Devineni Venkata Ramana & Dr. Hima Sekhar

MIC College of TechnologyKANCHIKACHERLA

MINI PROJECT ON SLACK ADJUSTER BARREL [SAB]

BYBHARAT MANDAVA

www.micame.in

ABSTRACT

When brake is applied or released the clearance between brake shoe and wheel thread may increases or decreases. To avoid this slack adjuster barrel is used. Shortly SAB. Our project is about SLACK ADJUSTER BARREL (SAB). It is a device for automatic adjustment of clearance of 5mm between brake blocks and wheel thread. It is a double acting, clearance sensing, axial type and it comprising a barrel which rotate in either direction and Non rotatable Adjuster spindle comprising of pull rod and threaded spindle extending out of the barrel from one of it ends .

Basically, a SAB is divided into 4 sections known as ‘units’. They are Barrel Unit, Traction Unit, Leader Nut Unit and Adjustable Spindle Unit. Here we discuss about the dismantling and reassembly of each unit briefly. Several tests and inspections are followed to ensure the quality of the product. Testing is done to check the proper working of a SAB. The ‘A’ dimension and ‘E’ dimension plays an important role in checking the working of a SAB, hence the procedure for checking is discussed. Other external components like ‘Empty/Load Device’ is also attached to a SAB. Finally safety precautions, working of SAB and trouble-shooting are also included.

Contents

General

Introduction Functions Of SAB Principle Of Operation Components Of SAB

Maintenance

Dismantling Cleaning And Inspection Wear Limits Procedure For Testing Springs Lubrication Reassembling Testing On Rack Testing In Brake Rigging Assembling Of Adjuster Spindle Assembling Of Control Rod Painting

Checking

‘A’ Dimension ‘E’ Dimension Empty/Load Device Adjustment Of Empty Tie Rod Safety Precautions Working Of SAB Trouble Shooting Conclusion References

SLACK ADJUSTER

Slack adjuster (also known as brake regulator DRV-2) is a device provided in the brake rigging for automatic adjustment of clearance/slack between brake blocks and wheel. It is fitted into the brake rigging as a part of mechanical pull rod. The slack adjuster is double acting and rapid working i.e. it quickly adjusts too large or too small clearance to a predetermined value known as ‘A’ dimension. The slack adjuster maintains this `A’ dimension throughout its operation.

The slack adjuster, type IRSA-450 is used in passenger coaches, it is composed of the following parts :

Barrel Unit Traction Unit Leader Nut Unit Adjuster Spindle Unit

BENEFITS OF SLACK ADJUSTER

Fully Automatic : Once initially set, no manual adjustment is further necessary at any time during its operation.

Double-Acting : The brake shoe clearance is adjusted to its correct value both ways, either when it has become too large (owing to wear of the brake shoes and wheels) or when it has become too small (e.g. owing to renewal of ‘worn out brake blocks’).

Rapid working : Correct brake shoe clearance is automatically restored after one or two applications of the brake.

Verification : If resistance occurs early in the brake application, caused by heavy brake rigging, e.g. an ice coating on the brake shoes, etc., in such cases the slack adjuster does not pay out slack immediately, but indexes the amount of slack to be paid out. If the slack really is too small, the slack adjuster will pay out this indexed slack at the next brake application. Thus false payout will not occur.

True Slack Adjuster : The slack adjuster adjusts incorrect slack only, thus giving the brake its best possible pre-adjusted limit of piston strokes, ensuring a smooth and efficient braking force at all times.

Shock Resistant : Train shocks will not cause false take-up or payout of slack. When brakes are released, the moving parts of the slack adjuster are securely locked.

PRINCIPLE OF OPERATION

The position of adjuster nut on adjuster spindle determines the length of the slack adjuster. The leader nut follows the movement of the barrel and its purpose is to lead the adjuster nut to its correct position on the spindle. Control rod is fixed to the brake rigging or the under frame so that when the brake is applied, barrel moves towards the control rod head proportionately to the piston stroke. The distance between the head and the barrel, when the brake is fully released is called the control dimensions 'A'. This corresponds to the correct slack.

