CHAPTER IV
MAINTENANCE AND OVERHAUL SCHEDULES OF EMUs 30400 General
Para 30300, 30301 and 30303 will be applicable to EMU mutatis-mutandis as well.
30401 Scheduled Inspection
The motorman, after overnight stabling of EMUs, while taking over shall ensure draining off of the air reservoirs to expel accumulated water.
a) The Maintenance and Overhaul Schedules to be followed for AC EMUs will generally be as under- i) Daily Inspection
ii) Trip Inspection (IT)
iii) Monthly Inspection (IA)
iv) Quarterly Inspection (IB)
v) Half Yearly Inspection (IC)
vi) Intermediate Overhaul (IOH)
vii) POH
b) The Daily Inspection is essentially an inspection to be carried out by the 'Running Section. It may also be carried out in a shed if convenient or at an outstation when the unit is stabled overnight away from the shed. IT, IA, IB, IC and IOH should be carried out in the homing shed for each EMU whereas POH should be carried out at the workshop nominated for this purpose for each railway.
c) The details of work to be. done during each schedule require periodical review in the light of local conditions and operating experience with each type of EMU. The details given in Annexure 4.01 are for guidance only.
30402 EMU Fitness Certificate
Instructions contained in Chapter III (Para 30304) for locos will apply mutatis-mutandis for EMU as well. (Proforma 4.01).
30403 Testing of Air Brakes
A brief description of Electro-pneumatic brakes is given in the Annexure 4.02, Test procedure for the air brakes is however given below:
1. Before an EMU train is issued for traffic from a shed after scheduled inspections, POH or unscheduled repairs, a supervisor of the M5 section should test the air brakes of the complete train formation. The brakes should be tested from the driving cabs at both ends of the train formation.
A list of items to be checked in the case of Westinghouse brakes of ICF EMUs is given below for guidance. Detailed check lists on similar lines should be prepared for different types on EMUs and units fitted with Knorr brakes. These should be in the form of printed forms. The completed forms duly signed by the supervisor of M5 should be preserved in the PPO for a period of six months.
Check :
i) that all inter-car hose connections are made and all coupling, isolating the drain cocks are in the normal position.
ii) that MR pressure is maintained between 5.8 and 7 kg/cm2 and the compressors start and stop respectively at these values of pressure.
iii) that when the Driver's control switch, EP brake switch and isolating valve switch are put on, the green indicator light in the driving cab glows.
iv) that the brake pipe pressure builds upto 4.57 kg/cm2 in approx, 90 seconds.
v) that when the brake controller handle is moved from position 1 to position II step by step ( a minimum of 6 steps should be used), the brake cylinder pressure builds up to the value proportional to the handle position and is maintained at this value by the self-lapping mechanism. In position II the pressure should be 3.5 kg/cm2 for cast iron brake blocks and 1.5 kg/cm2 and 2.0 kg/cm2 for motor and trailer coaches respectively provided with composite brake blocks. When brakes are applied the orange lamp should light-up to prove the application of brakes in all the bogies.
vi) that when the handle is moved back from position II to position I step-by-step ( a minimum of 6 steps should be used) the brake cylinder pressure is reduced to the value corresponding to the handle position and is maintained at this value by the self-lapping mechanism.
vii) that when the handle is quickly moved from position I to position II, the brake cylinder pressure will rise to the maximum set value.
viii) that on moving the controller handle from position II to position I, the brake cylinder pressure drops to zero.
ix) that during EP application and release the brake pipe pressure is not affected.
x) that when controller handle is moved from position I to position III and then to IV, the brake pipe pressure drops gradually with sound of escaping air, and brake cylinder pressure rises correspondingly. When the controller handle is moved back to III, the drop in brake pipe pressure and the rise in brake cylinder pressure should be arrested.
xi) that when controller handle is moved from position I (after allowing full BP pressure to build up) quickly to 'Emergency' position V, brake pipe pressure is reduced rapidly and brake cylinder pressure rises to slightly more than 3.9 kg/cm2 within 2.5 seconds.
xii) that with the brake controller in the driving cab in position II the brake cylinders on each bogie are functioning and there is no leakage. Check also that the manual release valves have wires attached to them to facilitate operation from the sides of the train.
