stiffness
proved too low, but that problem was well solved by fixing the boiler to the frame
as shown in Fig 40b. The front of the frame with the attached cylinders was firmly
bolted to the smokebox, but the firebox rested on slides which accommodated the
expansion of the boiler of about 3cm from cold to hot. Along the main part of the
frame it was attached to the boiler by vertical support plates which could absorb
the expansion with little stress but gave firm mutual support in the vertical
direction between boiler and frame, leading to an extremely stiff vertical assembly.
The final development was the introduction of the Cast Steel Frame (Fig 41), a
superb solution made possible by the development of the technique by the General
Steel Castings Corp. in the USA during WW2, to cast war tanks in one piece. The
system has big advantages: because the steel can be placed in any position and
any thickness, an extremely light but strong and rigid frame can be made which
incorporates the cylinders, steam chest, smokebox saddle, axle box horns and the
cross stays all in one piece. They were introduced with the Cls 24, used on the Cls
25 and its condensing tender, as well as the GMA/M. They gave excellent service.
6.6.2 Axle box Guides and Suspension
The Axle boxes of the coupled wheel sets fit into the Horn gaps (Fig 40b) of the
frame. The axle boxes are subjected to backwards and forwards forces by the
piston and cylinder, which they need to transmit to the frame with as little
‘banging’ as possible. At the same time they must be able to move vertically
where the track is uneven, eg over points or when the locomotive cants round a
curve. It means there must be a little play between axle box and frame and that
wear will take place. To provide for these demands, adjustable Shoehorns much
broader than the horn are fitted to the frame as shown in Fig 42. An American
design of a spring-loaded self adjusting shoe horn was successfully tried out on
15CA No 2828 and was subsequently used on all the Cls 25 engines, eliminating
regular adjustment by the running shed staff.
40
A clamp, called a Hornstay, is fitted under the horn to close the gap, thus
preventing the axle box from dropping out under extreme conditions, but more
importantly, to strengthen the frame against vertical bending.
In the modern motorcar, an independent spring system for each wheel is taken for
granted - the exact opposite works best for the locomotive. Why? Firstly, the
maximum wheel load prescribed from the track’s point of view is critical - only a
small fraction of extra load will lead to considerable extra wear, particularly when
negotiating points which are inherently bumpy. So the demand is that if there is a
slack or a bump in the track, ensure that the change in wheel load is spread as far
as possible to the other wheels. This led to the introduction of the Compensated
Spring Gear (Fig 43). Each axle box has its own spring, but the springs are not
directly attached to the frame: they are hung by Spring Hangers from Compensating
Beams which in turn are supported at their centre by the frame. The system is even
extended to the bissel bogie under the firebox. Only the first and last hangers’
ends are pinned to the frame. If any wheel rides over a bump, most of the extra
spring compression is transferred and distributed to the other wheels, thus
limiting overloading onto parts of the track.
Note however that the compensation does not extend from one side of the
locomotive to the other: Modern locomotives are already prone to roll due to their
high centre of gravity and a very large overhang over the track: a 10’ broad
loading relative to a 3’-6” track gauge. Cross Compensation would make the roll
much worse
6.6.3 Negotiating Curves
One of the most exciting events when one first joins the driver and fireman on the
footplate is when the locomotive has picked up a nice turn of speed along the
straight and heads for the first fairly sharp turn to the left. You are behind the
driver on the right and as the curve comes close he shouts “Hou vas!” and
suddenly the track disappears to the left - but the locomotive is still charging
straight forward- - - . OH NO! WE are going to derail - I knew he was going too
fast. Then Bang! The front of the locomotive swings hard to the left and
disappears from your sight as you get flung to the right and hang on for dear life
to the handrail. Phew, we made it after all, Praise be to God! By the time it has
happened ten times you take the curves hands free and wonder what all the fuss
was about - well, not quite, it will always be exciting.
So how does it all work - how can you fit a locomotive with a 37’ long wheelbase,
of which 16’-6” (the four coupled wheel pairs) is fixed, onto a sharp curve? After
all, on the 300’ radius curve, the sharpest your Cls 23 will encounter regularly on
the Hex River Pass, the curve will be 7” away from a 37’ long straight line (the
engine wheel base), and 1½” away from the line between the first and last coupled
wheels. The answer is, it won’t fit, (Fig 44A), unless you do several of the things
listed in Fig 44 B.
41
Let us first look at the locomotive:
a) The Front Bogie and the back Bissel Bogie are made to shift sideways. The front
bogie is kept in its central position on a straight track by two springs attached to
its turning pivot and supported at their ends to the frame. When the bogie enters
the curve, it turns enough to keep the wheels in the right direction, but most
important, the springs are pressed from their central position and start to push the
engine frame sideways, near to the front of the locomotive. This starts the slewing
action needed to negotiate the curve without too much sideways force on the first
coupled wheel. It also explains why the locomotive is about a third of its length
into the curve before it really starts curving itself. The Bissel bogie also has a
lateral spring system rather like the front bogie. In some of the last locomotives
there are also roller supports on the bissel axle boxes which increase the weight
load on the outer axle box with a corresponding reduction on the inner axle box, to
reduce the tendency for the outside wheel to climb over the rail as shown in Fig
44A.
b) The Coupled Wheels can be adapted as follows: the leading wheel pair’s axle
boxes can be given an additional lateral clearance in the horns of 1” either way
(Fig 44 (2)), and the third wheel pair (which tends to run close to radially on a
curve), is made flangeless and , if necessary, slightly broader than normal(Fig 44
(4)).
Note: The calculation of the position of a locomotive’s wheels on a curve is fairly
complicated, but it is well explained in “MM”s ‘Annale’, Ref 8. Copies can be
made available on request.5
Regarding the track, the Chief Civil Engineer collaborated to incorporate the
following changes as standard practice:
c) The rail gauge is slightly widened on sharp curves up to a maximum of ¾” on
curves with a radius of less than 700’ (Fig 44 (1)).
d) A Checkrail (Fig 44 (5)) is fitted at the same height but next to the inner rail to
check the sideway’s movement of the wheels when the flat inside of the flange of
the inner wheel rubs against the checkrail. This limits the tendency of the outer
wheel of a wheel pair to climb over the outer rail when it is forced at an angle
against it.
e) Super elevation (canting) of the track is applied (Fig 44 (3)) to the extent that the
outer rail is 4½” higher than the inner rail.
One last comment: Scheffel’s brilliant invention at this time to make four-wheeled
bogies negotiate curves with both the axles in a radial direction did not have an
equivalent for tender 6-wheeled or engine bogies. So we shall leave it at that.
5 Should there be interest in this paper it could be published as a special issue of ULOLWE - HBH
42
6.7 Lubrication
Lubrication will always be remembered as the hallmark of the engine driver:
whenever the train is stopped for a period, we see the driver checking around the
locomotive, oilcan or grease gun in hand - the mere fact that it had to be done so
often shows that it very often was a problem. In fact, the final limitation to the
steam locomotive up to the Cls 23 lay in its broader sense, in friction. The problem
lay on the one hand, in not having enough friction between coupled wheels and
rail on starting or emergency braking, and on the other, in often having too much
in the overloaded rod, crosshead and axle box bearings or even more so, between
piston and cylinder - the Hot Box Syndrome.
Rod bearings have been dealt with, but not piston sliding in the cylinder. Up to the
Cls 24, cylinder lubrication was done by feeding a small amount of boiler steam
over a container with boiler water and engine oil (all at boiler pressure) and letting
the oil float to the top of the water, drop by drop, where it was swept away by the
steam to the cylinders. The flow rate had to be regularly adjusted by the driver
peering through small, often murky glass portholes. The problem was not solved
until mechanical lubricators were used on the Cls 25 and the GMA/M. Now there
certainly was enough lubricant around - or was it too much? (Fig 45). That
combined with the increased or complete use of roller bearings, reduced friction,
vastly improving the reliability of steam locomotives.
The story is told how one of the new Cls 25NC’s was standing unmanned on the
level at Paarden Island, Cape Town’s running shed, one very windy day. Loco and
shed staff was used to leaving locos without any brakes on, as there was enough
friction to keep them quiet on the level, but in this case the South-Easter was at its
spectacular best and when the foreman looked out, the locomotive was slowly
beginning to move and picking up speed. With enough running and yelling, he
managed to get the staff to grab some scrap sleepers and to throw these onto the
track between the wheels to eventually bring it to a stop right down the yard.
Another regulation was put on the books by next morning.
Usually it is assumed that a locomotive of the Cls 23 type has a rolling friction
when in a running condition of at least 4½ lb/ton. If the wind touched 60 km/hr, it
would only move the cls 25 locomotive if its friction was as low as about 2½ lb/ton.
6.8 Tender
The tender’s main function is of course to carry the water and coal supplies in a
way accessible to the loco. If the grate is mechanically fired, the tender must also
house the screw conveyor and the steam engine to drive it (Fig 46). Quite
important is that it was the only part of the locomotive to have vacuum brakes in
the pre-war years. Drivers did not like to make use of the steam actuated brake on
the engine; it had almost an on-off type of action. After the war all engines also
had vacuum brakes, which operated together with the vacuum brakes on the rest
of the train.