If the slack is correct, the control rod head touches the end of the barrel at the moment when the brake blocks start to apply against the wheels and no adjustment will then take place. If the slack is too large, the control nut head pushes on to the barrel increasing the distance between it and the suspension ear by an amount corresponding to the excess of slack before the brake blocks apply. The leader nut follows rotating on adjuster spindle. When the brake is released, the leader nut is, however, locked against the seat of leader nut casing and the barrel spring causes adjuster nut to rotate on the spindle towards the leader nut. This advance of adjuster nut on the spindle

shortens the slack adjuster and adjusts the slack to the correct value.

If the slack is too small the first brake application causes the barrel to screw towards the control rod head until stopped by it. The distance between the two nuts i.e. leader and adjuster has been shortened by an amount corresponding to the deficiency of slack. At the start of the next brake application leader nut is locked in its new position on its adjuster spindle and pay out spring pushes adjuster nut rotating on the spindle until the normal distance between the adjuster and leader nuts has been restored. The slack adjuster is in the way lengthened by proper amount and the slack adjusted to normal.

COMPONENTS OF SLACK ADJUSTER BARREL

Item

Description & Dimension No. Item

Description & Dimension

No.

123456789101112131415161718192021222324

Dust bushing Seal ring Circlip-9.45 x1.75 Rubber gasket Spindle sleeve/Protection Tube Dog pin Bearing 45 TA 11 ( Complete) Leader nut casing Circlip-9.45 x 3 Spring sleeve/Spring Cap Pay-out spring Traction sleeve Guide bushingGuide pinWire ringFriction washerAdjuster tube socketSpring dowel sleeve light – 6 x 10Clutch sleeve Clutch ringSpring Barrel Barrel Adjuster spindleSafety collar

121111111111111112111111

252627282930313233343536373839404142434445464748

Spring dowel sleeve/Roll PinControl rod headLock washerAdjuster earEar bushingCirclip - A 40 X 1.75Leader nut flangeBearing 45 TA 11Lock screwTab washerLeader nutAdjuster nutTake –up spring Actuating sleeveClutch springCirclip - A 45 X 1.75Adjuster tubeBarrel headSeal ringControl rod Multi tooth lock washer B 28Lock nutName plate Rivets

111111121111111111211114

DISMANTLING

The process of disassembling every section from the SAB is known as ‘Dismantling’. It is done in a step-by-step manner. The order followed is :

Dismantling Of Control Rod.

Dismantling Of Adjuster Spindle.

Dismantling Of Traction Unit and Leader Nut Unit From Barrel.

Dismantling Of Traction Unit Assembly.

Dismantling Of Leader Nut Unit Assembly.

Dismantling Of Control Rod

1) Clamp Slack Adjuster barrel lightly, preferably in a pipe vice, close to the barrel head, so as to avoid damage to the barrel.

2) Flatten lock washer. Hold adjuster tube firmly with a pipe wrench and unscrew adjuster ear by rotating anti-clock wise. Remove Control rod together with control rod head.

Dismantling Of Adjuster Spindle

1) Screw adjuster spindle into the slack adjuster until the end with the safety collar protrudes from the adjuster tube.

2) Remove spring dowel sleeve and unscrew safety collar.

3) Then screw adjuster spindle right back out of the slack adjuster.

Note : It is possible that one, two or even three distinct clicks will be heard when the thread of the adjuster spindle leaves the adjuster nut. This is quite in order. Be careful in handling the adjuster, spindle after removal, to avoid damage to the threads. It is advisable to slip a piece of protective cardboard tubing over the threads or to wrap them in thick paper.

Traction Unit and Leader Nut Unit Dismantling From Barrel Unit (On Mechanical Device)

1) Place the slack adjuster on mechanical device and clamp it tightly.

2) Tighten the coupler nut into the adjuster tube.

3) Operate the device wheel so that the device lever is connected to the coupler nut by a pin.

4) Now, operate the device wheel clock-wise so that the adjuster tube is pulled out.

5) Now, open the both ends of the tab washer of the lock screw and un-screw the lock screw and remove it.

