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KN ACKNOWLEDGMENT .
The authors desire t o express their
grat itude t o Professor !oseph B. Finnegan
and Er . Hamilt on Allport , whose effort s and
co-operat ion make this report possible .
we also are indebt ed t o the staff
of the Underwrit ers ' Laborat or ies for helpful
sugge st ions made in this thesis and for the
use of Laborat ory equipment .
Kenneth V. Hall Frank !. Conway.
May 51 , 1917 .
Combust ion Retarding Apparatus .
TABLE OF CONTENTS .
Obaeot
Table of Cont ent s
List of Illust rat ions
Part 1
Int roduct ion
St at ement of Trade Cust oms
Part 2
General Survey of the Sub!ect
Methods of Using Screens
Part 3
Design and Const ruct ion of Apparatus
Cal ibrat ion of Apparatus
Part 4
Descr ipt ion of Test s
Re sult s
Curves
Part 5
Rest at ement of Problem
Discussion of Var iable Fact ors
14
16
65
66
Combust ion Retarding Apparatus .
LI ST OF ILLUSTRATIONS .
Figure
1- Fill and Vent Fit t ing
Combust ion, &pparatus
5- Observat ion Port s
End'
Flang es
Asp irat or
5- Relief valve
5- Spark Plug
6- Wiring Diagram.
7- Valve Layout
8- Screens
Introduct ion,and Stat ement
of Trade Cust oms in the Han_
ufacture of Wire Screens .
Combust ion Retarding Apparatus .
INTRODUCTION.
The first person t o employ the
known phenomenon,that combust ion will not
pass thru the mesh of f ine wire screens,was
Si r Humphry Davy. The Davy lamp consist sg es-
sent ially of a wire screen cylinder surrounding
the flame of an ordinary miners lamp . The gas
passes thru. the meshes t o supply the flame but
the flame does not flash out thru the meshes
when in the presence of explo sive mixtures of
gas and air . The presence of this mixture is
det ect ed by the sputt er ing of the lamp. Cl ose
observat ion will show t iny flames !ust inside
the screen which die out before passing thru the
mesh . The cooling propert ies of the wire screen
cool the flame below the kindl ing point and hence
the flame dies. The l imi t ing size of the Openings
and the size of wire have not been det ermined.
The mere stat ement of the mesh of a wire
screen will not ident ify it . There are certain
Combust ion Retarding Apparatus .
cust oms observed in this industry which we
will quot e from. the catalogue of the F.P.Smith
Wire Iron Works , Chicago , Illinois.
Combust ion Retarding Apparatus .
Terms and Cust oms of the Wire Cloth Indust ry.
Fill ing tarp wires are those which
run longitudinally in the cloth . Filling
wires run t ransversely in the cloth and cross
alt ernat ely over and under the warp wires . In
descr ibing cloth the warp mesh and wire precede ,
in their respect ive posit ions , the same element s
of the f illing . Thus 9 x 8 mosh'
No . wire
indicat es that the warp has 9 meshes per lineal
inch and is made from. No . 18 wire! and the f ill-
ing has 8 meshes per l ineal inch and. is made from
‘No. 19 wire .
The size of any mesh in wire
cloth is the distance from the cent er t o cent er
of it s parallel wires— not the clear space be—
tween these wires . The numeral which precedes
this word in the descr ipt ion of the cl oth in!
dicat es the number of Openings it has in one
lineal inch . Thus 4 mesh means that the cfloth
has 4 openings per lineal inch , each measur ing
Combust ion Retarding Apparatus .
from cent er t o cent er of it s parallel
wires.
The clear space between the wires is
det ermined by the size of the wire used in. the
cloth and is found by deduct ing the diamet er
of one of it s wires from. the size of the mesh .
Thus , if Hb .16 st eel wire !which is
diamet er! were woven int o 4 mesh cloth , it
would show inch clear space , or inch
!size of mesh! less inch !diamet er of
wire!.
The f illing meshes in many of the
very f ine grades,and also in some of the medium
ones made from. the largest wire that can be woven
in each,are somewhat larger than the warp meshes
because it is impossible t o force wire beyond a
certain point without straining it and impairing
it s eff ic iency.
Space This t erm, or as it is some-
t imes expressed "hole ' or 'Opening ", means clear
10
Combust ion Retarding Apparatus .
t o which they are subg ected in the loom t ends
t o elongat e them and slight ly reduce their
diamet ers.