30404 Maintenance of Vacuum Brakes
A brief description of vacuum brakes is given in the Annexure 4.03. Instructions regarding maintenance of vacuum brakes are contained in TXR Manuals, the salient points of which are summarized below:-
Periodical Examination of Vacuum Brake Gear:
1. All vacuum brake cylinders shall be lowered, examined, cleaned and necessary repairs and renewals of rubber fittings effected, once in every 12 months. The code of the examining station making such an examination, the date and words "EXD" shall be painted in white on the cylinder thus : EXD-JTJ-10-1-1970.
2. In fitting up vacuum brake cylinders it is important to see that the lever of the brake shaft is exactly parallel with the trunnions on which the cylinder swings so that no side or cross strains are set up.
3. When putting a rolling ring on to a piston, care should be taken to ensure that the ring is not twisted. Around the ring a seam line will be found, which should lie evenly and horizontally all-round when in the groove. The correct alignment can be secured by pulling the ring slightly away from the drum of the piston on the opposite sides with the thumb and finger of each hand. A good rolling ring is one which when allowed to hang from the finger will hang straight. Whereas, if a ring twists when being suspended it should be rejected. An air tight fit is made between the piston and cylinder by the rolling ring.
4. (i) The stuffing box, gland and brass bush should be examined to ensure that they are intact in all respects. Excessively worn gland will cause air leak below the piston and hence should be renewed.
(ii) The gland is held in position by a brass ring having groove at top and bottom edges. When the stuffing box is tightened the rubber gland is squeezed into the grooves. On creating vacuum, the gland packing gets tightened, due to atmospheric pressure acting over the outside of it.
(iii) The brass bush must be examined for wear, as this part has the important function of maintaining the piston rod steady in its movement. When the bush is worn excessively the travel of the piston becomes unsteady and jerky.
5. The joint ring between the flanges of the. vacuum chamber and cylinder should be in correct position. To retain the joint ring in exact alignment while the cylinder is being lifted into position, clips made out of split pins could be used.
6. While tightening up the joint, the nuts should be screwed up evenly all-round and not too tightly or haphazardly.
Unequal tightening of the nuts may cause the cylinder being drawn out of shape. This should be avoided. The correct procedure is to tighten up opposite nuts while assembling. On creating vacuum the nuts should be tightened up finally.
7. The release valve has a flat valve head which normally remains seated cutting off all direct communication between the body of the valve and the vacuum chamber or top of the piston. This can be opened by pulling the release valve lever by hand. A defective seating washer or a diaphragm washer will allow air to enter above the piston when vacuum is destroyed and the vacuum cylinder will not function properly. Such defective washers should be changed.
8. Cleaning: When dismantling a cylinder for cleaning all rubber parts should be removed and kept clear of oil or any other solvent likely to damage the rubber. French chalk may be used for cleaning or dressing the rubber fittings, or the working surfaces of the cylinder and piston.
If it is found necessary to use a solvent to remove dirt from working surfaces of the metal parts all traces of this solvent must be removed before replacing rubber parts, otherwise deterioration and failure in service are liable to occur. These working surfaces are coated with a special red rust-preventing varnish and the solvent must be of a nature which will not affect this varnish. Emery paper or cloth should never be used to clean the piston and cylinder.
9. The piston travel should be limited to a maximum of 4" (100 mm) to ensure effective brake power.
Annexure 4.01 1. Daily Inspection
During this inspection, the Engine Examiner should- ,
a) carry out detailed checks in regard to any unusual occurrence reported by Motormen in the log book.
b) visually inspect the auxiliaries for satisfactory starting and operation.
c) feel by hand that the temperature of axle bearings is normal.
d) visually inspect mechanical components like traction bars, pendular suspension, springs, dampers etc. and the brake rigging to detect any abnormality; and
e) check the controls and indication and alarm circuits for correct functioning. Every unit should be checked under the supervision of a Train Examiner (Traction), generally during night stabling. Similar inspection (in addition to attention to the unscheduled repairs) should also be carried out in a unit called to the shed for unscheduled attention, before it is declared fit for traffic.
