Electro-pneumatic brake system on British railway trains
Encyclopedia
The Electro-pneumatic brake system on British railway trains was introduced in 1950. The Southern Region of British Railways
operated an intensive self-contained fleet of electric multiple unit
s 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.
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:
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.)
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.
The electrical control system required control cables throughout the length of the train (in addition to the two air pipes for Westinghouse operation) and a jumper cable was provided at each end of every unit for use when two or more units were coupled to run in multiple. In 1950, no electronic control was possible and the system used four conductors in the cable to achieve graduated braking rates.
The EP brake system was greatly appreciated by drivers and was adopted for subsequent builds of rolling stock on the Southern Region of British Railways
, including middle-distance passenger stock.
The brake reservoirs store air at a pressure of 7 bar and are fed via a pressure reducing valve off the Main Reservoir Pipe. The driver's brake handle passes control voltages down three wires to each EP control valve, which allows air from the reservoir to pass into the brake cylinder, thereby activating the disc brake. The presence of the voltage holds the brakes off, providing a Fail Safe system.
Positions on the brake handle are:
Southern Region of British Railways
The Southern Region was a region of British Railways from 1948. The region ceased to be an operating unit in its own right in the 1980s and was wound up at the end of 1992. The region covered south London, southern England and the south coast, including the busy commuter belt areas of Kent, Sussex...
operated an intensive self-contained fleet of electric multiple unit
Electric multiple unit
An electric multiple unit or EMU is a multiple unit train consisting of self-propelled carriages, using electricity as the motive power. An EMU requires no separate locomotive, as electric traction motors are incorporated within one or a number of the carriages...
s 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.
Origins
From the 1920s, the Southern RailwaySouthern Railway (Great Britain)
The Southern Railway was a British railway company established in the 1923 Grouping. It linked London with the Channel ports, South West England, South coast resorts and Kent...
of the UK and its predecessor companies had adopted electrification
Railway electrification system
A railway electrification system supplies electrical energy to railway locomotives and multiple units as well as trams so that they can operate without having an on-board prime mover. There are several different electrification systems in use throughout the world...
and multiple-unit train operation as a solution for dense and intensive passenger service requirements. The fleet prior to World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
used the two-pipe Westinghouse Air Brake
Air brake (rail)
An air brake is a conveyance braking system actuated by compressed air. Modern trains rely upon a fail-safe air brake system that is based upon a design patented by George Westinghouse on March 5, 1872. The Westinghouse Air Brake Company was subsequently organized to manufacture and sell...
system, which was more effective than the generally prevailing vacuum brake
Vacuum brake
The vacuum brake is a braking system employed on trains and introduced in the mid-1860s. A variant, the automatic vacuum brake system, became almost universal in British train equipment and in those countries influenced by British practice. Vacuum brakes also enjoyed a brief period of adoption in...
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).
The First EP-fitted units
The first Southern units fitted with EP brake could be considered the Bullied 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. 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
British Rail Class 416
British Rail Class 416 electric multiple units were built between 1953 and 1956. They were intended for inner suburban passenger services on London's Southern Electric network...
and 4-EPB
British Rail Class 415
British Rail Class 415 was a suburban 750 V DC third rail electric multiple unit commissioned by the Southern Region of British Railways. Built between 1951 and 1957, it became the most numerous class on the region after the withdrawal of the 4Subs...
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
Kent Coast Line
The Kent Coast Line is railway line that runs from Dover Priory to Margate in the English county of Kent.It was electrified by BR under the 1955 Modernisation Plan.- Services :...
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.)
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.
Advantages and Developments
The advantages of the EP system are that:- The driver’s brake valve is self-lapping; the position of the valve activates a specific brake pressure in the brake cylinders and therefore a specific braking rate.
- The distributors are activated instantly and simultaneously, so that there is no longitudinal surging and the response is consistent irrespective of train length.
- Release of a brake application starts instantly in response to the driver’s brake valve, throughout the train; and partial release and re-application is possible.
The electrical control system required control cables throughout the length of the train (in addition to the two air pipes for Westinghouse operation) and a jumper cable was provided at each end of every unit for use when two or more units were coupled to run in multiple. In 1950, no electronic control was possible and the system used four conductors in the cable to achieve graduated braking rates.
The EP brake system was greatly appreciated by drivers and was adopted for subsequent builds of rolling stock on the Southern Region of British Railways
Southern Region of British Railways
The Southern Region was a region of British Railways from 1948. The region ceased to be an operating unit in its own right in the 1980s and was wound up at the end of 1992. The region covered south London, southern England and the south coast, including the busy commuter belt areas of Kent, Sussex...
, including middle-distance passenger stock.
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 brake pipe was discarded, and just one pipe, called the Main Reservoir Pipe runs the length of the train. It operates at 10 bar and in addition to feeding each brake cylinder reservoir also provides air for the secondary suspension systems (air bags) and power doors which were introduced.The brake reservoirs store air at a pressure of 7 bar and are fed via a pressure reducing valve off the Main Reservoir Pipe. The driver's brake handle passes control voltages down three wires to each EP control valve, which allows air from the reservoir to pass into the brake cylinder, thereby activating the disc brake. The presence of the voltage holds the brakes off, providing a Fail Safe system.
Positions on the brake handle are:
- Release - Trainwires 10,11 and 12 energised
- Step 1 - Trainwire 10 de-energised
- Step 2 - Trainwire 11 de-energised
- Step 3 - Trainwire 12 de-energised
- Emergency - All three Trainwires de-energised and earthed
Brake Continuity Wire
On the previous EP brake systems, if the train divided or a serious air leak occured the brakes would automatically apply. This feature was lost with the removal of the Brake Pipe, so an electronic equivalent was created. The Brake Continuity wire (a.k.a. Trainwire 13) is fed with a 120v DC control voltage from the battery and runs in a loop round the train, passing through various Governors (air pressure operated electrical switches) in each carriage, finally feeding the power and brake control handle(s) in the driver's desk. If any of the Governors should open due to low air pressure, the control voltage will be cut off and this will shut off traction power to the motors and apply the Emergency brake.Further reading
- Moody G T, Southern Electric 1909-1979, 1979, Ian Allan Ltd, ISBN 0-7110-0924-4
- "Electro-pneumatic brakes" on Railway Technical Web Pages gives a world view in context at http://www.railway-technical.com/ep-brakes.shtml