Working principle of Air Brake :
Under normal conditions, the Brake pipe is charged with 5 kg/Cm2 from the Loco. The control reservoir and the Auxiliary reservoir are also charged with 5 kg/Cm2 from BP through Distributor valve in case of the single pipe system. In twin pipe system the auxiliary reservoir is charged to 6 kg/Cm2 through feed pipe.
When the brake pipe is 5 kg/Cm2, the brake cylinder is connected to exhaust through distributor valve in order to keep the brakes in the released position fully. Whenever the brake pipe pressure is reduced below the CR pressure, the DV connects the auxiliary reservoir with the brake cylinder and the air from AR
is sent into the brake cylinder to apply the brake. Whenever the brake pipe pressure is equal to CR pressure, the DV disconnects the BC from AR, and in turn, connects the BC with Exhaust for the release of brakes fully.
Processes involved in working of Air brake system:
- Manual Release
Charging of Air brake system:
Brake pipe is charged with 5 Kg/Cm2 by the driver’s brake valve from the Loco. Feed pipe is charged with 6 Kg/Cm2. AR is charged with 6 Kg/Cm2. (Up to 5 Kg/ Cm2 it is charged by both brake pipe and feed pipe. Beyond 5 Kg/Cm2 & up to 6 Kg/Cm2, it is exclusively charged by feed pipe.) The CR is charged through the distributor valve to 5 Kg/sq cm from BP. During charging Brake cylinder is connected to exhaust through distributor valve, to keep the brakes in the released condition.
Application of brake in Air brake system:
For application, the brake pipe is reduced in steps as given below.
Stages BP pressure is reduced by
- Minimum Reduction 0.5 to 0.8 Kg/Cm2.
- Service application 0.8 to 1 Kg/Cm2.
- Full-service application 1 to 1.5 Kg/Cm2.
- Emergency application Above 1.5 Kg/Cm2.
When the brake pipe pressure is reduced in steps, as shown above, the air from AR is sent into BC to a maximum pressure of 3.8 Kg/ Cm2, during full-service application as well as emergency application. During minimum reduction and service application, the admission of air from AR into BC is directly proportional to the reduction in the BP pressure.
Before AR is connected to BC, the AR and CR are disconnected from BP, and BC also is disconnected from Exhaust. The AR is continuously charged to 6 Kg/Cm2 during brake application by Feed pipe. The CR pressure should remain at 5 Kg/Cm2. However, there may be a little drop in CR pressure during brake application, due to the design.
Releasing/Recharging of Air brake system:
During the release, the BP pressure is increased in steps. When the BP pressure is increased in steps, the brake cylinder is disconnected from AR and in turn connected to exhaust. The air from Brake cylinder is released/vented progressively depending upon the increase in the brake pipe pressure. When the brake pipe pressure is brought to 5 Kg/Cm2 the air from brake cylinder is completely exhausted and the brakes are released fully.
Whenever the loco is detached, BP pressure is brought to zero and brake application takes place due to the existence of CR pressure at the bottom of the main diaphragm. To release the brakes manually, the hollow stem in the DV should be brought to the normal position by releasing the air from CR. To facilitate this, the release valve provided at the bottom of the DV is given a brief pull. During this operation, the air from CR is released which in turn brings the hollow stem to the normal position to connect BC with exhaust for releasing of brakes.