The Wire-Cloth flanufacturers ' Asso-
ciat ion adopt ed the old English Gauge as the
Standard for all brass or copper wire cloth.
No . ofGaug e
20
21
22
23
24
25
27
28
29
30
31
32
33
35
36
OldEnglish
.035
.0315
.029
.027
.025
.023
.0205
.0188
.0165
.0155
.0138
.0123
.0113
.0103
.0095
.009
.0075
U.S.
.0375
.0344
.0313
.0281
.0250
.0219
.0188
.0172
01410125
0109
01020094
0086
0078
0070
Standard Amer ican
03200285
0253
0226
0201
0179
0159
0142
0126
0113
0100
0089
0080
0071
0063
0056
0050
COMPARISON’
OP VARIOUS HETAL GAUGES.
NO 0 0f
12
PART 2 .
A Survey Regarding the
General Principles and Important‘
ractors
Ent ering Int o the Study of Ret ardat ion of
Combust ion Thru l ire Screens in Closed Pipes ,
Together with a Summary of the methods of Using
Wire Screens Today.
13
Combust ion. Retarding Apparatus .
A STATEMENT OF THE PROBLEM .
The widespread use of Gasolene and
it s relat ed product s has built up the demand
for some safe way t o st ore these commodit ies .
It has been thought by invest igat ors that the
plac ing of a wire screen or a perforated. plat e
in the vent pipe would prevent the passage of
combust ion int o this st orage tanks . The
problem. then resolves it self around the law
of cool ing and radiat ion as applied t o the
screen and pipe it self . The probabilit y of
the combust ion flashing back is influenced by
the ignit ion t emperature of the gas , r ichness
of explosive mixture,calor ific value of the
gas , spec if ic heat of gas and air and the spea
cif ic heat of the product s of combust ion.
It is a well known fact that gases and
vapors in general are not actually explosive
except when mixed with air or oxyg en and then
only When the mixture is in def init e preport ions.
14
Combust ion’ Ret
arding Apparatus
FILL AND VENT FITTING AS USED ON STORAGE TANKS .
The fill pipe for an underground st orage
tank can not be opened without simultaneously
Opening the vent pipe . r111 and Vent openings
are provided with screens . Each f it t ing is
placed direct ly in a flange provided in the
underground st orage tank! the inner or f ill pipe
of the combinat ion fitt ing ext ends below the
out er or vent pipe so that the issuing vapor
will not t rap the incoming l iquid . Details of
construct ion are shown by f igure 1 for the com-
binod f illing and vent ing fitt ing which is used
when the tank is not permanent ly vent ed. If the
tank is permanent ly vent ed with a suitably'
pro—
t oot ed vent p ipe as required in some localit ie s ,
all that is necessary for the f illing pipe is a
properly locked and screened pipe , which is
accompli shed by having a simple two inch vent
provided with a locking and clos ing mechanism as
shown in f igure 1 and equipped with a screen as
16
Combust ion. Retarding A
shown by the same drawing with a wider
flange so that it will hang on the t op of
the out er pipe .
Combust ion Retarding Apparatus.
DESCRIPTION 0! APPARATUS.
The writ ers have endeavored in this
exper iment t o r eproduce condit ions which
would. most likely arise in standard pipe
lines .
The det ails of the apparatus are
shown by f igure 2 and consist s of two com-
bust ion chambers , two lengths of standard
pipe with flanged ends,for screen insert ion ,
two observat ion port s and flanges of spec ial
design , two specially designed and sensit ive
thermo-couples , two end flanges of special
design , containing taps for spark plugs , gas
and air vent s , relief valve,manomet er and
aspirat or connect ions.
The following is a list of the standard
pipe f itt ings used!
8- 4 ' Tees .4- 4 ' Flang e Couplin
gs .
2- Pieces 4 ' pipe 24 long .1- cross .1- 1 ' cross .2- 9 ' blind flanges with 2 ' t op .
2- 2' observat ion port s .
21
Combust ion Retarding Apparatus .
blind flange with taps .blind flange with and 1 " taps .
2 Thermo Couples .3 Millivoltmet er s .
Globe Valves .Pet cock .
adapt ers .l-l ' relief valve .
Globe Valve .
Gat e Valve .1-Aspirat or , 6 ' pipe .Gas Connect ions .Air Connect ions .
Spark Plugs .l-fl ercury nanomet er .1 Pressure Gauge .Samples t est ed.
