AIR BRAKE SYSTEM

INTRODUCTION Air Brake System is used for operating the brake system, actuated by compressed air. Modern trains rely upon a fail preventive air brake system that is based upon a design patented by George Westinghouse on March 5,1872. In the air brake's simplest form, called straight air system, compressed air pushes on a piston in a cylinder. The piston is connected through mechanical linkage to brake shoes that can rub on the train wheels, using the resulting friction to slow the train.

OPERATION The locomotive compressor charges the feed pipe and the brake pipes through out the length of the train. The feed pipe is connected to the brake cylinder through the distributor valve. Brake application takes place by dropping the pressure in the brake pipe.

In air brake system we first charge the train system with compressed air to certain predetermined level of air pressure through two pipes named feed pipes and brake pipes. The feed and brake pipes are charged to a pressure of 6.0 and 5.0 kg/sq.cm respectively. When brakes are to be applied the air pressure in brake pipe is reduced by the driver which actuates the distributor valve fitted under every wagon or coach on the train .The distributor valve supplies the compressed air from auxiliary reservoir to one side of the piston in the brake cylinder pushing out the piston rod and applying the brakes .The guard and the passengers can also apply the brakes in case of an emergency .During train partings and accidents brakes also apply automatically and with higher force than that of vacuum brakes .When the air pressure in brake pipe is restored to the normal pressure ,the brakes are released. The brakes can also be manually released after the engine has been detached .After application of brakes in air brake system the brakes remain in on position for hours together. Only those engines which are fitted with the air brake system can only work such trains .Such wagons/coaches can also not be worked with other trains with vacuum brake system.

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SYSTEM OF AIR BRAKE TWIN PIPE SYSTEM:As already stated above each and every brake system has two air pipes from one end to the other end lengthwise. One pipe is used to continuously charge/feed the compressed air to the auxiliary reservoir and is called as Feed pipe .The second pipe is used for application and releasing of brakes and is termed as Brake pipe .As such this system is called as Twin pipe system. This system has the following merits:Feed pipe charges the Auxiliary reservoir continuously and maintains the predetermined air pressure in A.R(Auxiliary reservoir).On application of brakes the A.RS compressed air is fed to the brake cylinder and there is a certain fall in air pressure in A.R due to the same .But the feed pipe immediately/simultaneously charges the A.R and maintains the desired air pressure in A.R .Any number of brake applications releasing may be done by the driver in quick succession, the air

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pressure in A.R will remain the same i.e.; there will be no decrease in the air pressure of A.R. This feature is not possible in case feed pipe is removed/isolated from the Air brake system, because the brake pipe will have to shoulder the burden of feed pipe in addition to his own job. In such an event the charging of A.R will take more time to be ready for subsequent brake applications .Resultantly the application of brakes in quick succession is not possible. In case due to any reason one pipe of a coach or any wagon gets damaged or goes defective ,it can be bypassed in twin pipe system and the detachment of the coach or wagon would not be essential as in the case of single pipe system ,But in this case the train will be worked as single pipe system.

SINGLE PIPE SYSTEM:In this system there is provision of only one air pipe from one end of a wagon/coach to the other end instead of two pipes .This pipe is called as brake pipe .This brake pipe singularly charges the auxiliary reservoir and also applies and releases the brakes .In this system the driver feels very easy in maintaining/charging the brake pipe only but this is not so advantageous to that of Twin pipe system .In this system the auxiliary reservoir is not charged while the A.R supplies air to brake cylinder. As such brakes in quick succession cannot be applied and released .In case of any damage or defect in the air brake system of any coach/wagon ,there is no alternative than to detach such coach/wagon from train en route .In this system after emergency application of brakes the driver shall have to wait for some time to fully release the train before restarting other wise some danger to the train has to be faced. Therefore, the administration has adopted Twin pipe air brake system on the railways .The train examination staff must ensure4

that all trains examined by them are invariably having Twin pipe air brake system .In case a train terminates at their station with single pipe system they must thoroughly check and investigate the reasons for single pipe system and ensure necessary repairs to put the defective coach/wagon back to Twin pipe system.