6) Unscrew the leader nut unit.

7) Send the leader nut unit to the leader nut unit dismantling table.

8) Operate the device wheel anti-clockwise and remove the coupler nut pin and release lever to normal position by rotating the wheel clockwise.

9) Extract out traction unit and remove the coupler nut fitted. Send the traction unit to dismantling table.

Traction Unit and Leader Nut Unit Dismantling From Barrel Unit (On Pneumatic Device)

1) Couple the coupler nut to the adjuster tube of the slack adjuster.

2) Place the slack adjuster on the bottom half portion of the clamp system and close the top portion clamp.

3) Operate pneumatic air cock no.1 so that the piston no.1 will hold the slack adjuster in the clamp system fully tight.

4) Insert the pin connecting the coupler nut and pneumatic device levers.

5) Operate air cock no.2 so that the lever will pull out the traction unit from the barrel.

6) Now, open the both ends of the washers of the lock screw and un-screw the lock screw and remove it.

7) Now, unscrew the leader nut unit from the barrel and send it to leader nut unit dismantling table.

8) Release air cock no.2 so that the traction unit will be pushed into the barrel by levers.

9) Remove the pin connecting the coupler nut and levers.

10) Now, extract traction unit and send it to dismantling unit.

11) Now, release air cock no.1 so that the barrel is released in the clamp system. Send the barrel and barrel spring to the cleaning and inspection table.

Traction Unit Dismantling

1) Clamp traction unit lightly in a vice (adjuster tube pointing upwards).2) Remove circlip with pliers.3) Remove Bering dowel sleeve by driving it inwards through traction

sleeve and clutch sleeve.4) Unscrew clutch sleeve with spanner B.5) Separate the traction unit parts from each other.

Note : It is not necessary to separate adjuster tube socket from adjuster tube 41 for cleaning purpose.

Leader Nut Unit Dismantling

1) Clamp leader nut unit lightly in a vice.2) Remove circlip with pliers.3) Remove spring cap and take out the spring, ball race , ball cage and

leader nut.4) Separate the leader nut unit parts from each other.

After dismantling every unit separately the next steps to be followed are :

Cleaning Inspection

Cleaning of Parts

Wash all parts thoroughly in suitable cleaning fluid, preferably by dipping, and with the aid of brush. Remove all visible foreign particles such as dirt and grit and check worn parts according to the wear Units specified. The threads of adjuster nut, leader nut and adjuster spindle should be given special attention.

Test the thread of the adjuster spindle with one of the nuts, the nut lust run freely over the entire length of the thread. Should any damage have occurred, such as for instance a burr or nick, smooth the area with a fine file and wash clean, making sure that all filings are removed.

Inspection of Parts

Give all other parts a thorough visual inspection to detect apparent defects.

1) Ball Bearing

a) Mold the upper and lower races with the ball cage between them and with normal hand pressure the ball cage should not rub against either ball race at any peripheral point.

b) Ensure that the balls are securely housed in the cage and would not fall out.

2) Adjuster Tube Socket

a) Ensure the radius is free of any burrs. Burrs, if any, must be carefully removed by abrasive paste or paper.

b) Replace socket, if its radius edge has worn out flat.3) Adjuster Tube Assembly

a) Ensure that guide bushing and socket are properly tight.

b) In case of any movement of socket or guide bush, the assembly should be dismantled and reassembled.

c) The guide bushing must be locked by the socket screwed on to the adjuster tube and finally secured by spring dowel sleeve. The 6 mm dia. hole for spring dowel sleeve should be drilled on assembly through marked hole on socket.

4) Friction Washer

a) Ensure that the corners of ear of the friction washer are sharp, washer with worn out ears should be replaced.

5) Wire Ring Part

a) Ensure that the wire ring securing the friction washer is snap fitted properly into the recess provided for it.

6) Actuating Sleeve

a) Ensure the chamfer as shown in the fig is free from any burrs. Burrs if noted, must be dressed smooth with abrasive paste or paper.

b) If the chamfer is badly scored, the sleeve should be replaced.