Combust ion Retarding Apparatus .
!Advanced wi re! and No . 35 copper wire . They
were fused in an elect ric arc . The sensit ive-
ness of the couples was f irst t e st ed by the
applicat ion of flame and a large deflect ion was
obtained on a millivoltmet er . They were then
t e st ed by the blowing of the breath upon the
couple , which produced an apprec iable deflect ion ,
thus assur ing their sensit iveness in det ect ing
combust ion in the clo sed pipe . The couples were
placed in a p ipe with a right angle bend at
out side end. The space not occup ied by the
thermo-couples thru the pipe was f illed with
plast er of paris . The ob!ect of the right angle
bend was t o avoid the blowing out of the plast er
of par is , by the force of the explosion.
The couples were placed two and one-
half f eet from. the fac es of the scr een , thus
_producing . a deflect ion only when they were in
actual contact with a flame , and not producing
a deflect ion by radiat ion of heat thru the sample .
combust ion Retarding Apparatus .
EndFlanges The end flanges were
or iginally two blind flanges . The head
flange was tapped for spark plug and
a tap for connect ions t o gas , compressed
air and manomet er . The rear end flange was
t apped for a spark plug and a 1 * tap for
relief valve , gas and aspirat or . The flanges
were bolt ed on air t ight . These are shown in
f igure 3 .
Insert ingScreens The problem of insert ing
screens was solved by the use of rubber gasket s
on each side of screen. Bolt holes were cut in
the scr een t o correspond t o bolt holes in 9 '
rubber gasket s. Great care was exerc ised in
insert ing screens so that the mesh would not be
dist ort ed. In this manner an air t ight !o int
was easily obtained.
Asp irat or The aspirat or as shown in
f igures 4 and 5 ,consist ed of a 6 ' standp ipe ,
Combust ion. Retarding Apparatus .
were used as a source of ignit ion for the
gaseous mixture . The spec ially designed
spark plug is shown in figure 5 .
ReliefValve The relief valve was used
t o take care of the excess pressure produced
during the combust ion. Drawing of the relief
valve is shown in detail in f igure 5 .
The valve employed was made Of brass.
It consist s Of a conical valve , seat ing int o a
valve Opening , and. held closed by a spring. The
t ension Of the spr ing could be regulat ed by a
knurled plug at the t sp of the valve . The
valve ficrewed int o a l ' standard. pipe tap in
the rear flange .
Manomet er A 24 ' U shaped manomet er was
used. The liquid was mercury. With this mano-
met er , the difference in. level of the two legs,
and by reference t o curve no .5 the desired per—
centage of gas was obta ined , and by referring t o
50
Combust ion. 3etarding Apparatus.
curve no .5 the desired volume Of air could be
expelled by not ing the manomet er reading . It
was also feasible t o a scertain the air t ight—
ness Of the syst em by int roducing a difference
in. pressure between the syst em and the atmos-
phere and Observing how much l ess in pressure
would take place in a given t ime . One leg Of
the manomet er was connect ed t o the apparatus and
the other leg left Open t o the atmosphere . The
difference in reading on the manomet er shows the
difference in pressure Of the combust ion chamber
and atmospheric pressure .
Induct ionCo il in induct ion co il as shown in
figure 6 was connect ed t o a st orage batt ery thru
it s pr imary coil and the secondary t o the spark
plug .
32
Combust ion Retunding Apparatus .
CALIBRATION’
OP APPARATUS.
VO lume The volume of the apparatus
was det ermined by wat er displacement . The
!oint s were paint ed and made t ight , and the
blind flanges bolt ed on the ends . Wat er was
pour ed int o the Observat i on. port with a standard
U.S.Gallon measure and a graduat ed flask . The
apparatus was found t o contain
Gas— air
Mixture Assuming that gas and air are
chemically inert,the following method was used
for det ermining the p ercentage mixture !
Let VI- Velume Of syst em in c .c . below
atmospheric pressure .
P1- Pressure of‘
V below atmospheric .
2- The volume Of air plus gas in
subaect ed t o pressure ,P3 .
Pza
Atmospheric pressure .
vs! vz
avl or volume Of gas in c .c . tobe added t o the syst em.
Combust ion Retarding Apparatus .
