Origins
From the 1920s, the Southern Railway of the UK and its predecessor companies had adopted electrification and multiple-unit train operation as a solution for dense and intensive passenger service requirements. The fleet prior to World War II used the two-pipe Westinghouse Air Brake system, which was more effective than the generally prevailing vacuum brake then in favour in the UK. However it had disadvantages, chiefly:
- Partial release of a Westinghouse brake application was unresponsive and usually required a full release – which took a considerable time – and then a re-application.
- On a long train the brake force during a brake application was not consistent along the length of the train; the response to the driver’s operation of the brake valve varied according to train length and the variation caused longitudinal surging.
- Release after a full application is slow.
- Response to the driver’s operation of the brake valve was inconsistent and not self-lapping (that is, the position of the brake control valve set the rate of change of brake force, not the level of the brake force).
Read more about this topic: Electro-pneumatic Brake System On British Railway Trains
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