The important items to be checked are :
i) Tap all wheels to detect for loose tyres and tyre cracks. Visually inspect all wheels for defects such as cracked tyres, flats etc. and also bogies and running gear for any abnormalities.
ii) Feel all axle boxes by hand immediately after stabling. Check axle box covers, iii) Check axle guide helical springs for breakage.
iv) Check brake blocks. Renew badly worn or cracked blocks. Adjust slack adjusters, if required, to obtain clearance of 12 mm between brake blocks and wheels. Look. for broken parts of brake rigging. Check the application of the brakes.
v) Check bolster helical springs visually.
vi) Check look-out glasses and head code glasses. Clean look-out glasses,
vii) Cushions to be checked and badly damaged cushions to be replaced,
viii) Test check passenger alarm chain for operation from at least 2 coaches in a train,
ix) Visually check the pantographs for any defect.
x) Check oil-level of air compressors and suspension bearings, top up if required,
xi) Check operation of automatic drain valve of main reservoirs. Drain all other reservoirs,
xii) Test the horns at both ends.
xiii) Check for noticeable air leakages in compressed air system.
xiv) Check inter-unit air hose couplings.
xv) Test wind screen wipers (in rainy season).
xvi) Test brake controller at each driving position for correct operation. Particularly observe the brake-pipe pressure.
xvii) Test deadman's device in each driving cab
xviii) Test pantograph raising and lowering push buttons in each driving cab.
xix) Check Master Controller in each driving cab.
xx) Test auxiliary compressor.
xxi) Check battery voltage and trickle charge current.
xxii) Test signal bells.
xxiii) Clean the compartments and cushions. Clean driving cabs.
xxiv) Test headlights, flasher lights and tail lights including emergency lights.
xxv) Check that all the safety straps are in position.
2. Trip Inspection
1. The chief object of this inspection is to renew the worn-out brake blocks if necessary usually at Intervals varying from 5 to 8 days particular attenation being paid to differential rate of wear between motor coaches and trailer coaches.
2. The periodicity of this inspection will depend upon a number of factors such as daily Kilometrege, proportion of 'fast' and 'slow' trains, quality of brake blocks etc. The periodicity should be decided by each Zonal Railway depending upon its actual operating requirements. It is essential to ensure renewal of brake blocks before they reach condemning thickness.
3 In addition to replacing brake blocks and the items listed against Daily inspection, carry out the following checks:
i) Visually inspect the bogie frame for cracks or other damages, ii) Check helical springs of axle guide for breakage, iii) Check axle guide for excessive oil leakage, iv) Check tightness of axle guide oil filling cap.
v) Check axle guide safety strap.
vi) Inspect axle suspension bearings of traction motors and check oil levels, particularly check pressure and tightness of drain plug and filler cap. Tighten bolts.
vii) Check gear-box for lubricant level and tighten bolts, viii) Adjust brake pull rod, rigging and slack adjusters.
ix) Inspect brake rigging components thoroughly particularly bushes, pins, split-pins and cotters, x) Check centre pivot. xi) Inspect 'Schaku' couplers for cracks, deformation and damage.
xii) Inspect buffers and lubricate buffer plungers.
xiii) Lubricate screw couplers.
xiv) Check all doors and windows, door handles, foot-steps, window safety bars and hand rails.
xv) Check that protective screen for look-out glasses, where provided, is properly secured.
xvi) Clean driving cab window panes and swab clean cushions.
xvii) Inspect pantographs for flash-marks, wear of strips and cleanliness of insulators. Lubricate articulation joints, bearing joints and pans.
xviii) Check compressor crank case breather pipe.