Test The apparatus was t est ed
for leakage by f illing with wat er and admit-
t ing compressed air . Where any Of the wat er
leaked out , marks were made , the apparatus
drained , all leaky !o int s were paint ed and
t ight ened. The syst em was f inally t e st ed by
the use Of the manomet er and asp irat or . All
the valves were closed. The asp irat or was
turned on and a difference of level of mercury
was Obtained. The asp irat or was then shut Off
the difference of mercury in the two manomet er
arms remained constant,thus showing that the
syst em was air t ight . This proceedure was
carried out at each insert ion of a new screen.
56
4 .
DESCRIPTION OF TESTS .
58
Combust ion Retarding Apparatus .
DESCRIPTION OF TESTS .
All of the valves connect ed with the
syst em are closed t ight ly at the start . First
Open the exhaust valve leading t o the aspirat or
then Open the gas inlet , shown in f igure 7 ,
allowing the gas t o run for one minut e . This
will clear out any air that may have been in the
gas lines attached t o the syst em. Close the gas
inlet . The aspirat or is now f illed with wat er
from. the cit y main , and all Of the gas that is in
the syst em may be removed by f illing the asp irat or
several t imes . To fac ilitat e the replac ing of
the gas by air , the observat ion. port on the head
end is removed.
The syst em is now ready for the int roduct ion
of an explosive mixture . The Observat ion port is
replaced in it s original posit ion and all valves
closed. The valve t o the manomet er is opened and
the aspirat or allowed t o drain unt il a difference
in reading of in . Hg . is observed , by referring
Combust ion. Retarding Apparatus .
t o curve no .3 shows a mixture of The
aspirat or valve is now clo sed and the Operat or
on the rear end allows gas t o ent er the syst em
unt il the pressure difference is r educed t o
in . Hg . Then the operat or on the head
end admit s gas int o the combust ion chamber unt il
the manomet er shows no difference in pressure
This indicat es the syst em is under atmospher ic
pressure . All valves are now t ightly closed and
the gas allowed t o diffuse for f ive minut es.
The gas at the head end i s ignit ed by
means Of the spark plug . The combust ion may be
not iced thru the observat ion port and also be de-
t ermined by the galvanomet er deflect ion.
If the combust ion. pasees thru the scr een ,
the galvanomet er on the rear end will show a de-
flect ion and the combust ion. may be seen thru the
observat ion‘
port .
If the combust ion does not pass thru
the sample , the spark is applied on the rear end ,
40
Combust i on Retarding Apparatus .
as shown in f igure No .7 , and the com—-
bust ion can be observed thru the port hole
and the presence of flame also indicat ed by
a deflect ion of the galvanomet er .
If we secure no combust ion on this
second t rial , then it is readily known that
there was not an explosive mixture in that
port ion of the p ipe . Whenever this occurs
another t est should be made using the same
p ercentage mixture.
Aft er the combust ion , the manomet er
valve is Opened and a reading taken of the
decreased volume by reference t o curve No .4 ,
this amount may be ascertained. This reading
will show if complet e combust ion t ook place .
It s reading should always be great er than the
amount of gas put int o the syst em as a per-
centage of the oxygen in the air is consumed
during combust i on.
41
Combust ion Retarding Apparatus .
The manomet er yalve is now closed,
the pet cock on the spark plug Opened , the
aspirat or and compressed air valves Opened.
The aspirat or should be filled and drained
three or four t ime s t o insure the complet e
removal of all burned and unburned gases .
If the sample proves effect ive in
retarding combust ion a richer mixture is
int roduced int o the system. and the sample
t est ed as above .
When the screen fails t o retard at
a certain percentage mixture , a t est using
this same mixture is repeat ed t o make
reasonably sure at what mixture the screen
has failed. Then a new sample i s installed
and the process repeat ed as above .
By finding at what percentage mixture
the different samples prove ineff ect ive and
compar ing these values with those found for
the other screens and plat es , a relat ivit y
FIG . 8 AFTER TEST .
Combust ion. Retarding Apparatus .
The following samples were t e st ed ,
a. p icture of these i s shown in f igure 9 ,
with their respect ive numbers !
Screen No . Mesh
l 20 50
2 16
5 20 50
4 50 57
5 4 ” German Silver Corrugat ed Coil
6 6O 56 Copper
7 40 55 Brass
8 60 56
9 24 55 Copper
45
Mat er ial
Cu .Plat e
Brass
Combust ion Retarding Apparatus .
DATA .
Volume of Syst em 6 gallons pint s .
x
1 gallon 251 cu .i n.
1 pint cu .in .