43
The coal ‘bunker’ on the modern tender was shaped with both sides and the end
plate sloping as can be seen in Fig 2. This made it easier for the fireman, it was not
necessary to Trim the coal except when the last little bit was needed. The
Mechanical Stoker’s layout of a Cls 25 can be seen in a sectional drawing in Fig 46.
Of interest is the simple but effective way of feeding the coal to the Conveyor
without clogging it: the top of the conveyor slot is closed by a set of movable Slides
before the coal bunker is filled with coal. The coal can be easily hand shovelled to
start the fire and when the steam pressure is sufficient to start the conveyor, the
fireman takes a rod with a claw at its point, sticking the claw into a hole in the
edge of the first slide. With a smart pull it is moved forward opening a gap
through which the coal in the front of the bunker starts pouring in. It stops when
the coal heaps up to the slot at about 45º as shown in the drawing - there is enough
coal to feed the screw without clogging it. It works well, except that the coal is
crushed too much for efficient burning!
The screw with coal moves towards the firebox door up an Intermediate and an
Elevator Unit (pipes with swivel and telescopic joints). The coal drops onto a
Distributing Table just inside the firebox. The fireman has charge of a set of five Jet
Valves which actuate the jets in the table which blow the coal into the centre or any
of the four corners of the firebox. He also has a valve which controls the speed of
the engine driving the conveyor. It requires a lot of practice to handle it well.
In section 6.4, mention was made of the advantage to couple the tender so directly
to the engine that the two would act as one body as far as damping the backwards
and forwards oscillation of the locomotive is concerned. Where the coupling is
fitted, is shown in Fig 46 and the details of its construction in Fig 47. At the
bottom is the Intermediate Drawbar, a solid bar with an oblong hole at each end
through which the two coupling pins are fitted. Before the pins can be inserted,
the Compression Spring above it has to be compressed by another locomotive or
heavy jacks. The spring is strong enough to resist the compressive part of the
oscillation cycle, ie the drawbar remains solidly coupled. Only during shunting or
coupling operations can the compressive load become so high that the load on the
drawbar drops to nil and the engine and tender can move a bit closer within the
limits of the oblong holes in the drawbar. There is therefore no danger of the
drawbar being buckled or of the engine being slewed to one side. The design also
accommodates the relative lateral movement between the back end of the engine
and the front part of the tender when, for example, they negotiate the S-shaped
track on moving from a sideline to the main line. The Cushion Buffer Button which
transmits the compressed spring’s load to the Engine Drag Box can slide over the
drag box face without losing the spring load. You become aware of this when you
see the tender moving about 6” to one side and then the same to the other side
while peculiar groaning noises come from under your feet, as the loco negotiates
the points to the main line. (This is in addition to the bumping noises from the
wheels as they pass over the gaps in the points). The cushion effect also helps a bit
to dampen slewing of the locomotive.
44
6.9 Vacuum Brakes
I still have memories as a child of going with my parents by train down the Hex
River pass at night. My brother and I shared a coupé. My dad had explained to
me about the pass that it was very steep (It was before a gradient of 1 in 40 meant
anything to me) with lots of sharp turns, and that we would pass a memorial for
the soldiers who had died in a train derailment in 1914 because the brakes had
failed. This had me very worried but I was too scared to say anything - I was
however determined to stay awake and to make sure that we came through the
pass unscathed. One thing that I remember clearly as I peered through the
window is seeing the whole train crawling down a curve with the locomotive
headlight showing the way, but then an unexpected wonder: a brilliant shower of
sparks around every wheel of the coaches: it made me completely forget the
memorial and the dangers. In later years I learnt that the brakes were cast iron
brake blocks pressed hard against the steel wheel rims by the Vacuum Cylinders,
and that during a long application the blocks got so hot that sparks could form.
Incidentally the coefficient of friction reduces under those conditions, so that the
driver had to apply the brakes a bit harder. Nowadays composite blocks are made
of a plastic and filler mixtures (Asbestos no longer allowed!) which has a higher
friction and a longer life - they still act onto the wheel rim. The Blue Train is an
exception: it has disc brakes, smoother and quieter, but probably more expensive.
While we are still close to the Hex River Pass, by the time I was a student on my
way to Maties, I became aware that on the way down that there is a section of the
track between the steep sections which was level: the reason is to give the driver a
section where he could release the brakes and steam lightly. The brake release was
called the Regeneration of the Vacuum in all the vacuum cylinders. The brake force
comes from a cylinder with a piston (Fig 48). When the brakes are off, there is a
partial vacuum on both sides of the piston and the piston drops to the bottom of
the cylinder. This partial vacuum is generated by an ejector in the locomotive’s
cab and piped by the Train Pipe along the full length of the train. To apply the
brakes, the driver allows some air to enter the train pipe, the vacuum becomes
smaller and this lower vacuum is piped to the bottom of the cylinder only. The
piston is pushed up which applies the brake.
The top of the cylinder is also connected to a ‘reserve’ Vacuum Chamber so that if
there is a slight leakage past the piston in spite of the Rolling Ring seal, enough
vacuum is retained to handle the brakes. However, if the brakes are applied hard
for a long time such as down the Hex River Pass, problems might arise (Remember
the Memorial!) Hence the level section halfway down the pass.
The vacuum brake is a British tradition; it performs adequately but because the
pressures are relatively low (about 10 lb/sq in) the cylinders have to be large. With
the Continental system using compressed air, much smaller cylinders are sufficient
and response times are much shorter, but far more attention is needed to ensure
that the train pipe joints are well made and correctly tightened.
45
This brings to a close the summary of how the steam locomotive worked. One is
painfully aware that it is not complete and also, that for many readers it will be
confusing - too many new ideas compressed into too little space. Try to
concentrate on the little incidents on a second reading and skip the engineering
details!
Now for some memories of several personal experiences in trying to solve
problems experienced on the SAR and a private Narrow Gauge line to Port
Elizabeth, while I was in the CSIR doing research in the Strength of Materials field.
7. Problem Solving for the Railways - Personal Experiences
During the period 1954 to 1964 while I was at the CSIR in the Strength of Materials
Division of the NMERI there were several projects on our list that originated from
railways. They all had some interesting aspects which I would like to share with
all ‘Friends of the Rail’.
But first of all let us try and recapture some of the background of those times:
those were the days before computers had developed to the stage that engineers
could use them as day-to-day tools to calculate exactly what the stress pattern was
in their designs. With slide rules and log books we could only do so for very
simple shapes. We were just beginning to appreciate that holes, sharp notches or
rapid changes in cross-section caused much higher stresses than the mean values
we calculated - they could lead to early failures, particularly under repeated
loading. Let us remember how the first jet-powered airliners, the Comets, had
several disastrous accidents and had to be scrapped round about this time. The
cause was the explosion of the fuselage which was kept at close to atmospheric
pressure when it flew at heights approaching 30 000’. The designers had
unwittingly used rectangularly shaped windows in the fuselage, and did not
appreciate that extremely high stresses acted at the square corners when the cabin
was placed under this pressure. Cracks formed after a relatively small number of
cycles, triggering the explosion after a few years of service.
It was my choice to concentrate on experimental stress analysis techniques to
determine actual stresses on models or prototypes, using the capital that became
available to invest in repeated loading testing machines with loading capacities up to
100 tons. Particularly valuable was the recently developed SR-4 Strain Gauges and
their Multichannel Recorders. Fig 49 shows strain gauges ‘cemented’ (The generally
accepted American term for ‘stuck on’) onto rails. The strain gauge is very simple:
it is a flat coil of thin alloy wire wound around a paper slip and cemented between
two more thin sheets of paper (Fig 50). Their resistance was usually 120 Ohms.
When the gauge was stuck onto a metal object which was then subjected to stress,
the object would strain accordingly and so would the strain gauge in the direction
it was cemented. (If you did not know in which direction the main strain would be,
you used a Rosette of strain gauges close to each other, usually with an angle of 45º
to each other. From those three readings you could calculate in which direction
46
the main strain was and its magnitude). The open secret of the gauge was that as
the whole gauge strained with the metal below it, the wire did the same: if, for
example, it was a tensile stress/strain, the wire would become accordingly longer
but also smaller in diameter, the overall percentage change in its electrical
resistance being usually twice as much as the percentage change in strain. We
called this a Strain Gauge Factor of 2. An important development at that time was
made by the electronic engineers who developed compact portable instruments
that could comfortably measure strains with an accuracy of 5 parts per million! (If
you had a strain gauge cemented lengthways onto a ¼” (6mm) diameter steel rod,
you could reach this 5 micro-inch per inch reading if you pulled it with a force of
only 7 lbs). Another big advantage of these strain gauges was that they could be
connected electrically in ‘bridges’ so that one could get a reading of the average of
the two, or of the difference between the two. Returning to the ¼” steel rod, if two
gauges were cemented lengthways onto the rod, but exactly at 180º to each other, it
would accurately measure the tensile load on the rod even if there was superimposed
bending or eccentric loading. Similar ‘tricks’ could be used to measure only the
amount of bending (by connecting them differentially) or twist (with gauges
cemented at 45º to the longitudinal axis), etc.