xix) Check oil level of auxiliary compressor and top up, if required.
xx) Check operation of EP contactors and reverses by manual operation of the control magnet valves.
xxi) Check transformer oil level and top-up if required. Check transformer for oil leakages.
xxii) Check colour of silica gel and replace if required.
xxiii) Open inspection covers and make a quick inspection of traction motors for flash-marks, broken brushes, damaged pig-tails or other damages.
xxiv) Check that the auxiliary machines are running without any unusual noise.
xxv) Make a quick examination of all electro-magnetic contactors and relays.
xxvi) Make a quick visual examination of air-blast circuit breaker and test its operation.
xxvii) Battery: Clean vent holes of filler caps, check intercell and main connection, record specific gravity and voltage of pilot cells, top up with distilled water if required and smear cell connections and terminals lightly with petroleum jelly after cleaning.
xxviii) Check and attend to all defects of lights and fans.
xxix) Clean underframe equipment particularly at locations where fire is possible due to accumulation of oily matter; also clean filters, as required.
xxx) Check the correct operation of RGCP. xxxi) Check self lap feature of the EP brakes.
3. Monthly Inspection (IA)
In addition to the items listed against Daily and Trip inspections, the main items to be attended to during Monthly Inspections are - .
i) Measure tyre (root wear and flange wear) and record. (Refer to Annexure 3.01 item F) and reprofile if required and ensure that variation of diameters are within permissible limits.
ii) Check axle boxes for leakage of grease, specially from back dust-guard and for any cracks or other damages.
iii) Inspect reversible gear-box of speedometer.
iv) Check suspension bearing housing fixing bolts for tightness.
v) Check gear-case securing bolts for- tightness.
vi) Check motor coach friction damper liners and pads.
vii) Check shock-absorbers for oil leakages.
viii) Check centre-pivot bottom cover with its fixing bolts and nuts.
ix) Inspect side-bearers for excessive oil leakage.
x) Inspect buffers for cracks and damages and tightness of fixing bolts.
xi) Check cattle guard for security of fastening, deformation and clearance from rail level.
xii) Check all seats, luggage carriers, strap hangers and door locks.
xiii) Check for leakages from roof (particularly prior to and during rainy season).
xiv) Check that hand-brakes are functioning effectively.
xv) Gauge and change if necessary, pantograph strips and clean all roof insulators.
xvi) Inspect and clean suction strainer and centrifugal dirt collectors.
xvii) Overhaul and. test reducing valves and check that correct brake pipe pressure of 4.57 kg /cm2 is built up.
xviii) Check complete compressed air system for leakage.
xix) Test EP, Auto and Emergency application from each driving position and brake cylinder pressure in each coach. Check Guard's Emergency valves in driving cabs.
xx) Remove the arc chutes and inspect all EP contactors for flash-marks, contact wear, contact wipe etc. Check for air leakage at control valves. Lubricate cylinders.
xxi) Check pressure in control air reservoir, xxii) Check operation of all pneumatic governors.
xxiii) Check reversers for operation, finger pressure, wear of contacts, functioning of auxiliary contacts and for air leakage at magnet valves.
xxiv) Inspect silicon rectifier cubicles and clean cubicles with dry compressed air. xxv) Check cell-check device.
xxvi) Check traction motors for condition of commutators, arcing homs, brush holders, wear of carbon brushes and condition of earth-return brushes. Renew brushes, if required.
xxvii) Examine all other DC motors also as above.
xxviii) Lubricate the bearings of auxiliary motors.
xxix) Clean air intake filters for traction motors and compressors.
xxx) Check tightness of all main cable connections.
xxxi) Check the contacts and auxiliary contacts of circuit breakers.
xxxii) Check for functioning of all indication circuits and lamps.
xxxiii) Check voltage stabilizer.
xxxiv) Check all lights and fans individually and test emergency lights.
xxxv) Check the speedometers.
xxxvi) Wash coaches internally and externally by hand scrubbing.
xxxvii) Check head light focussing.