TYPES OF AIR BRAKESThere are two types of air brakes which are present, they are, 1 .Direct release system 2 .Graduated release system

DIRECT RELEASE SYSTEM:In this system when after application of brakes ,the brakes are released ,the air of the brake cylinder does not quickly go to the atmosphere through the distributor valve .Instead it goes slowly .The Distributor valve is not provided with such a feature which may permit the air of brake cylinder to escape quickly and release the piston quickly .Second or subsequent application of brake is not possible until and unless the brake cylinder air is completely exhausted .It is not possible for the distributor valve to make the releasing movement of piston to abruptly change to applying position .As such the application and release of brakes in quick succession cannot be achieved at all .So this system is termed as Direct release system.

GRADUATED RELEASE SYSTEM:In this system application and release of brakes in quick succession is feasible in any number of times .In this system the

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movement of piston from application to release and vice versa can be changed with decrease and increase of air pressure in B.P .In this case there is no need for completely discharging the air pressure of brake cylinder .The distributor valve fitted in this type ,has the special feature which actuates the brake cylinder piston with the decrease and increase in B.P ,pressure to the tune of 0.5 kg/cm^2 or above. At the time of speed restrictions or while negotiating down gradients it has become very easy to control the speed of the train to the will of driver .It is due to this reason that this system is called Graduated release system.. From the above,one can easily understand that the type of air brake system in use on our railway system is Twin pipe graduated release air brake system .But we call it only air brake system in short which has the same meaning and nothing else as in the case of vacuum where partial vacuum is used but termed as vacuum only.

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PRINCIPLE OF OPERATION OF TWIN PIPE GRADUATED RELEASE AIR BRAKE SYSTEM :A. Charging the brake system > Brake pipe throughout the length of train is charged with compressed air at 5 Kg/cm2. > Feed pipe throughout the length of train is charged with compressed air at 6 Kg/cm2.

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> Control reservoir is charged to 5 Kg/cm2 . > Auxiliary reservoir is charged to 5 Kg/cm2. B. Brake application stage > For brake application the brake pipe pressure is dropped by venting air from the drivers brake vale. Subsequently the following action take place. > The control reservoir is disconnected from the brake pipe. > The distributor valve connects the auxiliary reservoir to the brake piston is pushed out wards for application of brakes. > The auxiliary reservoir is however continuously charged from feed pipe at 6 Kg/cm2. Description Minimum Brake Application Service Brake Application Full Service Brake Application Reduction in B. P. Pressure 0.5 to 0.8 Kg/cm2 1.0 to 1.0 Kg/cm2 Brake pipe is fully exhausted and its pressure reduces to almost zero. C. Brake release stage > Brakes are released by recharging brake pipes to 5 Kg/cm2 pressure through the driver s brake valve. > The distributor valve isolates the brake cylinder from the auxiliary reservoirs.

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> The brake cylinder pressure is vented to atmosphere through DV and the Brake cylinder piston moves inwards.

AIR BRAKE EQUIPMENTIn addition to the compressor, governor, reservoirs, and valves previously mentioned, all airbrake systems have many other parts. Typical examples are the cutout cocks; pressure gages; equalizing reservoir; distributing, feed, reducing, and quick release valves; and deadman control. These are discussed in the following subparagraphs. A. Cutout cocks are used to bypass parts of the circuit when they are not needed. B. Two pressure gages are common in airbrake systems. One indicates main air reservoir and equalizing reservoir pressures; the other shows locomotive brake cylinder and brake pipe pressures. C. An equalizing reservoir adds volume to the space above the equalizing piston in the brake valve so that reductions in brake pipe pressure may be properly made during service applications of the brakes. D. The distributing valve, when actuated by the brake valves, permits air to flow to the locomotive brake cylinders, maintains pressure against leakage when brakes are held in applied position, or permits air to exhaust to the atmosphere when brakes are released.

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E. A feed valve automatically maintains a predetermined air pressure in the brake pipe. F. A reducing valve reduces main reservoir pressure for independent airbrake operation or for an air signal system. G. A quick release valve provides a rapid release of brake cylinder pressure during the release operation. H. Deadman control is a safety device which must be pressed when the locomotive is in operation. It is released only when the brakes are to be applied. Release of the deadman pedal causes a warning whistle to sound for approximately 4 seconds after10

which the brakes are automatically applied; automatic application of the brakes can be avoided if the pedal is pressed again during the warning period.

