Electro-pneumatic brake system on British railway trains

The Electro-pneumatic brake system on British railway trains was introduced in 1950 and remains the primary braking system for multiple units in service today. The Southern Region of British Railways operated a self-contained fleet of electric multiple units for suburban and middle distance passenger trains. From 1950, an expansion of the fleet was undertaken and the new build adopted a braking system that was novel in the UK, the electro-pneumatic brake in which compressed air brake operation was controlled electrically by the driver. This was a considerable and successful technical advance, enabling a quicker and more sensitive response to the driver’s operation of brake controls.

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:

The first Southern units fitted with EP brake could be considered the Bulleid double deck 4-DDs built 1949 (4001 & 4002). The EP brake fitted to this stock was not of the self lapping type and still required the Westinghouse brake as the 'fail to safe' braking as the EP brake fitted was of the 'energise to apply' type, which meant if there was a loss of brake control voltage the EP brake was inoperative. The 4-DDs were based on the earlier 4-SUB but were not operationally compatible with either the 4-SUB or later EPB stock.

Starting in 1950, a large new fleet of suburban multiple units was delivered to a pre-war design and, as well as other technical improvements, they were equipped with the electro-pneumatic brake – universally referred to as "the EP brake". The advance in braking technology dominated the other developments and the designation of the train units was 2-EPB and 4-EPB for the two- and four-car units respectively. The design was successful and a larger fleet of broadly similar design was built and the Kent Coast Line electrification extended the adoption of the EP brake to medium distance passenger operation but still confined to multiple units. (A small fleet of locomotives were built for the Southern Region and had a brake control system fitted that was compatible for interoperability purposes.)

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