Train formation should finally be checked by El and Ml sections before release for traffic.
4. Quarterly Inspection (IB)
Items given below are required to be attended to in addition to the items listed against Daily, Trip and Monthly Inspections -
i) Check all axles with ultrasonic flaw detector.
ii) Check distance between wheel faces using prescribed gauge.
iii) Check axle guide oil level.
iv) Check condition of axle guide spring lower rubber pads.
v) Check condition of speedometer reversible gear box. v
vi) Traction motor suspension bearing lubrication pads to be checked.
vii) Measure and record radial and lateral clearances of suspension bearings.
viii) Inspect traction motor nose suspension bolts.
ix) Inspect bogie frames, swing links and bolsters carefully, particularly welded, rivetted and bolted joints.
x) Check friction damper spring assembly.
xi) Check compressed height of swing bolster springs.
xii) Inspect draw-gear rubber pads. .
xiii) Uncouple 'Schaku' couplers and inspect the assembly. Lubricate the couplers as prescribed.
xiv) Measure and record buffer heights.
xv) Body panels to be checked for rust, corrosion and damage.
xvi) Check passenger alarm device in each coach.
xvii) Clean the suction strainers of auxiliary air compressor.
xviii) Inspect all brake cylinders; tighten foundation nuts.
xix) For all EP contactors check air gap between main contacts, auxiliary contacts and spring pressure of auxiliary contacts. Clean all insulating surfaces. Check magnet valve stem with condemning gauge.
xx) Check reverser and changeover switch "WCO
xxi) In silicon rectifier cubicles, slide out each rectifier tray and clean the cooling fins. Clean all air ducts, check power connections, check capacitor for oil leakage and inspect HRC fuses, particularly terminal connections.
xxii) Open and inspect Master Controllers. Wipe dry all insulating surfaces and check contacts, xxiii) Clean supporting insulators and check tightness of connections of transition resistances.
xxiv) Clean traction motor brush-holder insulator and check earth-return brush-gear. Check junction box connections for tightness.
xxv) Check main compressor foundation bolts for tightness.
xxvi) In all electro-magnetic contactors check the air gap between contacts, conditions of flexible shunts, knuckle spring pressure and hinge pins.
xxvii) Inspect all push button switch contacts and terminal connections.
xxviii) Check all knife switches.
xxix) Check current limit relay LT supply continuity.
xxx) Inspect voltage stabilizer transformer.
xxxi) Clean headlight reflector.
xxxii) Inspect commutator and carbon brushes of all fans. Renew carbon brushes if required.
xxxiii) Examine axle boxes. If required change the grease. (This item is normally required to be done during every third IB).
5. Half Yearly Inspection (IC)
In addition to the items listed against the earlier inspections, the important items to be attend to are i) Check pantographs for upward pressure.
ii) Renew oil in compressor crank-case and change the oil filter element assembly. Check oil pressure, iii) Decarbonize the valve assembly.
iv) Renew crank-case oil of auxiliary compressor.
v) Safety valves in compressed air system including brake cylinder safety valves to be tested.
vi) Check the suspension arrangement of all under-slung equipment.
vii) In the brake controller, check self-lapping mechanism for correct functioning, regrease fulcrum pins and rollers and examine moving and fixed contacts.
viii) Clean and regrease pilot valve in Master Controller.
ix) Test and adjust operating pressure of all pneumatic governors.
x) Check the condition of cones and rollers of all EP contactors, measure knuckling springs tension, renew Gaco washers and inspect flexible shunts. Check tightness of power connections.
xi) Attend to reverser and changeover contactor WCO as above.
xii) Test oil Sample from conservator, reactor tank and transformer tank of main transformer for dielectric strength and filter the oil If BDV is below 40 kV for one minute.
xiii) Disconnect all inter-vehicular couplers and examine male and female pins.
xiv) In the main rectifier cubicle clean all insulators and examine for cracks. Check individual diodes for tightness with a torque wrench.
xv) Examine Master Controller, lubricate interlocking mechanism and notching cam roller, check contact gap, contact pressure and cam to roller gaps.
xvi) Check traction motor brush spring pressures. Lubricate armature bearings.
xvii)In MG set check bearings for grease leakage and lubricate bearings.
xviii) Overhaul and test all EP brake valves replacing all rubber component on a complete unit basis.
