The Next Generation
Following on from the original EP stock, the system was developed further on the second generation of Multiple Unit trains built for British Rail in the 1970s such as the Class 313 EMU. The Westinghouse air system was abandoned in favour of a fully electrical system of control, so that the need for a brake pipe and triple-valves was dispensed with. Instead a single air pipe, now called the Main Reservoir Pipe ran the length of the train. It operated at 10 bar and in addition to feeding each brake cylinder reservoir also provided air for the secondary suspension systems (air bags) and power doors which were being introduced.
Each brake reservoir stored air at a pressure of 7 bar and was fed via a pressure reducing valve off the Main Reservoir Pipe. The driver's brake handle passed control voltages down three wires to each EP control valve, which allowed air from the brake reservoir to pass into the brake cylinder, thereby activating the disc brake. The presence of the voltage held the brakes off, providing a Fail Safe system.
The 3 step "Westcode" brake uses three wires and these operate in a binary sequence to control the brake step. 10 & 11 are the brake coding to provide the 3 steps, 12 wire is emergency brake, 15 wire is EP brake negative.
Positions on the brake handle are:
- Release - Trainwires 10,11 and 12 energised
- Step 1 - Trainwire 10 de-energised, 11 energised, 12 energised
- Step 2 - Trainwire 10 energised, 11 de-energised, 12 energised
- Step 3 - Trainwire 10 de-energised, 11 de-energised, 12 energised.
- Emergency - All three Trainwires de-energised and earthed
Read more about this topic: Electro-pneumatic Brake System On British Railway Trains
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