28LAV-1 AND IRAB SYSTEMDiesel locomotives of Indian Railways are equipped with brake system equipped with 28LAV-1 Brake system for use both in vacuum and air braked Trains or IRAB-1 brake system. Air brake system consists of a no. of valves for proper operation of system .These valves must be tested after their overhauling before fitment on locos. Tested valves ensure reliability of Air brake system & hence safe & reliable operation of locomotives inline. Air Brake valve Testing bench ensure fitment of tested valve in system thus ensuring reliability of loco movement. Diesel locomotives of Indian Railways are equipped with brake system designed by either M/S WABCO/ USA or M/S KNORR Germany or IRAB-1 Indian Railways or M/S KNORR Brake (NYAB). Initially locomotives were equipped with M/S WABCO, USA designed 28LV-1 Brake system for use in vacuum brake train only. In 80's locomotives were switched over to 28LAV-1 Brake system for use both in vacuum and air braked Trains. Now most of the locomotives are equipped with IRAB-1 brake system, which are suitable for only air-braked trains.

28-LAV-1 BRAKE Locomotives.

EQUIPMENT

for

Diesel-Electric

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28-LAV-1 BRAKE EQUIPMENT The combined compressed air brake and vacuum brake equipment described in this pamphlet is for diesel-electric locomotives in single or multiple unit service which are to move vacuum braked trains or pressure braked trains of either the direct or graduated release type. The locomotive brake sare operated by compressed air, either independently or in conjunction with the car brakes. When the car brakes are of the vacuum type, they are piloted by the air system. The important features of the 28-LAV-1 Brake Equipment described in this pamphlet are as follow: 1. Locomotive brakes may be applied with any desired pressure between the minimum and maximum. This pressure will be automatically maintained in the locomotive brake cylinders within maximum specified leakage from them and regardless of variation in piston travel until released by the brake valve. 2. The locomotive brakes can be graduated on and off with either the automatic or the independent brake valves; however, when operating car equipment of the direct release type pressure brake, the car brakes cannot be graduated off. Therefore, it is very important to set the brake valve cut out control knob for the type of train to be handled. 3. It is always possible to release the locomotive brakes with the independent brake valve, even when automatically applied. 4. Fast development of maximum braking force in emergency. 5. Multiple unit operation.

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FUNDAMENTAL OPERATION This section of the pamphlet describes the fundamental operation of the combined devices of the 28-LAV-1 Brake Equipment as found in this installation. A detailed description of the functions of each device is given in the Description and Operation of the Devices section of this pamphlet. A piping diagram which contains all of the details of the Wabtec supplied equipment in this installation is included at the end of this pamphlet. When operating, the compressor portion of the compressor/exhauster supplies compressed air through the main reservoir system to the 30R-CDW Brake Valves and Manual PushButton Valves at each control station and also to the 28LUAV-1 Brake Equipment Rack located in the machinery room of the locomotive. The 28-LUAV-1 Brake equipment rack includes such important items as the 30-CW Module, N-1 Reducing Valves, HS-4 Control air Valve, MU-2B Valve, J-1 Relay Valve, 28-VB Control Valve, etc. In a similar manner, the exhauster portion of the Compressor/Exhauster provides vacuum directly to the VA-1-B Control Valve and VA-1 Release Valves. TYPES OF 28-LAV-1 VALVES USED IN LOCOMOTIVES:A-9 Valve The A-9 Automatic Brake Valve is a compact self lapping, pressure maintaining Brake Valve which is capable of graduating the application or release of locomotive and train brakes. A-9 Automatic Brake Valve has five positions: Release, minimum Reduction, Full Service, Over Reduction and Emergency.