6. Intermediate Overhaul (IOH)
The following items should be attended to in addition to the items listed against earlier inspections -
i) Reversing gear-box for speedometer to be overhauled and speedometer to be tested on test bench.
ii) Check 'Schaku' couplers for wear and damage and lubricate.
iii) Overhaul servomotor of pantograph and check all adjustments.
iv) Overhaul and test pantograph EP valves.
v) Remove main and auxiliary compressors and overhaul on bench. Test volumetric efficiency.
vi) Overhaul and test brake cylinder.
vii) Overhaul the motors of all AC and DC auxiliaries.
viii) Remove air blast circuit breaker, overhaul and test on bench.
ix) Check the setting of all relays and test their operation manually. x) Overhaul all coach fans.
xi) Remove battery set to battery room, examine carefully and subject the set to two cycles of charge and discharge. Take capacity test at normal rate of discharge.
xii) Doors, windows and seats to be checked individually and all defects attended to. Upper class cushions to be repaired and badly damaged cushions to be replaced.
7. Periodical Overhaul (POH)
The POH of EMUs should be carried out in the nominated workshop. The work content and procedure to be followed should be on the same lines as for locos (Item D of Annexure-3.01 of Chapter 3).
8. Mechanical Safety Checks
The Train Examiner of EMU coaches will generally follow the manual and guides of TXR as modified from time to time for application to EMU coaches. The principal clearances as mentioned in (Item F of Annexure-3.01 of Chapter 3) should be checked.
9. Rebuilding and Recabling of EMUs
Activities as mentioned in (Item E(l) of Annexure-3.01 of Chapter 3) above may be carried out on EMUs during every 4th POH and activities mentioned in (Item E(2) of Annexure-3.01 of Chapter 3) may be carried out during every 8th POH.
Annexure 4.02 ELECTRO-PNEUMATIC BRAKES
1. All BG EMU stock have been provided with 'self-lapping electro-pneumatic combined with automatic' compressed air brakes. Two makes of equipment are in use viz. Westinghouse and Knorr-Bremese. Though the details of equipment differ appreciably, both systems are quite similar in principle. The description given below pertains mainly to the Westinghouse equipment provided in ICF-built EMUs.
2. Electro-pneumatic braking is normally employed for service stops. The 'automatic brakes' are used under the following circumstances-.-
(a) For automatic application of brakes on both halves of a train in the. event of a parting.
(b) For application by the Guard in an emergency.
(c) For automatic application due to operation of the dead-man's device.
(d) For service stops by the Driver in the event of failure of control supply for EP brakes.
3. When Driver makes an emergency application both EP and Auto brakes apply.
4. The main components of the equipment are as under-
(a) A main reservoir system consisting of a compressor in each motor coach feeding into main reservoirs on motor coaches and supplementary reservoirs on trailer coaches interconnected from end to end of the train by a main reservoir pipe with flexible couplings at ends of coaches. The main reservoir is maintained at a pressure of 5.8 to 7.00 kg/cm2 by means of pressure governors controlling each compressor. All the compressors in a train are synchronized to start and stop together.
(b) A 'brake pipe' from end to end of the train with-flexible inter-connections between coaches. The pressure in this pipe is maintained at 4.57 kg/cm2 to keep the automatic brakes released.
(c) A 'brake unit' in each coach consisting of the control valves for control of EP and auto brakes.
(d) The brake cylinders on each bogie with automatic slack-adjusters and associated brake rigging. Usually the number of brake cylinders is four per bogie on motor coaches and two per bogie on trailer coaches.
(e) A brake controller in each driving cab. The controller in the driving cab in use being made operative by means of an 'isolating valve switch' operated by the Driver's key.