Note : When the actuating sleeve is rejected the corresponding socket should also be replaced to ensure formation of correct matching of re-dressed lap of socket and chamfer on actuating sleeve in assembly which is essential for the function of Slack Adjuster.

c) If the chamfer is slightly scored, the face may be ground and matched with the socket radius to ensure free movement between the two contact area, falling which the same are to be rejected.

d) Insure that the taper face is free from any step formation or recess created by wear and tear. If any such thing is observed as shown in fig the actuating sleeve must be rejected.

7) Clutch Sleeve

a) After assembly of the traction unit, it is necessary to check that the short cone of clutch ring can contact clutch sleeve without being topped by the ball bearing. If the clutch ring abuts on the ball bearing before it can touch the clutch sleeve, the clutch ring must be replaced.

8) Barrel With Barrel Head

a) The assembly must be rejected when the barrel head has worked loose. Tack welding is not recommended.

9) Leader Nut With Dog Pin

a) Ensure that the dog pin is press fit. If loose the pin should be replaced. A hole of size 5±0.18mm should be drilled at a different location on the same periphery and a new standard dog pin should be pressed inside.

10) Leader Nut Flange

a) Ball cage with race under hand pressure should not contact any point of flange due to the groove developed on working. If so, the flange may be reversed and used in assembly.

11) Spindle Sleeve With Bushing

a) Spindle sleeve assembly must be free to move on the adjuster spindle. If the free movement is restricted due to any external damage on the protection tube the same is to be replaced.

12) Adjuster Spindle Part

a) Spindle bend within the space should not be used and must be replaced.

b) Hold the spindle upright with threaded portion above and just engage and leave a good adjuster nut on to it. If the adjuster spindle is good, the nut should move freely down to the bottom of the thread of spindle without any interference. If not, the spindle should be replaced.

13) Adjuster Ear With Adjuster Tube

a) The adjuster ear should be secured on to adjuster tube and locked by lock.

b) In case of thread damage either in adjuster tube or on adjuster ear, the defective part should be replaced.

14) Spring Sleeve

a) When the height as shown in fig.27 is increased to 67 mm. this should be replaced.

b) Any external damage/crack to this item should be replaced.

15) Leader Nut Casing

a) Ensure the chamfer as shown in the fig.28 is free from any burrs. Burrs if noted, must be dressed smooth with abrasive paste or paper.

b) If the chamfer is badly scored, the leader nut casing should be replaced.

Wear Limits

The item given below shall be condemned when it reaches the condemning limit indicated against each.

Adjuster spindle

a) Plank abrasion should not exceed 0.3 mm to be checked with gauge.

b) When replacing a spindle, the corresponding adjuster nut and leader nut also be replaced.

Adjuster nut and leader nut

a) Axial play of worn nuts and new spindle must not exceed 2 mm. Check the threads of the nuts with gauge.

Dimensions of Different Parts

Leader Nut

a) Inside diameter of non-threaded end maximum -- 30.50mmb) Outside diameter of non-threaded end minimum -- 39.00 mm

Adjuster Tubea) Outside diameter must not at any point be less than -- 43.50 mm

Guide Bushinga) Inside diameter maximum -- 29.50 mm.

Barrel Head Parta) Hole diameter maximum -- 46.5mm

Leader Nut Casing

a) Diameter of guide recess maximum -- 40.50mm[Housing for non threaded portion of the leader nut]

Guide Pina) Width of hexagonal guide pin maximum -- 8.50 mm

Actuating Sleevea) Width of slot for guide pin maximum -- 11.50 mm

Spring Sleeve

a) Thickness of the plate of the flange minimum -- 0.80mmb) Height as shown in figure, maximum -- 67 mm

Procedure for Testing Springs

a) First we have to check free height of the springs if it is correct according above table then we have to proceed the next step.

b) Here all springs are tested on pneumatic devices.

c) For any spring we have to place spring below piston and apply the pressure given on the table.

d) Then we have to see that the compressed height should be compressed above or below the red mark.

Springs with following characteristics are suitable for satisfactory working of the Slack Adjuster.