If these ‘bridges’ were cemented onto a component, to be tested under running
conditions, the readings from the bridges could be calibrated beforehand by
applying known loads to the component in a testing machine. When the
component was being tested in practice, it would be convenient to take the
readings from these different bridges so that clarity could be obtained as to what
conditions lead to maximum loads and how they relate to each other in time and
magnitude. The detail stress analysis in the ‘danger’ areas at ‘notches’ or changes
in section can then subsequently be obtained accurately in the laboratory, with the
component back in the testing machine and some strain gauges in the critical
sections.
It takes some time to master the art of the strain gauges: choosing the right type
and length - the smallest are more liable to problems - preparing the surface for
cementing - which of the four cement types would be most suitable for this job -
which recorder - what speed and sensitivity settings, etc., but the results are worth
it. Without them, the problem of the connecting rod fractures on the first Cls 25
locos dealt with in Section 7.1 would not have been solved.
7.1 The Case of the Fractures of the Unbreakable Connecting Rods
Connecting rods were always prone to failure, as was already mentioned at the
end of Section 6.3, so when the Cls 25 had to be designed, the SAR was very happy
that Murray Franz became available to improve the 15F connecting rod design:
they would both be of the same length of 7’ 5” between pin centres and the loads
would be only 7% more on the Cls 25. Murray had just returned from England
where he had worked on the strength design of aircraft: he knew far more than
any of us did in 1951 about stress analysis and all were happy that now, for the
first time, there would be an unbreakable connecting rod on a SAR locomotive, the
47
Cls 25. The locomotives were placed in service during 1953. The first failure took
place in Sept 1954 and in the following 12 months another 5 followed. The
Metallurgy Section of the SAR checked the steel - it was a Mn-Ni-Mo-Si steel (EN
13), hardened and tempered - and found it in order. The position of the start of
the fatigue failures is shown in Fig 51. What was most unusual was that the
fatigue failures all started on a fillet between the flange and the web of the rod,
three near the big end and three near the small end. The only type of loading that
causes a maximum stress in such fillets is torsion of the rod as a whole, a type of
loading not previously taken into consideration in the design of a connecting rod.
A first prognosis was that torsion was the culprit, that it came about because of
tilting of the locomotive over points or curves and because these new-fangled
Timken double-taper roller bearings had no play to absorb this tilt. What confused
the picture, however, was that not all of the cracks were at an angle of 45º to
centreline as would be expected if there was a dominant shear stress. The matter
was urgent so it was prudent to combine the SAR team with the CSIR team to solve
the problem - we had suitable big testing machines in our laboratory. A spare
connecting rod was delivered to the laboratory even before the contract was
signed and my team got stuck in to cement all the strain gauges at the right places.
We put in bridges along the length of the rod to measure longitudinal, lateral
bending, vertical bending and torsion loads - three of the latter to be able to check
one against the other or if there was a failure in the gauges: life is tough on a steam
locomotive. The 6 bridges were calibrated in the testing machine. We could just
fit the rod in the testing machine for the longitudinal load, but how do you apply
torsion? The answer lies in an X, just visible in Fig 52. (Sorry for the poor quality
of the reprint, it was all I managed to get from the CSIR archives of reports. The
original photo was good but the negatives remained with the CSIR and they are
not readily available any more). The drawing in Fig 53 makes it clearer. While the
two diagonal beams press down onto the rod clamps and twist the rod, the twist
deflection is measured by four deflection gauges fixed to a separate pair of
unstressed clamps. The twist load is calculated from the compression load shown
by the testing machine and the bridge output read from the strain gauge meter at
the same time.
Gouws of the SAR and I travelled with the calibrated rod stowed on the
Dynamometer Coach, No 60, down to Touws River where Engine 3508 was ready
for the rod. Engine 3508 had already developed two flawed rods with only 130 000
miles service. The biggest problem with the strain gauge tests was connecting the
large number of leads from the strain gauge bridges on the rod to the multi-
channel recorder made available for the test by the SAR. The best we could do was
to pull a rubber pipe over the leads and to clamp it to the combination lever on its
way to the running board and back to coach 60. In practice, it did not last longer
than about half an hour with the loco working hard before some of the wires
started failing. (Why is it that a specialist on fatigue failures like me, experiences
more fatigue failures with his own equipment than anybody else?) Anyway, we
did manage to get all the recordings we needed within about two weeks and could
48
submit a clean report at the end of all the tests. Even the highest stresses were well
below the fatigue strength of the rod.
The highlight of the test was my first opportunity to be on the footplate of a Cls 25
locomotive and experience the thrill as the giant pulled away at full power,
picking up speed against the gradient like I never experienced before. I did miss
the sharp exhaust beat as it was a condenser but the fire roar and the vibration was
there even better than on the Cls 23. It was also the last trip I had on the footplate.
The main results of the tests were:
• Yes, there was a significant torsional load on the rod when the locomotive cants:
the biggest effect was when the locomotive pulled a full load over the set of
points running from a branch line to the main line. At a speed of about 24 mph
(The allowable limit is 20 mph!) the cant was almost 2º either way and when the
locomotive was pulling hard the rod was subjected to nearly the same degree of
twist.
• The torsional twist was so high in spite of play in the crosshead and bearings, as
the high connecting rod push or pull loads cause the play to be taken up by
wedge action: an end load of 94 000 lb was measured on the connecting rod!
• The maximum stress was found with the loco pulling hard over the set of points
and was not in the fillets where the flaws had started, but on the flanges near
the big end, due mainly to the combined effect of end load and lateral bending
due to about 0,35” eccentricity of the end load. To a lesser extent there was also
stress due to cross bending under torsional twisting (The eyes at the end of the
rod restrain the I-section from twisting in the normal torsion way: instead, there
is some cross bending stress on the flanges next to the eyes). From where the
eccentric loading? It is not easy to believe, but it was clearly shown to be due to
elastic bending of the crank pin and the whole wheel assembly, solid as they
might appear - well, 47 tons is a big force.
• The maximum stress of 25 000 lb/sq in. was in any case considerably less than
the expected fatigue limit of over 30 000 lb/sq in., so Murray Franz’s design was
vindicated. It seemed that stress was not the primary cause of the failures.
Just imagine how I felt when these results became clear. Where was my mistake?
I spent several sleepless nights checking and rechecking all the calculations, and
was at least thankful that the three torsion bridges were consistent within a few
percent. Gouws and I could not come up with any logical explanation, unless . . . .
Next morning I tackled my good colleague ‘JP’ Hugo, our metallurgist, and asked
him to please find something wrong with the material (in spite of Dr Reissner’s
conclusions), and slipped him one of the specimens of the failure. I had a guilty
feeling as I, being only 28 years young, did not like to risk asking the big bosses in
the SAR to approve of this step which was in any case outside my brief. Next day
JP turned up with a gleam in the eye and ‘borrowed’ another specimen. Within
two days it was clear: somehow the rods had been welded in the flawed fillet area
after its heat treatment, and before it was finally machined (no superficial sign of
49
any change in the metal - until you etched it). We as engineers all know that
welding highly stressed heat-treated steel is a disaster.
The finding was reported to the ACME Dr Douglas immediately via our boss Dr
Roux, leading no doubt to consternation that the SAR had not spotted the cause
but also relief that the manufacturer of the rods, Henschel und Sohn, would have
to rectify the fault. JP and I never had any direct formal recognition for the
solution of the problem from the SAR. What we did hear was that the slip had
taken place during a night shift machining operation at Henschel. To the milling
machine operator who had to mill the inside of the flange of the connecting rod, it
was a first experience that the flanges were slightly tapered and not parallel; also
that the rod was made from a heat-treated steel. He made a slip in milling the
flange and took a cut which was too deep. He seemed to pick this up soon enough
but about 10 rods were involved. He got his pal the welder to quickly fill up the
missing material and then re-machined the rods, without realising the damage that
had been done. All one can say is that the welder did a perfect job: no pitting or
slag inclusions to catch the eye.
One last thought: courses in Strength of Materials always start off with stress as
the culprit to be watched and that strain is caused by stress - strain is handy to
measure the stress. Here we have a case where a strain is the cause of a stress,
superimposed on the stress due to loading forces. One can speculate that the many
cases of connecting rod failures in other engines were due to this extra
unrecognised stress from the torsion. The natural reaction to the failure would
have been to ‘strengthen’ the rod by thickening the flanges of replacement rods,
which would reduce the tensile/compressive stress, but due to the extra stiffness,
would greatly increase the stress on the outside of the flange when the rod is
forced to twist through the 2º (Although stiffer, it will still not be stiff enough to
restrain the locomotive’s cant). It could perhaps also increase the eccentricity of
the end load and therefore increase the lateral bending stress. So the ‘stronger’
rod can be expected to fail quicker. As steam locomotives were on their way out
and no new locomotives were ordered after 1954, this aspect was no doubt never
followed up. However, the Cls 25/25NC locomotives were never fitted with
connecting rod safety straps!