(f) A brake application relay in each driving cab, the one in the operative cab responding to the operation of the brake controller to control the supply to the brake control train wires carried along with the other control wires in the inter-vehicular couplers.
(g) Five train wires, viz. EP supply wire, brake application wire, brake holding wire, brake indication wire and EP return wire.
(h) A warning system to indicate to the Driver if EP brakes have applied and to warn him if a failure takes place.
(i) A pilot valve and emergency valve to operate the brakes if the deadman's device is released,
(j) Isolating cocks, pressure gauges and control switches.
(k) Release valves for manual release of brakes in individual bogies.
5. Each coach has an 'EP brake unit' which houses the control valves for both EP and auto-brakes. The "pipe-bracket' arrangement is used whereby the valves are bolted on to a casting which has the requisite inter connections between valves by means of cored passages in the casting itself, the only external pipe connections being from the main reservoir and brake pipes and to the brake cylinder and atmosphere.
6. The brake controller handle has five positions as under-
(a) I ................................. Release and Running.
(b) II ............................... Full service EP.
(c) III .............................. Lap(for auto application)
(d) IV ........................... . Service automatic.
(e) V .............................. Emergency.
Lower brake cylinder pressures with self-lapping feature as explained later are obtainable for intermediate positions of the handle between positions 1 and II, the actual brake cylinder pressure being dependent upon the degree of handle movement away from position I.
7. Fig 4.01 is a block diagram explaining the functioning of the EP brakes. When an EP application is to be made, the controller handle is moved from position I towards position II. First the holding train wire is energized which energizes the holding magnet valves throughout the train, thus closing the exhaust from the brake cylinders. The application valves are then energized via the application train wire. This causes compressed air to flow to the brake cylinders from the main reservoir pipe, the rate of flow being controlled by a choke (not shown in the figure). If the application valve remains energized, the pressure in the brake cylinder 2 builds up to 3.5 kg/cm2, any rise of pressure beyond this value being prevented by the "limiting valve.
8. Between positions I and II the self-lapping mechanism controls the brake cylinder pressure. Fig 4.02 shows the self-lapping mechanism schematically. Movement of the controller handle towards II compresses a spring in a small control cylinder, the amount of compression depending upon the degree of handle movement. This spring acts on a piston at the back of which air pressure form the brake cylinders of the leading bogie is applied. When the brake cylinder pressure exceeds the value corresponding to the controller handle position, the mechanism de-energizes the application train-wire, thus limiting the brake cylinder pressure to the value corresponding to the handle position. If the brake-cylinder pressure dropson account of leakage etc. the application wire is re-energized. If the handle is moved backwards, the holding wire is de-energized till the brake cylinder pressure drops to the required value. The self-lapping mechanism thus automatically controls the brake cylinder pressure at a definite value corresponding to the handle position and enables graduated application and release, in position II and V the application and holding circuits are energized by 'positive acting' contacts bypassing the self-lapping mechanism, the pressure then being limited by the limiting valve as explained earlier.
9. Two indication lamps are provided on the Driver's desk-a green lamp to indicate that EP brake control supply is available and an orange lamp which lights up when brake application is made if pressure has built up in all the bogies, which is detected by a pressure switch, the pressure switches in all the coaches being connected in series. The extinguishing of the green lamp indicates total failures of EP brakes necessitating use of the automatic brakes to control the train. Failure of the orange lamps to light up when brakes are applied indicates partial failure of the EP brakes. The Driver has then to be very vigilant and should be prepared to control the train, if required, by using auto brakes.
10. Fig 4.03 is a block diagram explaining the function of the automatic brakes. When the brake controller in the driving cab is in position I and the controller is put into operation by putting on the 'isolating valve switch', compressed air is fed to the brake pipe from the MR pipe via a reducing valve in the brake controller which ensures that the pressure in the brake pipe is built up and remains steady at 4.57 kg/cm2.