S No Description Part No Compressed

Correspond Minimum

1. Barrel Spring 21 475 143

2. Payout Spring 11 100 58

3. Take up Spring

37 21.5 22

4. Clutch Spring 39 38 300

1) Any spring which does not conform to the above characteristic should not be used.

2) In addition any spring badly rusted, or having compressed coil turns should not be used.

Replacement of Basic Items

The following items shall be replaced irrespective of the condition at the time of POH of Slack Adjuster.

1 Spring Dowel Sleeve 5 Rubber Gasket

2 Lock Washer 6 Spring Dowel Sleeve

3 Seal Ring 1 7 Dog Pin

4 Seal Ring 2 8 Tab Washer

Lubrication

After completing the cleaning and inspection of all parts and before reassembling the Slack adjuster, coat all parts liberally with Lithium base MP-2 grease or equivalent. Approximate requirement of lubricant is 1.2 kg excess grease should not be used.

Reassembling

Every unit is individually assembled and then joined together. Various parts are used in assembling of a SAB. Finally adjuster spindle and control rod are attached to the tested SAB.Traction Unit Assembly

1) Apply grease to the interior portion of traction sleeve.

2) Apply grease to adjuster nut, ball race, baa cage and baa race no2 and place them inside the traction sleeve . place take up spring and ball race inside sleeve.

3) Insert adjuster tube into the actuating sleeve so that it seats on the adjuster tube socket.

4) Insert this assembly into traction sleeve.

5) Apply grease to clutch spring and clutch sleeve and fit them on to the traction sleeve to seat on the actuating sleeve.

6) Now clamp the assembled traction unit on the bench vice and tighten the vice fully.

7) Tighten the clutch sleeve with special spanner till the holes of traction sleeve and clutch sleeve coincides.

8) Insert spring dowel sleeve 6x10mm in to the coincided holes.

9) Insert circlip 45x2.5mm size into the adjuster tube groove.

10) Now fit on ballrace, ballcage and clutch ring on clutch sleeve.

11) Now traction unit assembly is ready.

Leader Nut Unit Assembly

1) Apply grease to interior portion of the leader nut casing.

2) Insert dog pin into leader nut and place leader nut flange on the bottom portion of leader nut.

3) Fit leader nut circlip size 40*2.5mm into leader nut groove.

4) Apply grease to the leader nut and leader nut flange, ball cage , ball race. Place ball cage.

5) and ball race on the leader nut flange. Place this assembly into leader nut casing.

6) Apply grease to payout spring and place it on the leader nut assembly. Apply grease to the spring sleeve interior portion and place it on the payout spring. Place circlip of size 85*4mm on spring sleeve.

7) Now place the leader nut assembly on the machine bed so that the leader nut casing is seated on the machine bed bush.

8) Place the 20mm ms packing piece provide on to the leader nut unit.

9) Open air cock no1 so that piston of device travel down and press against the 20mm packing piece, there by the spring sleeve slides down.

10) Insert properly the circlip into the groove of the leader nut casing with help of plier.

11) Now operate air cock no2 so that the piston travels up fully.

12) Now the leader nut assembly is ready.

Assembled Leader Nut Unit

Reassembling of Traction Unit and Leader Nut unit with Barrel Unit on Pneumatic Device

1) Place the barrel on the bottom half of clamp system and close the top portion clamp.

2) Operate air cock no1 so that the piston no1 will hold the barrel in clamp system fully tight.

3) Apply grease on the barrel spring and insert barrel spring into barrel.

4) Screw the coupler nut on to the traction and insert the traction unit into barrel.

5) Connect the coupler nut and pneumatic device levers by the pin.

6) Operate air cock no2 so that traction unit will be pulled out.

7) Screw the leader nut unit to barrel at other end.

8) Place the tab washer on the barrel hole and insert the lock screw and tighten it.

9) Bend the two ends of the tab washer on the lock screw head.

10) Release the air cock no2 so that the traction unit will be pushed back in to the barrel and traction sleeve touches spring sleeve.

11) Remove the coupler nut pin and un-screw the coupler nut from traction tube.