7.2 Case II: The Fractured Blower Turbine Blades
The Cls 25 condensing locomotive, as the designation tells us, does not blow the
exhaust steam through the chimney to the atmosphere - it is piped to the oversize
tender where the steam is condensed in a large assembly of small copper pipes
arranged as the side walls of the tender. To ensure sufficient cooling of the pipes,
large fans are fitted as part of the roof of the tender - they draw air through the
side walls over the pipe nests. The fans are driven by a steam turbine driven in
turn by the incoming exhaust steam: The faster the steam comes in, the faster the
turbine and its fans run. A similar turbine is fitted into the smokebox to drive the
50
Blower Fan that draws the air through the grate and boiler and exhausts the smoke
through the chimney.
Within about 10 months of service 26 cases of failed turbines due to fractured
blades had been experienced on blower turbine rotors (Fig 54). The blades are
fitted into a groove machined into the rim of the disc. A sectional view of how
blades are carried in the rim is shown in Fig 54. The turbines run up to speeds of 6
000 rpm for the blower turbine, the centrifugal load reaching more than a ton per
blade and there is substantial vibration as well as shocks if there is priming, etc.
The blower turbines were all rebladed with blades with a core thickness of 14mm
(Fig 54 e) in place of the original 7mm. The alarm bells went off, however, when
the rebladed turbines had their first failure, again after only three months. This is
where the CSIR was asked to find the cause and suggest a solution. This involved
both Metallurgy and Strength of Materials. We came up collectively with the
following:
• All the fractured and cracked blades inspected had failed due to fatigue starting
in the fillet at the back (trailing) edge (Fig 54 d 7 e), which carries the brunt of
the centrifugal load.
• The material appeared in order.
• Fatigue testing the 14mm blade up to the centrifugal load was sufficient to start
a crack at the same position as found in the failed blades, within about 100 000
cycles. (This was an extremely long test: we could only use our new 30ton Mohr
& Federhaff load alternator at 30 cycles per minute.) This would amount to
about four years service on the locomotive if it was accepted that there were
about 100 cycles of full speed of rotation dropping to less than a third of full
speed (about 10 % of the centrifugal load) per day of service and for 250 days
per year. The failures occurred far quicker than that, showing that the other
factors were significant, but the point was that even if these factors could be
eliminated, failures would in any case lead to the demise of a generation of turbines
every 5 years or so in spite of the reblading with blades of double the root size.
• Stress analysis of the blades was difficult because of the small radii of the blade
root where the crack starts, but measurements with Stresscoat, a brittle lacquer,
and strain gauges of 1/16” in length, combined with data from the newly
published book, Stress Concentration Design Factors by R E Peterson, gave a good
estimate of the stress values to be expected for the two designs of blade. The
14mm blade is 11% heavier leading to a correspondingly higher centrifugal
load, the stress concentration factor where the cracks start is about 30% higher
and the tendency to ride on the back ledge is also higher, which taken together
leads to about the same stress in both the 7 and 14 mm blades! Fatigue tests
confirmed these findings.
Here again we find an almost classical case of how doubling the size of a component prone
to failure leads to no improvement in service life.
Release of the report on this investigation to the SAR, who promptly sent copies to
Henschel, led to an invitation - or could it be taken as an instruction - to visit
51
Henschel in Kassel, Germany. It was my first visit by air to Europe, flying in the
noisy old radial piston engined DC-7B, which needed its four stops along the way
at Salisbury, Nairobi, overnight to Khartoum watching the flames streaming from
the engine exhausts, then to Rome, before landing at Frankfurt after an exciting
flight over the Alps - 24 hrs all told. They picked up my remains and drove me to
the grand Schloss Hotel at Kassel looking down on the Schloss garden where a
large water stream was allowed to cascade down once every Sunday. Hundreds of
quiet, demure citizens gathered there to view the scene, then just as quietly
returned home afterwards. From the Schloss you could just see the border of East
Germany, maybe 10 km to the east. It was an elite hotel where I felt rather unsure
of my position but I did manage to make them understand that I would appreciate
a plate of porridge for breakfast.
Next morning the discussions started, led by Herr Prof. Dr.-Ing. Ehrenhaber
Roosen, chief designer of the Cls 25, and Herr Oberingenieur Hany. As soon as
they found that I could (sort-of) speak German that became the language of
negotiation. It was quite a struggle for me. Roosen contested my findings, Hany
being more careful. They won the first round when they pointed out I had quoted
‘Petersen’ when he really was ‘Peterson’ (p.37). They had found the book but were
not really interested. Roosen was strongly of the opinion that the problem lay in
priming when the drivers opened the regulator coming full speed downhill in
advance of a steep climb ahead. I agreed that there were factors over and above
the centrifugal loading but their attempt to strengthen the blades by doubling the
neck was futile as they increased the stress concentration. What could they offer
to improve the situation? I offered to sit with them to do the stress analysis.
In Roosen’s autobiography (Ein Leben für die Lokomotive - 1976) he mentions my
visit but does not say anything about my point of view, he only says that he made
the remark “half in desperation and half sarcastically, why don’t we fix all the
blades like the last blade to be fitted - with taper shank bolts”. The point was that
apparently none of these blades had broken so far, a fact of which I was not aware.
As I recall, it was Hany who came along with some taper pins maybe 4 or 5mm in
diameter, and who suggested that between every blade foot, a hole be drilled
through and reamed to a taper; then the taper pin be forced in and riveted over on
the other side (Fig 54 f). This would force the blades together so that vibration and
shock effects would be reduced, and how about the centrifugal load? From
Peterson it appeared that it would reduce the stress concentration by a factor of
two to three so I agreed that it would be most promising in spite of the thinner
foot. If they could make up a sample ready for my tests, I would take it back and
could give them an answer within about a week. They could also take the case to
Dr Gassner at Darmstadt who, from his publications, was in my opinion the best
authority on fatigue testing under simulated service conditions. This was accepted
so Roosen took me in his beetle to Gassner - what a clean, precise setup! Gassner
was a little careful and did not commit himself other than to say that he was
booked up and did not see his way clear to do such a test with his Schenck
machines which would take even longer than in my M & F load alternator. Roosen
52
was a good host by this time taking me for a round trip along the Rhine past
Wetzlar, the home of my Leica camera, before coming back to Kassel.
It was time to return but all the flights were booked up. Eventually Henschel paid
up and booked me in First Class! The weather had become quite bad but we took
off in any case and headed for the Alps. What a trip - we found ourselves in the
worst storm I have ever experienced during a plane trip. Everyone was strapped
down tight, including the flight staff and meals shoved back into their racks.
Lightning all around us, then FLASH/BANG! The lightning struck the plane on the
wing. Lights out for a while, but the plane kept going on its extremely bumpy
way, and then we gradually cleared the storm and found our way to Rome, where
we palefaces were shakily led to the waiting room. It took two hours to clear up
the mess and check the plane. Some of the shocks were bad enough to break off
the tops of glasses stowed in partitioned racks, but we could continue after some
minor repairs.
The final chapter was that back in Pretoria the Hany specimen performed well in
its fatigue test (Fig 54 b). This conversion was then done on all the blower turbines
with good results. Eventually somebody suggested using broader sheet metal
vanes welded to the rim and this was the final answer. Nobody said how such a
contraption could be balanced; this was probably after I had left the CSIR, I was
not asked to follow up the case.
Another aside: while I was there I picked up a general news letter from Henschel
jnr. to his staff, expressing his regret that it was necessary to reduce staff as the
orders for locomotives had dropped - they had started too late to change over to
diesels. So for them the writing on the wall was many years earlier than for the
SAR.
7.3 Rails
The story of Loubsers and Rails starts in about 1927 when my dad “MM” got
involved in the question of how the then main line rail of 80 lb/yrd should be
upgraded to what became the 96 lb/yrd rail (Fig 55). Apparently rails had been
found with cracks in the lower fillet. “MM” did some tests on a section of 80
lb/yrd rail and became aware of the high stresses when the rail is subjected to high
lateral flange loads as a locomotive rounds a curve, so he proposed that the web
be not parallel, but become slightly broader at the bottom and that the lower fillet
have a bigger radius. Otherwise it is a slightly scaled-up version of the 80 lb/yrd
rail. In some mysterious way the test rail piece found its way into dad’s workshop
after the tests - I still have it, it makes a good anvil.
In view of the damage caused by the wheels at rail joints, it was decided later to
convert from 40’ to 60’ long rails which could still be packed onto specially built
60’ long flat coaches for transport, thus saving a third on fishplate joints. The need
to cater for temperature driven expansion and contraction could still be handled.
53
By the time I landed in the SAR, things had changed a lot. It was already standard
practice to weld three lengths of rail together in the workshops using the flash-arc
process: two rails placed end to end at a time are gripped near their ends, while a
strong welding current source is connected to the two ends. The rails are pushed
towards each other until the electric arc starts, when they are moved a fraction
away from each other until the arc starts to melt the ends. Then the current is
turned off and simultaneously the two ends are quickly forced together with a load
of many tons. The rails are now firmly welded together, only a flash from the
molten steel shows where the joint is. This flash is easily machined away, leaving
a smooth joint with hardly a trace of where the weld was. Thus rails of 180’ length
became available. They could be transported a few at a time along the centre of
three of the 60’ trucks, but were only restricted as far as lateral movement is
concerned on the central truck; they were free to slide sideways on the outer
trucks when the train went round curves. The fatigue strength of these joints is
practically as good as that of the unwelded rail, provided that the correct welding
procedure is used. Only a fatigue test in repeated bending can readily check the
effectiveness of the welding procedure.