The vital component in the automatic brake system is the 'triple valve' which forms a part of the EP brake unit in each coach. Its functions are -
(a) When pressure in the brake pipe is 4.57 kg/cm2, it opens the brake cylinder to atmosphere thus releasing the brakes and at the same time connects the brake pipe to an Auxiliary Reservoir in each coach storing compressed air at a pressure of 4.57 kg/cm2 in the Auxiliary reservoir.
(b) When pressure in the brake pipe is reduced either voluntarily by the Driver or the Guard or due to parting of train or operation of the deadman's device etc., it closes the exhaust from the brake cylinder and connects the auxiliary reservoir to the brake cylinders, allowing the stored air in the reservoir to flow into the brake cylinders. The volume of the auxiliary reservoir is so chosen that the maximum pressure in the brake cylinders is limited to 3.5 kg/cm2. The triple valve also has a lap' position whereby it is possible to control the brake cylinder pressure to values below 3.5 kg/cm2 by holding the brake pipe pressure at intermediate values making use of position III on the brake controller.
(c) When the brake pipe is recharged by moving the controller to position I. the triple valve returns to the position indicated in (a), thus releasing the brakes and storing air in the auxiliary reservoir in readiness for the next application.
Not shown in Fig 4.03 is a 'triple valve stabilizing valve' which ensures that the triple valve does not react to small pressure pulsations.
11. In position V (i.e., 'emergency') of the brake controller, both EP and auto brakes apply together. Rapid application of the automatic brakes is obtained by quick venting of the brake pipe to atmosphere. A safety valve in the brake unit on each coach prevents excessive pressure in the brake cylinders. This valve is normally set at 3.9 kg/cm2.
12. Release of the deadman's device by the Driver results in quick venting of the brake pipe to atmosphere via an 'emergency valve1 resulting in full auto application.
13. A valve is provided in each driving cab to enable the Guard to vent the brake pipe to atmosphere and thus cause brake application. A gauge is provided close to this valve to indicate the brake pipe pressure to the Guard.
14. A pressure switch usually called the control governor' connected to the brake pipe prevents application of power to the traction motors till the brakes are kept ready. This control governor opens and cuts off traction control supply if the brake pipe pressure is reduced.
15. A 'duplex' pressure gauge is provided in the driving cab to indicate to the Driver the pressure in the main reservoir and brake pipes. Another duplex gauge indicate to him the pressure in the brake cylinders of the two leading bogies.
16. Isolating cocks are provided to isolate a defective brake unit form the MR and brake pipes and also to isolate brake cylinders in individual bogies.
17. The brake cylinders are equipped with automatic slack-adjusters to take up the slack in the brake rigging with wear of brake blocks, thus ensuring fairly constant piston stroke and obviating the need for manual adjustment of the brake-rigging between visits of the units to the shed. This is an essential feature of brake equipment for suburban services, when the brake block wear is quite high on account of frequent application of brakes.
18. The Knorr system is quite similar to the equipment described above. In this system, however, the automatic brakes become operative automatically on failure of the EP system. With this arrangement the brake controller has only three positions viz., release", 'full service application' and "emergency".
 Annexure 4.03 VACUUM BRAKES
1 Vacuum brakes are provided in some EMU (MG). A description of the brake equipment together with some details on general maintenance of vacuum brakes in goods and passenger vehicles is therefore included here Fig 4.04 give the schematic diagram of the system as adopted in MG EMUs.
2 When vacuum is created in the train pipe, the ball valve establishes communication between the chamber above the piston and portion of cylinder below the piston. With equal vacuum above and below the piston, the piston comes down by gravity and the brakes are released. When vacuum in the train pipe is reduced by admission of air, the ball valve closes and the pressure of air below the piston moves it up, the piston movement being assisted by the rolling ring. The amount by which the vacuum is reduced in the train pipe determines the braking force.
3. When a cylinder has to be manually released the 'release valve is operated to establish communication between the chamber and the portion of cylinder below the piston. With equal vacuum on both sides of the piston, the piston comes down by gravity and the brakes get released.
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