Brake Pressures

[darwins]

I understand that from an early time, air brake pressures on the Underground was 70 psi for the main reservoir (and main reservoir pipe) and 55 psi for the brake pipe.

A few questions related to this:

(1) With regard to the Southend to Ealing service, did the District locomotives use the above pressures? I am fairly sure that the LTSR would have used 90 psi for the main reservoir and 70 psi for the brake pipe as most main line railways did. Working at different pressures over the District would have involved some bleeding off.

(2) What were typical brake cylinder pressures on trains using the above system? Were these changed as EP braking replaced the original Westinghouse braking from standard stock onwards?

(3) Were there any changes to the above pressures prior to the introduction of the 1973 stock? Does the 1973 and subsequent stock use 10.0 bar in the main reservoir and 7.0 bar in the reservoir pipe as on the main line Network? What are typical brake cylinder pressures?

[towerman]

There were slight variations between stocks but basically it’s 65psi for train line,75 to 90psi for main line.

[Dstock7080]

normal pressure range of pre-1973 stocks is 5.2-6.2 bar (75 - 90 psi), automatically maintained by pressure governor switches, commonly termed compressor governors. In D78 stock (and formerly 1983 tube stock), maximum pressure is fixed at 8 bar (120 psi), 1973 tube stock at 7 bar (105 psi) and post-1986 stocks at 10 bar (150 psi).

[towerman]

Thanks for that Dstock7080,the newest stock I worked on was72Mk2 which still used the 59/62/67 TS settings.

[darwins]

Oct 9, 2022 13:50:04 GMT Dstock7080 said:

 maximum pressure is fixed at 8 bar (120 psi), 1973 tube stock at 7 bar (105 psi) and post-1986 stocks at 10 bar (150 psi).

Thanks for that. Would there be 10 bar in the main line or is there a reducing valve between the Main Reservoirs and the line?

[Dstock7080]

Oct 11, 2022 7:51:09 GMT darwins said:

Would there be 10 bar in the main line or is there a reducing valve between the Main Reservoirs and the line?

Stock after 1972 only have main-line air pipe.

[darwins]

There is a nice system diagram for the A60 stock here - districtdavesforum.co.uk/post/446034/thread

Which makes me want to know if compressors have always been on trailer cars? I am guessing that up to and including Standard Stock they would have been on the motor cars. Again guessing that the move to the trailers makes more room for control equipment (particularly on tube stock) as well as reducing the weight of motor cars.

[Dstock7080]

Oct 11, 2022 11:04:40 GMT darwins said:

Which makes me want to know if compressors have always been on trailer cars? I am guessing that up to and including Standard Stock they would have been on the motor cars. Again guessing that the move to the trailers makes more room for control equipment (particularly on tube stock) as well as reducing the weight of motor cars.

Standard Stock had compressors in the equipment compartment behind the driving cab
1938, 1956/59/62, 1967, 1972, 1973, 1983, 1995, 1996, 2009 Tube Stock compressors under trailer cars
1986, 1992 Tube Stock are all motored cars, so compressors under UNDM cars

O/P/CO/CP compressors under 14xxx/54xxx numbered DM car
R Stock were all motored cars, so compressors under 232xx, 232Axx, 233xx, 235xx numbered UNDM cars
A, C, D Stock compressors under trailer cars
S Stock are all motored cars, so compressors under DM cars