As the CSIR was the only laboratory that had fatigue testing machines of sufficient
capacity (Up to 100 tons on the Amsler pulsator), the SAR turned to us to do the
tests and link them with stress analyses as well as checks on the metallurgical
aspects by JP Hugo’s Metallurgy sub-division.
Investigations at the CSIR started with the fatigue strength of thermit welded rails
compared to the fatigue strength of the unwelded rails. The question was also
asked whether superimposed tensile or compressive end loads influenced the
fatigue strength.
A thermit weld is made by placing the rail ends to be joined close to each other,
then fitting a ceramic mould around the gap, filling the mould and gap with
thermite powder (a mixture of mainly fine aluminium powder and Fe3O4 powder -
also used in incendiary bombs). On ignition, a temperature of 2600ºC is reached
and the iron oxide is reduced to molten steel, which fuses the two rail ends
together. The outside of the weld is very rough with a sharp fillet (Fig 56). We did
not expect any good results. The tests confirmed this:
• The fatigue strength of the unwelded rail in vertical bending was 45 000 lb/sq
in. End loads had no significant effect on the fatigue strength.
• The fatigue strength of the thermit welded rail was only 25 000 lb/sq in.
Superimposed end load tensile stress of 10 000 lb/sq in dropped the fatigue
strength still further to about 20 000 lb/sq in.
• Stress analysis showed that the weld shape led to a stress concentration factor of
about 1,4 and the metallurgical examination of the weld also indicated defects
such as small cracks, shrinkage cavities, lack of fusion, and a poor structure.
54
The importance of these tests is that a clear answer as to the anticipated life of the
welded rail can be obtained within a few weeks instead of watching specimens
built into the track over a period of years.
Over the years, several types of rail and rail weld were tested in fatigue for the
SAR - it almost became a routine test, although we always kept a close watch for
any unusual evidence. One such an interesting observation is shown in Fig 56 b,
where a thermit welded old rail with a fishplate hole next to the weld was
subjected to bending while coated with brittle lacquer. It shows cracked lacquer
with diagonal lines around the hole in the web. This is due to shear stress which
occurs in a web when the rail (or an I-section girder) is subjected to bending. It is
common knowledge for engineers that a hole in a part subjected to a tensile load
has a stress concentration factor of 3. What is less well known is that under shear
conditions, the factor increases to 4! It explains why rails bolted together with
fishplates often developed these 45º cracks, particularly if the bolts were left loose
and the rail end was exposed to impact shear loads as the train wheels climbed
onto the projecting rail end.
Two more interesting facts were picked up during this work: the first is that the
temperature differences, to which rails are subjected between day and night in
areas of clear sky such as the Karoo, are far greater than one would expect. The
rail is clear off the ground and well insulated from it by the sleepers. In the
daytime, the sunlight can push the temperature of the rail up to about 40º higher
than the air temperature, while at night the bright steel radiates heat out to the
open sky and its temperature can drop to about 20º less than the air temperature -
it is by far the coldest body you will see as you look around you. That is why rail
sleepers have to be so well anchored into the ballast to handle the expansion and
contraction loads.
The second and last is the strange way that a long rail deflects as a heavy wheel
rolls over it, as shown in Fig 57. It is well known that a wheel depresses the rail as
it moves over it and the load is taken by the sleepers - most of it by those closest to
it. What is not so well known is that further along the line, there is a marked
tendency for the rail to lift up over a short distance. The best way to accept this
apparent contradiction is to look at rail sleepers and imagine how they have to
push their part of the rail up to support the wheel’s weight. In fact, if it were a
short rail, the ends either side of the wheel would bend up considerably and point
over the horizon. But as it is a long continuous rail, the further extension of the
rail eventually pulls the rail back to its normal height. To put it another way, if
you want a warning signal to tell you when the first wheel of the train is coming,
you can put a light switch on the foot of a rail - the first indication that you would
get is when the switch is pushed up. Incidentally, the same happens to our made
roads. Failure of the concrete or tar roads is to some extent due to the tensile
stresses induced ahead of particularly heavy vehicles. Concrete is far happier to
handle compressive stresses. We are now far away from the subject of rails, so it is
time to stop.
55
7.4 Dynamometer Tests on the Narrow Gauge Railway
Why do dynamometer tests on a narrow gauge (NG) railway line at all, and if so,
why ask the CSIR and not the SAR to do it? Well, the NG line concerned was the
private PPC Company’s line from their lime mine near Hankey, to their cement
works in Port Elizabeth. They (George McEwan) did ask the SAR to do it, but the
reply was that they do not have a NG dynamometer coach, maybe the CSIR can
help. And why the test at all? They needed new and bigger engines and were
opting for a diesel but did not have the data to specify what was needed, so could
we help? Yes, we would love the challenge and got stuck in.
What is needed for such a test is to record the locomotive traction force (Or at least
the drawbar force, as was done with SAR coach 60 tests at Laingsburg), the speed,
brake application, also the train’s location vs gradient and curvature along the
line. We had a portable (Battery operated) 12 channel recorder suitable for strain
gauges, so we used a coupling hook and cemented a strain gauge tension bridge on
a grove cut in it, calibrating it in a tensile testing machine. This took care of the
drawbar force from whatever locomotive would be used (Also for the future
diesel)(Fig 58). Speed was indirectly measured with a coil around a magnet,
positioned by clamp on the loco frame so that we obtained an electric pulse from
the coil as the big end passed close to it every revolution of the driving wheel (Fig
58). At the start of the test we measured how far the loco travelled per revolution
so that we could determine the speed of the loco from the recorder chart which
was set to run at a fixed speed. As a check we also recorded a pip every minute
from a clock. On another channel, coded pips were recorded to place when certain
incidents occurred, e.g. engine slipping; stopping for a signal, etc, of which written
notes were kept. Space was a bit of a problem but in the end we three made
ourselves at home on the back of the tender (Fig 58). Our SAR experience at
Laingsburg helped a lot to plan the tests and they went well The biggest task was
that the original record had to be ‘translated’ into a new record with the position
on the line as the longitudinal scale and speed and drawbar pull on a convenient
mph and lb. scale, which took some time. However, the data was satisfactory for
PPC to draw up the diesel specification. When the diesel arrived (I had already
left the CSIR by then) it went through the same test procedure as before and was
found satisfactory.
One interesting result was that the initial force to start the train on a level track
was far greater than normally accepted for trains. For the 3’ 6” gauge trucks of
those days, a value of 4½ lb/ton is normally found; in these tests, the value was 8
lb/ton for loaded trucks and as high as 15 - 20 lb/ton for empty trucks. One can
only surmise that the alignment of the bogies and the track was not up to the SAR
norms for the 3’ 6” track.
As mentioned above, these tests were the last I could manage as far as Railways
and locomotives were concerned; thereafter I was so fully tied up with the Atomic
Energy Board and UCOR that I never got involved with trains again, except for
56
one or two trips by Friends of the Rail and the like, and one very Grand Finale, the
inaugural trip in 1972 of the (then) new Blue Train (As designed by brother Kobus
with some input no doubt from his wife Rita) to Kimberly and back - a wonderful
experience to remind one why locomotives are needed, even though no steam
locomotives are involved!
Appendix A
Locomotive and Tender Numbering Systems
Each steam locomotive has three numbers: The Class, the Individual and the
Maker’s Number. The first two are prominently displayed on the oval red Number
Plate, one on each side of the cab (just visible in Fig 4 & 11 top). The individual
number is the large central number; the small one under it is the class. Well below
the Number Plate is a small plate with the maker’s name, his serial number and the
date of manufacture.
Individual numbers are unique per locomotive; the individual number is the loco’s
name: a number such as 3211 is spoken as thirty two - eleven, and never as ‘three
two one one’ On ordering a new batch of the same type of locomotives, a block of
new individual numbers and the class number were allocated, eg the first batch of
locos with 5’- 3” diameter wheels was allocated the Class 23, Numbers 2552-2571,
and the repeat order 3201-3316, retaining the Cls 23. The tender’s type number
consists of two letters eg EW for the class 23 tender, and they have the same
individual number as the loco.
Class Numbers reflect further information, eg: 19. A number without letters means
that it is the first batch of a new type of rigid frame steam locomotive, or a further
batch of the same type (Fig 1).
19A. Indicates a batch of loco’s basically the same as the cls 19, but with a few
changes, in this case the wheel diameter was changed from 4’-6” d into 4’-3” to
reduce weight for lighter branch line work.
15AR. A 15A loco reboilered with (in this case) a standard No 2 boiler.
S, S1, S2 Shunting locos. (No bogie wheels) (eg Fig 3)
G. Garratt locomotives, ie a central boiler pivoted onto two engines (Fig 9).
GM. The 13th Garratt class
GMA. The same as the GM (suitable for 60 lb/yrd track), but with, in this case, cast
steel frames instead of bar frames.
GMAM. The GMA with increased water and coal capacity, for main line working
(Fig 9).
57
MA, MB - MJ1 Mallet locomotives (eg Fig 12). Not to be confused with the
previously mentioned ‘M’.