12) Now release the air cock no1 so that the barrel is released freely in the clamp system.

13) Lift the clamp system top portion and send the fully assembled slack adjuster for final test on rack.

Safety Precautions

The following safety precautions should be observed during overhauling of slack adjuster.

1) The place of overhauling must be clean and free from dust.

2) Ensure that no foreign particle remain inside the sub-assemblies during re-assembly.

3) All rubber gasket, seal ring, washers must be replaced during overhaul.

4) Specified tools and fixtures are used for disassembly and assembly operations.

Testing of Slack Adjuster

After overhauling, testing of slack adjuster in carried out in a test rack for :

Pay-in Test Pay-out Test

a) Attach the adjuster ear to the free end of the cylinder lever of the test rack.

b) Screw the test rack spindle into the Slack Adjuster until the entire length of thread is covered by spindle sleeve and attach the free end of the spindle to the test rack.

Pay-in test

1) Let down the control rod, so that the fork of the rod clasps the adjuster tube of the Slack Adjuster.

2) Apply and release the brake a few times letting the slack Adjuster take up until the correct piston stroke is obtained (until the indicator is within + 5 mm tolerance field of the scale).

Pay-out test

1) Turn up control rod and make two brake applications letting the slack adjuster pay out.

2) Repeat the above pay in and pay-out tests a couple of times.

3) Satisfactorily, dismantle it and check that the parts are placed correctly.

4) The slack adjuster must then be tested once more in the test rack in accordance with the above instruction.

5) After the test is finished, remove the spindle from the slack adjuster.

6) Remove the slack adjuster from the test rack and unscrew adjuster ear.

If test rack is not available

Testing of slack adjuster in brake rigging with hand brake

In case a test rack is not available in the work shop, a test of function of the slack adjuster ought to be carried out after the slack adjuster is installed in the brake rigging and the correct piston stroke is obtained as follows :

1) Place an iron object e.g. a hammer between the brake block and the wheel tread. Make two brake applications after the second application the correct piston stroke should be obtained.

2) Remove the iron object. Make two brake applications. After the first application the piston stroke is too long, but after the second application the correct piston stroke is recorded by the slack adjuster.

Joining of Pull-rod with Adjuster Spindle

1) Arrange for eye ended pull rod of correct length as par the Installation drawing.

2) Join them preferably by electric flash butt welding. If this is not possible, prepare both the ends by tapering to an angle of 30 degree, 25mm.length of both rods and weld the prepared faces by electric arc welding. While welding the following precautions to be taken:

a) Centre lines of both pull rods must lie on one common centre line.b) Provide protective cover over threaded portion of Adjuster spindle to

prevent molten metal falling on threads.

3) Give adjuster spindle a final thorough inspection making sure that the threads are liberally greased.

Assembling of Adjuster Spindle to Barrel Unit

1) Unlock the washer and screw out the adjuster ear.

2) Taka Out the spring dowel sleeve and screw out safety collar.

3) Insert the Adjuster spindle through spindle sleeve, then rotate it clockwise until the spindle comes out through adjuster tube.

4) Assemble the safety collar and spring dowel sleeve. Rotate the spindle anticlockwise until the spindle has come out equal to dimension ‘E’.

5) Slide control rod head with control rod assembly over the adjuster tube.

6) Screw in the adjuster ear with lock washer and tighten up. Lock the adjuster tube by lock washer.

Assembling Of Control Rod

Slide control rod head with control rod on to adjuster tube. Place lock washer on threaded portion of adjuster ear and screw ear into threaded end of adjuster tube.

Painting

Give the slack adjuster a coat of anticorrosive paint, excluding the adjuster tube (visible).

Note : The unthreaded portion of the adjuster spindle should not have a thick coating.

Fitment on wagon for checking

General arrangement showing the fitment of slack Adjuster provided with vacuum brake and Air brake .For the proper working of slack adjuster. It Is essential to ensure that the brake rigging is working properly and ‘E’ dimensions are correct and also we have to check the empty load device.