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SA-9 Valve SA-9 Independent Brake Valve is a compact self lapping, pressure maintaining Brake Valve which is capable of graduating the application or release of Locomotive Air Brakes independent of Automatic Brake. The SA-9 Independent Brake Valve is also capable of releasing an automatic brake application on the Locomotive without affecting the train brake application. The SA9 Brake Valve has three positions : quick release, release and application. MU 2B VALVE The MU-2B Valve is a manually operated, two positions and multiple operated valve arranged with a pipe bracket and is normally used for locomotive brake equipment for multiple unit service between locomotives equipped with similar system in conjunction with F-1 Selector Valve. D-1 Emergency Brake Valve The D-1 Emergency Brake Valve is a manually operated device

Which provides a means of initiating an emergency brake application.

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FUNCTION OF AIR COMPRESSORThe air compressor of the locomotive stores the air in its main reservoir at a pressure of 8-10 kg/cm^2 and it is supplied to the system charging the feed pipes and brake pipes commonly called as FP and BP at a pressure of 6kg/cm^2 and 5kg/cm^2 respectively. Auxiliary reservoir is charged by the feed pipe through the check valve and isolating cock. The auxiliary reservoir is also charged by the brake pipe through distributor valve in case the feed pipe is unable to charge, or has been

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eliminated. For continuity of air pressure through out the rake ,the cut off angle cocks of the brake and the feed pipe and isolating cocks should be kept open. The cut off angle cocks on the last coach of the rake and front cut off angle cocks of the locomotive should be kept closed.

VALVES OVERHAUL PROCEDURE The compressor must first be electrically isolated with the fuses removed and an electrical isolation and work permit granted by the chief engineer. Thereafter the first stage and the second stage suction and discharge valves should be removed and brought to the workshop for overhauling. Marine compressors use the HOERBIGER automatic valves. The suction and the discharge valves look similar; however the direction of the operation and the spring stiffness differs. The suction valve springs are of lower spring stiffness than the discharge ones and they must never be mixed up. Also when using new spare parts the part number must be carefully

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checked from the operation and maintenance manual to avoid mixing them up. When opened up the suction valves are found to be in clean condition while the discharge valves would have some degree of carbonization. In case a valve is opened up and some parts are found to be broken, all the broken parts must be located to avoid any further damage to the machine. An exploded view of the compressor valve has been shown and the overhaul procedure is as follows: 1. Remove the split pin and open the castle nut. 2. Dismantle all the parts and soak in kerosene or clean diesel oil. 3. Clean all the parts with a soft brush. In case of a hard deposit a copper plate of washer can be used for the scraping action. 4. Check the valve plates and the valve seats for any damage and cracks. If any signs of fatigue cracks on the valve plates are present, then the valve plate must be replaced with new ones. The valve plate must never be turned over and used as it can lead to fatigue failure. 5. The valve plate and the valve seat must be separately lapped on a surface plate using fine and extra fine grinding paste. 6. Thereafter all the parts must be washed with diesel and cleaned with compressed air. 7. The valve should then be assembled, with the lapped surface of the valve plate and the valve seat facing each other. 8. After the assembly of the valve the operation of the valve should be checked by a soft wooden stick. After the overhaul the valves have to be checked for leakage. The space above the valve plate should be filled up with water or light oil like kerosene. If after a few minutes no drop in level or17

leakage is there then the valve is satisfactory for the use. While installing care should be taken to avoid the interchange of the suction and the discharge valves, as it could lead to an explosion due to over pressurization of the compression chamber.

BRAKE BINDINGBrake binding is defined as the situation when the brake block is in contact with the wheel tread though the A-9 valve position is in released position. The severity of the brake binding depends on the force exerted by the brake blocks on the wheel tread. CONFUSION IN BRAKE BINDING Very often wheel skidding is wrongly interpreted as brake binding. Though brake application quality in relation with the adhesion is the basic cause of wheel skidding, the incidence of wheel skidding must not be merged with the incidence of brake binding. CAUSES OF BRAKE BINDING > DEFECTS IN LOCOMOTIVE > DEFECTS IN TRAIN HANDLING > DEFECTS IN DISTRIBUTOR VALVE > DEFECTS IN BRAKE CYLINDER > DEFECTS IN DIRT COLLECTOR > DEFECTS IN SAB BRAKE REGULATOR > DEFECTS IN BRAKE GEAR18

Released position

BP BP

CR

AR

BC

ATM

Application position

AR BP CR BC ATM

REFERENCE Internet

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