Other Types of Locomotives eg:
• 7E2. The seventh type of Electric Unit, second variation.
• 34-214. Class and individual numbers combined: Diesel loco No 214 of class
34. Diesel loco classes start with 30.
• NGG 16. Narrow gauge Garratt locomotive, class 16. The last of the line.
Let us not get involved in pre-Union, harbour, experimental, etc,etc---
Appendix B
Eleven Representative SAR Locomotives
These notes introduce 11 locomotives which were chosen as relevant to the later
more detailed discussions as to what made the steam locomotives work well -or
not so well.
19 and 19d (Figs 1 & 2) The class 19 was the first SAR locomotive designed by
my father “MM”. It was in response to an unusual request by the Chief
Mechanical Engineer, Col Collins, in 1926 when “MM” had only been one year in
the service - it was the CME’s prerogative to design new locomotives himself. The
cls 19 was to replace ageing loco’s (eg cls 6,7,8 ) for branch line working on 60
lb/yrd track. It was a brilliant design that proved so effective that the basics were
retained for 23 years, when the last order for 19D’s was placed. “MM” was CME
then and introduced the larger ‘Vanderbilt’ torpedo shaped tender (“Die Perdeby
kolewa”) on 6-wheeled cast steel ‘Buckeye’ bogies, and vacuum brakes on the
engine. It proved reliable, effective and powerful; it is still the preferred loco by
Rovos Rail and on the George - Knysna line. A large (by branch line standards)
fire grate (36 sq ft) combined with big cylinders and long travel cylinder valves
worked wonders. Note also the change in cab design: the cab floor is higher and
extended towards the tender - there is no floor attached to the tender any more.
The fireman now has one stable footbase from which he can do his stoking. Total
number of engines ordered was 336 (19-19D).
S1 Shunter (Fig 3) “MM”s wartime design to suit local manufacture. Simple but
powerful. Only low speeds are involved so that small driving wheels could be
used, reducing the weight to the point where bogies could be eliminated. The
adhesive weight was the same as for a main line locomotive such as the 15F, which
meant that the S1 could on its own easily without slipping “lift” and shunt a train
58
dropped in the yard by the 15F. There was weight to spare so that a large standard
boiler (Cls 12AR) could and was fitted.
24 (Fig 4) “MM”s last design. Intended for very light (40¼ and 45 lb/yrd) branch
line work, particularly in the then SWA. It was the first SAR loco to use a light but
strong cast steel frame integral with the two cylinders, boiler saddle and supports
(Fig 41) dealt with in section 7. The lighter frame enabled a shortened version of
the 19D boiler to be fitted - extremely powerful for such a “small” locomotive.
This called for a larger than normal bogie under the firebox. Raimund
participated in the first trip of the Cls 24 with an ore train through the Kruger Park
from Palaborwa to Komatipoort on the now defunct “Selati” line. Quite an
experience to sit on the front cowcatcher at dawn and see a family of cheetahs
scrambling off the track as the driver blows the whistle! 100 locos were ordered
but they had a limited life as all the light branch lines were upgraded soon
afterwards. As far as I know, no problems were experienced with the 2-8-4 wheel
arrangement - after all the loco was used at low speeds.
16E (Fig 5) Chief Mechanical Engineer Allen Watson’s proudest design - the
only SAR locomotive with 6’- 0” diameter wheels. Intended for the early “Blue
Train” and other expresses, it reached 72 mph on test with a light load. The
revolving cam (RC) valve gear with poppet valves was good at high speeds, but
strangely enough was found wanting on Watson’s 15E with four coupled wheel
sets, which developed about 10% lower tractive effort when starting a heavy goods
train than its later model, the 15F with Walschaert’s valve gear. This I can confirm
from working the dynamometer recording table during the 1949 traffic tests in the
Karoo.
The new standard 3A boiler of the 16E, with its 62½ sq ft fire grate, could produce
enough steam for a large power output but the cylinders were too small to make
use of it. This can be deduced from the engines low Tractive Effort - see Table B1,
column 7, compared with that of the 15F (18% more) with the same boiler capacity.
The 15F could in any case reach 60mph, the maximum allowable. It sadly led to
the 16E’s relegation to minor duties. The new Blue Train was too heavy! Why
were larger diameter cylinders not used? Read all about it in section 3 on loading
gauge limitations.
15F (Fig 6) (See also 16E above). The standard main line loco 1938-1955 -
altogether 254 ordered. As mentioned above, it proved suitable for both goods
and express service on the main line. However, the 3B boiler with its large square
grate, the rounded ‘Wooten” water space design and the long fire tubes led to high
maintenance costs. It was also prone to “pulling the fire”. These will be dealt with
in section 5 on Boilers. Mechanical stokers were fitted as soon as these became
available - grates over 60 sq ft in size require too much stoker effort for hand
firing.
59
23 (Fig 7) this was CME Day’s proposal to improve still further on the 15E/F. Day
wanted an improved larger boiler and 5’-6” driving wheels, but this would have
taken too long to design, and WW2 was on its way. He had to compromise by
using the standard 3B boiler of the 15F and wheel sizes limited to 5’-3” diameter.
Even they proved to be too large, the longer frame causing increased transverse
flange forces on curves. The higher boiler pressure with corresponding increased
cylinder loads also led to higher stresses in the frames. Fatigue cracks developed
soon in the frames near the cylinders. Repair by welding was ineffective-
withdrawn about 1970.
The boiler had the same problems as that on the 15F. When the tests on the 3B
boiler were planned in preparation of the design of a better boiler for the cls 25,
the best section was from Laingsburg, a water station, to Pietermeintjies. The
steady climb was long enough to get reliable test results. As this was the ‘home’ of
the Cls 23, one of them, No 3211, was chosen for the tests in 1949.
On the plus side of the Cls 23 was the bigger tender which made travelling
through the dry Karoo much better, but there again the design of the six-wheeled
bogies with their bolted construction proved too light: the forks guiding the axle
boxes permanently deformed outwards, placing excessive end loads on the SKF
self-aligning roller bearings (Fig 8). This led to their early failure at the end of the
WW2, when no spares were obtainable. Brother Kobus saved the situation by
rapidly setting up production facilities to make replacement “Isothermos” axle
boxes in the SAR Workshops. (Raimund had been told to check what was causing
the problem. He joined the breakdown gang at midnight in the middle of a
snowstorm at Pietermeintjies (the coldest part of the main line), where a failure
had occurred. The gang lifted the failed tender, leaving me to crawl under it with
my tape measure to check dimensions, before their actions led to further
deformations. They withdrew quietly to their fire so as not to be disturbed by my
chattering teeth. Anyway, the surmise proved correct and the Loco Drawing
Office (LDO) got cracking on designing stiffeners for the bogies).
GMAM (Fig 9)(Die Gammat). The most modern (1954) and most successful of the
SAR Garratts. Basically the same as the pre-war GM, ie of the same wheel,
cylinder and boiler size, but modernised with cast steel frames integral with
cylinders, vacuum brakes on the driving wheels, mechanical lubricators and roller
bearing axle boxes. It is the same as the GMA, allocated to branch lines with 60
lb/yrd track, but with increased water and coal capacity, for main line working
(hence the extra ‘M’). A total of 150 were ordered. Like the GM, an auxiliary water
tank was trailed by them. The advantage was better adhesion and longer trips
before watering. They still suffered from coal shortages due to a limited coal
capacity of 14 tons, compared to the Cls 23 with 18 tons even with a slightly
smaller fire grate.
Raimund was sent as the Northern Transvaal System’s representative to
participate with the Test Section’s crew (The same as he had joined at Laingsburg)
in commissioning the first GMAM, No 4051, including the trip from Waterval
60
Onder to “Boven”. The load was the same as handled by a ‘double-header’ 15AR
pair, which is a stiff test. Some months before, a GM was sent to Waterval Boven
for the training of drivers and firemen on the handling of Garratts with mechanical
stokers, two new experiences for them. What went wrong I did not hear, but
before we came a local crew had to cope with a stalled GM (low boiler pressure?)
in the tunnel between “Onder” and “Boven” while hauling a load up the gradient.
Both driver and fireman died on the spot due to asphyxiation. It was against this
background that we started with our full load from Waterval Onder. The GMAM
had steamed well so I requested the chief to allow me to join them in the cab on
the trip. We made a good start but I soon found it advisable to climb into the coal
bunker and trim the last bit of coal into the mechanical stoker’s conveyer screw,
otherwise who knows? Garratts never have enough coal! She had incidentally
been running up the bank at 19 mph, with the regulator fully open, at full boiler
pressure and the cut-off set at 60%, a remarkable achievement. On arrival at
Boven, we found that the piston rods looked overheated and had turned blue, in
spite of adequate mechanical lubrication. Working her too hard or are there too
many superheater elements? I never heard the full story as I left the SAR shortly
after.
25(condenser) and 25NC (Fig 10) . The last and the largest non-articulated steam
locomotives on the SAR. The engine part with the driving wheels, cylinders and
valve gear were the same basic size as on the 15F, but Timken roller bearings were
used on all axles, shafts and even on all rods. Mechanical lubricators took care of
all moving parts including the valves and pistons. A massive cast steel frame
integral with the cylinders was supplied by the General Steel Castings Corp from
the USA. They also provided the cast steel frames for all loco and tender bogies.