‘A’ Dimension :

‘A’ dimension is measured between barrel head and control rod head and it is 92mm for manual A Dimension.

For ‘A’ dimension (16 +2/-0 mm for 13t bogie and 22 +2/-0 mm for 16.25t bogie)

a) Ensure the air brake is in fully released condition and all the brake rigging gears are in proper condition.

b) Apply brake three to four times to ease the rigging, by dropping and re-charging the air pressure in the brake pipe

c) Ensure once again that brake rigging is in fully released condition.

If ‘A’ dimension is not correct

a) Remove pin securing the control rod in U bracket.

b) Detach control rod and rotate it to adjust the gap between barrel end face & control rod head as specified in note above. Secure the control rod in U bracket.

c) Apply brakes two to three times.

d) Check the ‘A’ dimension using the gauge.

e) Recheck dimension ‘A’ with brakes fully released after every brake release.

f) Lock the control rod head firmly with check nut and tooth lock washer.

g) Secure pin with split pin.

Check ‘A’ dimension. This should be as follows for different wagons.

1) 50 ± 2 mm for BOX,BCX,BCXC III, BTPGL ,MBTPS type of wagon.

2) 70 ±.2 mm for BOXN,BCN,BRN,BOY, BTPN type Of wagons.

3) 60 ±.2 mm for BFKI wagons.

4) 20 ±2 mm for B0BRN wagons.

‘E’ Dimension :

a) If slack is in excess beyond the capacity of slack adjuster (‘E’ dimension 375+25mm) there won't be any slack take up provision in the slack adjuster and slack adjuster will only act as strut/pull rod. This is because of brake shoes and wheel wear reaching their condemning limit/near condemning limit. In such cases the `e' dimension can be restored by adjusting link provided on the bogie frame head stock.

b) Measure ‘e’ dimension i.e. distance between protection tube end and mark on adjuster spindle using measuring stick after two or three brake application. It should be set to nearly to its maximum limit i.e. 575±25mm.

Empty/Load Device :

Traction between the wheels and the rail is directly proportional to the weight on the wheels. The amount of traction determines the amount of braking that can be applied without sliding the wheels. Sliding wheels develop flat spots within a few feet. Train cars have a large weight difference between the loaded condition and the empty condition, especially modern coal hoppers and grain cars.

The maximum braking effort of a car must be designed so that when in emergency (when the highest brake cylinder pressure is obtained) the EMPTY car will not slide its wheels. Unfortunately this means a heavily loaded car is under braked even in emergency. A way was needed to allow higher brake cylinder pressures on loaded cars than on empty cars.

The first step was to put larger reservoirs on the cars so that the traditional 2.5 to1 ratio of reservoir volume to brake cylinder volume was greater. This will result in higher brake cylinder pressures for any given brake pipe reduction. The problem is that higher pressure will slide the wheels of an empty car. So a pressure limiting valve is attached to the brake cylinder which will vent any excessive pressure to the atmosphere thus limiting braking effort. The exhaust of this limiting valve is open to atmosphere on an empty car allowing it to vent excess pressure. On a loaded car it is closed off so it cannot vent any pressure from the brake cylinder thus taking advantage of the higher pressure which results in higher braking effort.

The closing or opening of the limiting valve exhaust is controlled by a load/empty sensing arm. The pressure limiting exhaust close off valve is mounted on the car frame just above the truck frame. One end of an arm is

attached to the close off valve and the other end rests on the truck frame. If the car is EMPTY the car body rides high on the springs and the arm moves the close off valve to the open position allowing the limiting valve to vent excess pressure. A LOADED car rides low on the springs and the arm is pushed up, moving the close off valve to the closed position, thus preventing the limiting valve from venting the higher brake cylinder pressure.

Checking Empty Load Device and Empty Load Tie Rods :

1) Put the lever arm in empty position as shown in fig. 4 and hear the clear click sound.

2) Apply the brake. If vacuum / air pressure is not available apply band brake fully.

3) Tap empty tie rod pins. These should be tight, if so the adjustment is correct.

4) If load tie rod pins are found tight the adjustment is wrong as the sleeve nut has been tempered with.

