27-11-2012, 04:56 PM
AIR BREAK SYSTEM
INDIAN RAILWAY presentation.pptx (Size: 518.51 KB / Downloads: 29)
Principle of working
The compressed air is used for obtaining brake application. The brake pipe and feed pipe run throughout the length of the coach. Brake pipe and feed pipe on consecutive coaches in the train are coupled to one another by means of respective hose couplings to form a continuous air passage from the locomotive to the rear end of the train. The compressed air is supplied to the brake pipe and feed pipe from the locomotive. The magnitude of braking force increases in steps with the corresponding reduction in brake pipe pressure and vice-versa.
Brake Release
The driver has placed the brake valve in the "Release“ position. Pressure in the brake pipe is rising and enters the triple valve on each car, pushing the slide valve provided inside the triple valve to the left. The movement of the slide valve allows a "feed groove" above it to open between the brake pipe and the auxiliary reservoir, and another connection below it to open between the brake cylinder and an exhaust port. The feed groove allows brake pipe air pressure to enter the auxiliary reservoir and it will recharge it until its pressure is the same as that in the brake pipe. At the same time, the connection at the bottom of the slide valve will allow any air pressure in the brake cylinder to escape through the exhaust port to atmosphere. As the air escapes, the spring in the cylinder will push the piston back and cause the brake blocks to be removed from contact with the wheels. The train brakes are now released and the auxiliary reservoirs are being replenished ready for another brake application.
Brake Application
The driver has placed the brake valve in the "Application" position. This causes air pressure in the brake pipe to escape. The loss of pressure is detected by the slide valve in the triple valve. Because the pressure on one side (the brake pipe side) of the valve has fallen, the auxiliary reservoir pressure on the other side has pushed the valve (towards the right) so that the feed groove over the valve is closed. The connection between the brake cylinder and the exhaust underneath the slide valve has also been closed. At the same time a connection between the auxiliary reservoir and the brake cylinder has been opened. Auxiliary reservoir air now feeds through into the brake cylinder. The air pressure forces the piston to move against the spring pressure and causes the brake blocks to be applied to the wheels. Air will continue to pass from the auxiliary reservoir to the brake cylinder until the pressure in both is equal. This is the maximum pressure the brake cylinder will obtain and is equivalent to a full application. To get a full application with a reasonable volume of air, the volume of the brake cylinder is usually about 40% of that of the auxiliary reservoir.
Lap
When the driver places the brake valve in the "Lap" position while air is escaping from the brake pipe, the escape is suspended. The brake pipe pressure stops falling. In each triple valve, the suspension of this loss of brake pipe pressure is detected by the slide valve because the auxiliary pressure on the opposite side continues to fall while the brake pipe pressure stops falling. The slide valve therefore moves towards the auxiliary reservoir until the connection to the brake cylinder is closed off. The slide valve is now half-way between its application and release positions and the air pressures are now is a state of balance between the auxiliary reservoir and the brake pipe. The brake cylinder is held constant while the port connection in the triple valve remains closed. The brake is "lapped".
Lap does not work after a release has been initiated. Once the brake valve has been placed in the "Release" position, the slide valves will all be moved to enable the recharge of the auxiliary reservoirs. Another application should not be made until sufficient time has been allowed for this recharge. The length of time will depend on the amount of air used for the previous application and the length of the train.