A larger boiler was designed, based on the Laingsburg boiler tests of 1949/50 (See
section 5). The extra weight meant that a 4-wheeled back bogie had to be used.
The 25NC performed exceptionally well, a ‘clamp-down’ became necessary to stop
drivers from regularly running up to 70 mph on the Karoo main line. The
condensers worked reasonably well but the maintenance was high. They were all
converted to non-condensers in due course.
26 (Fig 11). In 1981 a last attempt to increase the efficiency and power of the
25NC was made under the supervision of David Wardale. Loco 3450 was rebuilt to
include many features, as quoted in the literature (Refs 11, 12 & 15). Raimund has
no direct information on the cls 26 other than a TV shot showing her slipping
badly on starting with a load - in spite of an improved sanding gear. The
improvements included:
• Converting the boiler to Porta’s gas-producer combustion, increasing the
number of superheater elements and damping the flow through the other tubes
at low power levels. The details are dealt with in section 5, Boilers.
• Increasing the boiler pressure. No specific value has been quoted, but 240 lb/sq
in is a good guess.
• Lengthening the smokebox and introducing a double chimney Lempor exhaust.
(Double chimney exhausts had already been used before on some of the 25’s).
61
• Adding a feed water heater between the two chimneys, heated by the exhaust
steam
• Increased steam chest size plus valve gear improvements to cope with
lubrication at the higher temperature
• Fitting compressed air sanding gear
• Increasing the tender coal capacity by 2 tons
It was claimed that the coal consumption was reduced by 35%, the water by 20%
and the maximum power was increased by 50%. Apparently the maintenance staff
had problems in handling so many new types of equipment so that some were
abandoned in due course. The feed water heater and its pump were amongst
these.
In the end, the improvements were not sufficient to warrant further conversions.
Why not? The 26 could not comfortably ‘lift’ a significantly bigger load than the
25, as the adhesive weight had remained substantially the same. The extra power
would give an increased speed, but that was not the basic limitation of the 25. The
25 could already run the Trans Karoo at speeds up to 50 mph up the bank from the
Orange River and well over the 60 mph limit for the Blue Train elsewhere. The
good improvement in economy was welcome, but the potential savings for the
limited life still left for the steam locomotive would, I think, not cover the cost of
the conversion. If not satisfied with this opinion, try to struggle through The Final
Verdict
The Final Verdict: No verdict without sufficient evidence, in the case of Steam
vs Electric/Diesel! To assist in this Case, the most relevant data of the eleven
steam locomotive types mentioned above have been given in the Table B1, together
with those of a contemporary Electric and two Diesel locomotives. A further Table
B2 was prepared from Table B1 in which the data were used to calculate and
compare the maximum load of a train that could just be ‘lifted’ up an incline of 1in
100, such as is found on the Kimberly - De Aar main line, and the maximum
horsepower available to handle a train of 3000 tons up this gradient. In both these
cases allowances have been made for the weight of the locomotives, which absorb
a pro rata amount of the available tractive effort as well as horsepower. The
comparisons have been made on the basis of double header Cls25 and 26 locos
versus double and triple headers Cls 6E1 units as well as Cls 34 diesels, as the
handling of heavy loads is a priority.
There are problems in comparing with the Cls 26, as no reliable data comparable
with those of the other locos were available to me. Reasonable assumptions were
that the loco total weight as well as the weight on the driving wheels had
remained the same as the 25NC. The changes could hardly have influenced them
by more than about 1%.
The tender weight was increased by 2 tons to allow for the extra coal capacity. The
tractive effort was increased by 240÷225 to allow for the higher boiler pressure
(factors such as wheel and cylinder sizes were not changed). The Horsepower
62
increase is debateable: Ref 15 quotes “-dynamometer --on some of these tests more
than 4000 hp was achieved--”, which appears well founded. Ref 12 is general and
appears to quote a more optimistic press release stating “Compared to the Class
25NC, the Class 26 has 35% reduced coal consumption, 27% reduced water
consumption and 50% increase in maximum drawbar horsepower.” The ‘drawbar
horsepower’ is derived from indicator horsepower and only has meaning if the
train load is given. Furthermore, are the other savings cumulative values over a
long period with different load conditions, or the best values for a particular
condition? On what values for the Cls 25 are they based? The following approach
is suggested for reasonable comparisons.
As mentioned above, the power is best expressed as the Indicator (or Cylinder or
Tractive Wheels) horsepower, which is an independent power value from which
drawbar (ie Load) horsepower can be simply calculated, as was done in Table B2.
Also, what was the comparative horsepower value for the Cls 25 - I have not seen
it published anywhere? The approach followed is the following:-
From Ref 1, a good prediction of the power expected from the Cls 25 was obtained
from a reliable source: the leader of the Laingsburg Cls 23 boiler tests. Raimund
confirms from his participation in these tests that the Cls 23 reached a 3000
maximum cylinder horsepower under passenger train running conditions. The
class 25 has a 12% bigger fire grate area, and some further boiler improvements
such as the higher boiler pressure would increase the output by a further factor of
about 1,04. This leads to a reasonable maximum cylinder power output of 3500 hp
for the 25NC. Assuming that the maximum drawbar horsepower for the Cls 26 was
achieved with the same train load as for the Cls 25, then the increase percentage
would also apply to cylinder horsepower. Applying the quoted increase of 50%
leads to 5250 cylinder hp for the Cls 26. This cannot be reconciled with the value
of “more than 4000 hp” from Smith and Bourne. Also, a “35% reduced coal
consumption” would imply a boiler efficiency approaching 80%, which is hard to
accept even with improved burning, as the temperature of the superheated steam
was increased: the smoke outlet temperature would also increase leading to some
reduction in boiler efficiency. As a compromise, a value of 4500 cylinder hp for the
Cls 26 was used in Table B2, a figure which is probably still on the high side.
In Table B2, values for Locomotive Weight (which include tender or auxiliary
water tank) and Maximum Sustained Horsepower (a term vital for comparison
with the Electric Locos) were taken from Table B1 and multiplied by the number of
locos. The available Tractive Force to start the whole train with locos was taken as
the Tractive Effort times the number of locos, except for Cls 26, where this value
was reduced slightly to correspond to a friction value of 28%, already a
dangerously high value.
The “Load Lifted on 1 in 100 gradient” is calculated on the basis that the gradient
effect amounts to 20 lb/ton, and total friction and other losses to 5 lb/ton, a total of
25 lb/ton. The netto load in tons, which can be lifted, is then derived by dividing
63
the Tractive Force by the 25 lb/ton, and subtracting the weight of the locomotives.
A reasonable way in assessing how effective the horsepower values are, was to
calculate in the same way what the available drawbar horsepower would be if the
locos were hauling a 3000 ton load.
The Verdict is then that three Cls 6E1 Units or Cls 34 Diesels would have to be
used to have the same horsepower available under typical passenger train
conditions (assuming the optimistic power value for the cls 26 holds), but that the
load that they could then lift would be 1,7 resp 2,1 times as much. Even then, the
two Cls 26 locos would need double the number of footplate staff. This analysis
does not take factors detrimental to the steam loco such as delays to take on
water/coal and maintenance costs into consideration, or the factor of fuel or capital
cost. Case dismissed.
But - what about the other alternatives for BIG steam locomotives? Why not
articulated locos like the Mallets? Yes, if we look at Fig 12, we find that the
world’s biggest steam locomotive was indeed a Mallet. The Mallet articulated
design calls for splitting the engine part into two halves, each with its own
cylinders, valve gear, etc. The front half pivots around the rest, and also supports
half the total loco weight, so that it can adequately contribute to the total power
output. Boiler size remains a limitation, particularly if the loco has to be able to
negotiate sharp curves - the boiler front will project outwards só far that it needs
to be tapered. It does not, however, have the limitations of the Garrett loco which
has to carry all its coal and some of the water on the engine part. The ‘Big Boy’
had at least 50% more tractive effort than a Cls 25 double header, but only the
same horsepower. It would not have been suitable for sharp curves. Our
experience with Mallets was poor on the whole: double expansion
(‘Compounding’) was used, but only the last orders had superheaters (See the MJ,
Fig 12) and even the later models had troubles, one being broken boiler tubes as
the boiler was too long. Somehow the SAR abandoned the design in the twenties.
I have no further information but that the ‘Big Boy’ did not save even the
American steam locos.
Now take a breather before we carry on with the details of what made the locos
work - or not.
B7
Table B1 - Locomotive Power Data
S
t
e
a
m
Cl
Loco
Year
T
r
a
c
k
lb/
yrd
Max.
Axle
Load
ton-
cwt
Drivi
ng
Wheel
Sets
- Dia
Cyl
inder
Num
ber
Bore
” x
Strok
e”
Trac
tive
Effort
lb f
Driv
ing
Wheels
total
Axle
load
t-c/lb f
Fric
tion
Fac
tor
%
B
o
i
l
e
r
Press
ure
lb/sq
Grate
Area
sq ft
Esti-
mate
d
Max.
Hp.