Adjustment Of Empty Tie Rod :

1) Ensure brake rigging is fully released (Hand brake also).

2) Insure horizontal levers can move freely.

3) Inspect tie rods and aleeve nut for Mechanical damage.

4) Put lever arm in loaded position.

5) Shift lock nuts and washer as far away fron aleeva nut as is possible.

6) Rotate sleeve nut in direction. This will shorten empty tie rod fully.

7) Rotate sleeve nut in direction. This will lengthen the empty tie rod.

8) Stop rotating the sleeve nut when the end of the ‘LIVE LEVER’starts moving.

9) Then carry out test as mentioned above.

10) Tighten lock nuts with washers. This should be done with brake still on.

11) Bend over lock nut washer ( Z shape).

Note : If test fails and load tie rod pins are still found tight, empty load davice operating pawl (catch) may be broken. Replace empty load device.

Safety Precautions

1) Always use wedge between wheel and rail before application and release operations for setting and measuring A and e dimension to prevent rolling of coach.

2) Ensure no part of the worker’s body is in touch with moving brake rigging gears during application and releasing of brakes.

3) Do not touch or hold slack adjuster barrel while it is in motion.

4) Before setting any dimension ensure wear of brake shoe does not exceed to its minimum permissible worn limit (i.e. thickness of the shoe should not be less than 20 mm).

5) There won't be any slack take up provision in the slack adjuster and slack adjuster will only act as strut/pull rod. This is because of brake shoes and wheel wear reaching their condemning limit/near condemning limit. In such cases the `e' dimension can be restored by adjusting link provided on the bogie frame head stock.

How The Slack Adjuster Operates

Control distance ‘A’ measured between control rod head 26 and barrel 22 when the brake is fully released corresponds to the correct slack. If the slack is correct, as the brake is applied, head 26 touches barrel 22 at the moment when the brake shoes start to apply against the wheels and no adjustment will then take place.

If the slack becomes too large, as the brake is applied, head 26 pushes the barrel 22 and at the moment when the brake shoes apply, the distance between barrel 22 and adjuster ear 28 is increased by an amount corresponding to the excess of slack. Clutch B is released and leader nut 35 follows the position of barrel 22 , rotating on spindle 23 to remain in contact with the left hand end of the barrel. When the brake is released, nut 35 is locked against the left-hand end of barrel 22 and spring 21 causes adjuster nut 36 to rotate on spindle 23 towards nut 35. This movement of nut 36 on spindle 23 shortens the Slack Adjuster and thus adjusts the slack to its correct value.

If the slack becomes too small, the first subsequent brake application releases clutch C and causes nut 35 and barrel 22 to rotate towards head 26 until stopped by it. The distance between nuts 36 and 35 has been shortened by an amount corresponding to the deficiency of slack. At the start of next brake application, nut 35 is locked in its new position on spindle 23, and pay-out spring 11 pushes nut 36, rotating on the spindle until normal distance

between the two nuts have been restored. The slack Adjuster is in this way lengthened and the slack adjusted to its correct value.

Trouble Shooting

Conclusion

Though the SAB section is small in wagon assembly sections but due its parts, its function and its working make this to compete with other sections (wheels, bogie). It is one of major function in brake application. The most interesting features in this SAB is it consists of 49 parts and the whole over- hauling process is done manually.

References

http://www.mpi.mb.ca/PDFs/AirBrakeManual/ABM_Section8.pdf

http://en.wikipedia.org

http://www.sanrok.in/Slack_Adjusters.htm

http://www.escortsgroup.com/images/brand_and_products/ railway_equipments/slack_adjuster.pdf

http://www.nyab.com/pamphlets/IP178.pdf

http://www.serailway.gov.in/HQ/mechanical/FREIGHT/Freight %20information/MISC/Wagon%20dimensions/G%20-Mannuals/G-92%20(SAB)/SAB600-1.doc

http://www.irimee.ac.in/rst/know/coachman/Vacuum%20brake %20system.pdf

http://203.176.113.182/RDSO/wagon/ven_regis/list_specification.doc