6 x 251 cu .in
09 cu .in 0
Volume cu .in.
1 cu . ih .— 5 0 0 0 0
x c .c . volume of syst em.
Gas
7
8
9
10
11
12
15
14
15
16
17
x Volume
.07
.08
.09
.10
.11
.18
.15
.14
.15
.16
.17 N
fl
N
H
H
H
M
H
N
N
N
a
46
Gas , c .c .
1720
1955
2200
2445
2685
2950
5180
5420
5660
59104150
Air ,
Combust ion Retarding Apparatus .
DATA .
Lo ssGas x P
3sq.in .
7 .07 x
8 .08 x
9 .09 x
10 .10 x u
11 .11 x
.12 x
15 .15 x w
14 .14 x
15 .15 x
16 .16 x
17 .17 x
in .Hg .
1% sq.in
x
48
Manomet erIn .Hg .
sq.
in .Hg .
2 0 1 in .Hg .
P1In .Hg .
Combust ion Retarding Apparatus .
DATA .
TEST OF SCREEN #6- FIGURE 9 .
60 fl esh #56 Gaug e Copper Wire Screen.
GasMixture
Observed Combust ion .
Head End
Yes
SCREEN #8- FIGURE 9 .
Rear and
NO
Yes
60 Mesh #56 Gauge Brass Wire .
Yes Yes
when Combust ion appears at both head
rear ends , it means the sample proved ineffect ive .
P
T5.Hg .
Combust ion Retarding Apparatus .
DATA .
TEST OF SCREEN #5- FIGURE 9 .20 Mesh #50 Gauge Brass Tire Screens .
When Combust ion appears at both head and rear
2 Gas Observed Combust ion .
hixture Head Ind Rear End .
Yes No
Yes
SCREEN FIGURE 916 Mesh #28 Gauge Brass Wire .
Yes No
Yes
ends it means the sample proved ineffect ive.
58
Combust ion Retarding Apparatus .
DATA.
TEST OF SAMPLE #5- FIGURE 9 .
German Silver Corrugat ed Co il .
P1 Gas Observed Combust ion .In . Hg . Mixture Head End Rear End .
Yes Yes
This coil failed t o retard combust ion
at the lowest percentage mixture obtainable .
This may have been due t o the fact that it was
diff icult t o secure a t ight f itt ing of the co il
int o the p ipe wall.
60
5
A RESTATEMENT OF
PROBLEM AND .A DI SCUSSION
LE EACTORS.
Combust ion Retarding Apparatus .
air , the flame from the spark produces
ignit ion at the point of contact, i .s .
incit es chemical react ion . This combust ion
proceeds t owards the c ent er of the apparatus
and thereby forms a plane of combust ion which
divides the gaseous mixture int o two part s! on
the one side are the highly heat ed product s of
combust ion , and on the other is the st ill una
consumed gas . The dimensions of the two part s
vary in proport ion as combust ion moves from. the
consumed t o the unconsumed. port ion.
The veloc it y at which this plane advances
is different for each gaseous mixture , and de-
pends both on the composit ion Of the mixture and
on the pressure t o which it is sub!ect ed , the
higher the velocity the great er the rise in tame
parature , and this latt er in turn direct ly in—
fluences the expansion of the gas and the pnoduct s
of combust ion,which thereby exert such a st rong
pressure on their environment !air , walls , et c .!
66
Combust ion Retarding Apparatus .
Screen #5- figure 9- a 20 mesh 50
gauge brass wire was second in retarding value,
failing when the percentage mixture reached the
value of
Screen #9- f igure 9 a 24 mesh , 55
gauge copp er wire retarded the combust ion up
t o
Plat e #1- 20 mesh , 50 gauge copper
plat e r etarded the combust ion up t o
Screen #6- 60 mesh , 56 gauge copper
wire failed when the mixture was
Screen #2— 16 mesh , 28 gauge brass
wire retarded the combust ion up t o
Screen #5- 50 mesh , brass wire and
#8 a 60 mesh,brass and the German Silver Cbil
did not retard any combust ion . The flame burned
away that part of screens #4 and #8 which were in
actual contact with the flame .
From. the foregoing result s , it is
indicat ed that the f ineness of the mesh alone will
Combust ion Retarding Apparatus .
mot ion and the sample placed on the down-
st ream. port ion of the Therefore,all
of these samples would hold up much bett er in
actual field work,but the ir relat ive values
as found in these t est s would not be alt ered.
68
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