Electro-pneumatic Brake System On British Railway Trains - Westinghouse and EP Brake Operation

Westinghouse and EP Brake Operation

The trains had Westinghouse brake equipment and had an electric control system, activating the compressed air brakes on each coach. In normal operation, the driver used the EP system exclusively but it was not fail-safe. If the electrical system failed, the driver merely had to move the brake valve to a further position and the same valve operated the fail-safe Westinghouse system on the train. This was only done in case of failure or emergency.

The Westinghouse system uses air reservoirs on each vehicle and compressed air is released from these reservoirs to the brake cylinders as the pressure in the train pipe is reduced by the driver operating the brake valve. This process causes a mechanical linkage to press the brake blocks against the wheels.

The release of compressed air into the brake cylinders is achieved by triple valves, which are themselves controlled by the pressure of air in the train pipe, a pneumatic pipe running the length of the train. When the driver wishes to make a brake application, he operates the driver’s brake valve which releases some air from the train pipe, so operating the triple valves. When the driver wishes to release the brakes, his operation of the driver’s brake valve returns compressed air (stored in a cylinder near the driving position) into the train pipe and this moves the triple valve so as to release the air in the brake cylinders to atmosphere, allowing the brake blocks to move clear of the wheels. Although, in multiple-unit operation, the air reservoirs on the vehicles can be relatively quickly charged, the restoration of pressure to the train pipe takes some time as air has to travel physically down the length of the train.

In EP operation, a distributor, performing functions similar to those of the triple valve, is operated directly and instantly by electrical control from the driver’s brake valve. The Westinghouse brake cylinders and air reservoirs and pumps are used, so that only the means of transmitting the driver’s command is changed.