Total
Mass
short
tons
64
in
24 1948 40¼ 11-10 4 -
51”
2 -
19”x
26”
27 600 45 - 4
101280
27% 200 36 1800 145
19D 1949 60 13 -
19
4 -
54”
2 -
24”x
26”
31 850 55 - 7
124 040
26% 200 36 1800 171
GO 1954 45 13 - 8 8 -
54”
4 -
18½”
x26”
49 430 106 - 16
239 360
21%*
*
200 56,6 2700 237*
Mai
n
Line
S1 1947 96 19 -
18
4 -
48”
2 -
23¼x
25
38 000 74 - 8
166 660
23% 180 42 2000 157
16E 1935 96 20 -
19
3 -
72”
2 -
24”x
28”
35 820 59 - 14
133 730
27% 210 62½ 2800 187
15F 1938 96 18 -
15
4 -
60”
2 -
24”x
28”
42 340 74 - 10
166 880
25% 210 62½ 3000 205
23 1938 96 18 -
14
4 -
63”
2 -
24”x
28”
43 200 72 - 10
162 400
27% 225 62½ 3000 241
25N
C
1955 96 19 - 6 4 -
60”
2 -
24”x
28”
45 360 74 - 5
166 320
27% 225 70 3500 250
26 1981 96 19 - 6 4 -
60”
2 -
24”x
28”
48 380* 74 - 5*
166 320
29%* 240* 70 4000(
15)
5250(
12)
252
GM
AM
1954 81 15 -
14
8 -
54”
4 -
20½”
x26”
60 700 122 - 3
273 620
22%*
*
200 63,2 3000
+
292*
GL 1929 96 18 -
14
8 -
48”
4 -
22”x
26”
78 650 144 - 17
324 460
24%*
*
200 74½ 3600 236
Elec
tric
Unit
s
6E1 1985 96 21 -
17
4 -
48”
- 49 460 196 030 25% - - 2950 98
Die
sels
35 1972 60 13 -
10
6 -
36”
- 45 190 181 520 25% - - 1430 91
34 1971 96 18 -
10
6 -
40”
- 61 150 248 680 25% - - 2600 111
* Estimated value ** Calculated on the basis of loco/auxilliary tank with full supplies included.
Table B2 - Locomotive Performance Comparisons
Ref Loco
s
Cls x
no
Staff
on
locos
Loco
Mass
ton
F
Tra
ctiv
e
For
ce
F
Load
lifted
on
1/100
Gradie
nt
short
tons
F
Max
sustaine
d
Cyl. Hp
F
Hp.
for
3000 t
Load
F
1 25N 4 500 1 90 <1 3630 - <1 7000 0,8 5810 0,8
65
C x 2 700 500=31
30
2 26 x
2
4 504 1 95
000
1 3800 -
504=33
00
1 9000 1 7470 1
3 6E1
x 2
2 196 2,6 99
000
1,1 3960 -
196=37
60
1,1 5900 0,7 5550 0,74
4 6E1
x 3
2 294 1,7 148
500
1,6 5940 -
294=56
50
1,7 8850 1,0 7970 1,07
5 34 x
2
2 246 2,0 122
300
1,3 4900 -
222=46
80
1,4 5200 0,6 4810 0,64
6 34 x
3
2 369 1,4 183
500
1,9 7340 -
369=69
70
2,1 7800 0,9 6950 0.93
Note: The Factor F is an indication of how much better the other alternatives are
relative to 2 x 26 locos, ie a factor less than 1 shows that alternative is poorer than
the 2 x 26. All tons are short tons of 2000 lb.
An Addendum on Fuel Costs: Fuel costs can be roughly compared between Steam
and Diesel Locomotives as follows:
The Steam Loco is about a quarter as efficient as the Diesel (Overall efficiency
about 6% and 25% resp.)
Compare 1 ton of coal used by the steam loco at a (high) price of R400 with the
diesel equivalent. The heat value of the coal is taken as 14 000 and that of the
diesel fuel as 19 000 BTU/lb. The Diesel will therefore need ¼ x 14/19 x 2000 lb of
diesel oil, or 368 lb = 167 kg of fuel. At a specific gravity of 0.9, this equals 186
litres. The basic price of diesel is about 3 R/litre.6
The Diesel’s fuel cost for the same power output at the driving wheels is therefore R
557/400 or 40% higher than the steam’s.
Fuel costs are not as important as one feels instinctively. The two Cls 25s dealt
with in Table B2 hauling their 3000 ton load up the gradient will reach 30 mph.
The firing rate will be 170 lb/hr per sq ft of grate x 70 sq ft x 2 locos = 12 ton/hr. At
30 mph this amounts to 12/30 or 0,4 tons per mile, a cost of R160 per mile. They
are, however, moving 3000 tons, making it 5,3 cents per ton-mile. How much does
my petrol bill amount to for my car of 1,5 tons doing ten km per litre? At 5 R/litre,
it would be about 30 cents per km, or 50 cents per ton-mile.
Any more questions?
6 'Fuel cost values are those applicable in 2005'.
66
Appendix 1
Summary of Robin Barker’s View of the Origin of the 4’-8½” Rail Gauge
Robin Barker gave Raimund a three-page paper at the last U3A session on “Our
Steam Locomotives”. The title is BRITAIN’S (not so) PECULIAR RAIL GAUGE
(© Copyright: Robin Barker, Pretoria 2003).
It is based on references JB Snell: Early Railways, & OS Nock: Encyclopedia of
Railways and after consultations with Philip Brooks of Wylam Historical Society,
Andy Guy of Beamish Open Air Museum and Philip Atkins of the National
Railway Museum, he sorted out some conflicting information on how ‘wheel’ and
‘rail’ gauges had been quoted in the period before and up to the time inner wheel
flanges became the standard. He puts forward a strong case that the development
started from 18thC horse-drawn coal carts that ran (more or less) on the stone block
strips. It seems that these wheels were conveniently spaced 5’ apart as measured
from outside to outside.
When cast iron became available at the turn of that century, the collieries started
using plateways of cast iron. Robin puts forward a case that they were L-shaped
strips and that they were screwed onto the stone blocks with their vertical flanges
on the outside- this gave the ponies more room to move. The cast iron strips were
brittle and were very short-lived.
When malleable iron became available, the Wylam Colliery 5-foot outside flanged
plateway was rebuilt by engineer William Hedley, probably by bolting thick
malleable iron strips in a vertical position to create what became known as an Edge
Railway.
The edge had no flange; instead the wheels were given outside flanges he thinks.
This railway misleadingly retained the five-foot gauge designation. (Note by
Raimund: I am speculating that the initial conversion of the wheels could have
been done by merely clamping a disc of about two inches greater diameter to the
outside of the wheel - the wheel position on the axle could have been left
unchanged. Naturally, the wheels would soon have been changed for solid
flanged tyres when the better shape proved necessary)
Robin came to the conclusion that the distance between the iron plates remained
the same (see sketch), regardless of what the track gauge was now called. As the
disadvantages of outside flanges became clear (Wheels are more easily dislodged
and bumped off the axle with outside wheel flanges as is also the case with inside rail
flanges), the Wylam Colliery railway was converted in 1862 to inside wheel flanges,
leaving the track basically as it was. This meant that the gauge of the track as
measured from inside edge to inside edge became 4’-8”, soon to be adjusted to 4’-
67
8½” for added clearance. This accorded with Stephenson’s design and was
retained as the British and American main line gauge.
In short, the point made is that the 4’-8½” rail gauge was a logical consequence of
starting off with a nice round figure of 5’-0” spacing (outside to outside) of the
flangeless wheels of their precursors running on stone block strips.
Figures
FIG 1 & 2
68
69
FIG 3 & 4
70
FIG 5 & 6
71
FIG 7 & 8
72
FIG 9
73
FIG 10 – Class 25 & 25NC (1953 – 1955)
Fig 11
74
75
Fig 12 Local & USA Mallets
76
Fig 13
Fig 14
77
Fig 15 & 16
78
Fig 17
Fig 18
79
Fig 19
Fig 20
80
Fig 21
Fig 22
81
Fig 23
Fig 24 Cab of GMAM 4051
82
83
Fig 25
84
Fig 26
Fig 27
85
Fig 28
Fig 29
86
Fig 30
87
Fig 31
88
Fig 32
Fig 33 Loss of White Metal after Overheating
89
Fig 34 & 35
90
Fig 36 & 37
91
Fig 38 – Model of a Walschaert Valve Gear
Fig 38 - Settings
92
Fig 39
93
Fig 40 & 41
94
Fig 42
95
Fig 43
96
Fig 44
97
Fig 45: Class 25 Overlubricated
Fig 46
98
Fig 47
Fig 48
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Fig 49
Fig 50
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Fig 51
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Fig 52
Fig 53
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Fig 54
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Fig 55
Fig 56a
Fig 56b
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Fig 57
Fig 58
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Steamloco Images
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Photographs7
7 Some are better than those in the text – these are from the slides that accompany the
“talk” when delivering the paper.
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And that’s all Folks! I sincerely hope you enjoyed this special edition. On a personal
level I learnt a lot! Our special thanks to Dr Loubser and Mr Les Pivnic.
Kind regards,
Hennie Heymans
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