Patent GB-321235-A (GB)
Title: Improvements relating to fluid pressure braking apparatus
IPC: B60T15/04
Filed: 1928-08-07
Abstract: 321,235. Westinghouse Brake & Saxby Signal Co., Ltd., (Westinghouse Air Brake Co.). Aug. 7, 1928. Addition to 214,189. Fluid - pressure. - In train-pipe venting valve mechanism for fluid pressure brakes such as described in the parent Specification adapted upon initiation of the operation, automatically to effect the venting of the train-pipe in two stages, the interval between the commencement of the two stages is dependent upon the length of the train and is independent of the extent of leakage from the trainpipe which may occur during the venting operation. In normal conditions. air from the main reservoir 65 supplied to the valve chamber 22 of a valve device 2 by pipe 66 leaks through a port in the piston 20 and with the magnet valve 3 de-energized and closed the slide valve 23 is held in the position shown, by the spring 21. The train-pipe 15 is thus charged from the main reservoir through the reducing valve 5. the cavity 69 of the valve 23. and passage 71 in the driver's valve 1. The chamber 11 and reservoir 12 of the equalizing valve 10, 17 are also charged from the reservoir through the cavity 73 of the valve 23. If traffic conditions are unfavourable, the magnet valve 3 is de-energized, the piston chamber 19 of the valve 23 is thus vented through the port 25 and the valve 23 is moved to the right cutting off the main reservoir from train-pipe and equalizing chamber 11 and connecting the chamber to the first reduction reservoir 74 by the valve cavity 73 and pipes 13, 75. The equalizing valve 10, 17 is thus raised and the train-pipe vents through a choke-plug 18 until the reduction of pressure corresponds to that effected in the chamber 11. With the valve 23 in its right hand position, also. the main reservoir charges through a reducing valve 6 cavity 91 in the valve 23 and passage 90. the chamber 52 of a valve device D and also through a choked passage 89, 87 the chamber 50 of this valve device and the chamber 47 and reservoir 48 of a hold-back valve device H. The diaphragm 49 of the device D is thus moved to the right to connect the chamber 52 to a timing reservoir 57 through a passage 56 and to close the valve 62. When the discharge valve 17 is unseated, the brake pipe 15 in addition to its connection to atmosphere through the choke plug 18 is connected also to the larger piston chamber 38 of a valve device C and as the lower piston chamber 40 thereof is also connected to the train-pipe the valve moves to the lower position in which the cavity 85 thereof connects the passage 90 to the chamber 47 of the valve H and to the chamber 50 of the valve D. The pressures in the chambers 50 and 52 thus equalize and the diaphragm 49 moves to the left to close the passage 56 and open the valve 62 as shown. With this valve open and the valve C in the lower position, charging of the timing reservoir is continued but at a slower rate than before through the passage 90, valve cavity 85, passage 84, choke 83 and passage 81. With the valve 62 unseated, the timing reservoir 57 is connected by the passage 81 to the lower chamber 44 of the valve H. When the discharge valve 17 seats after the completion of the first stage in the pressure reduction, the valve H returns to the upper position by reason of the venting of the chamber 38 through the port 18 thereby venting the chamber 44 of the valve H and the timing reservoir 57 through the choked atmospheric port 86. When the pressure in the valve chamber 44 falls sufficiently the pressure in the chamber 47 overcomes the spring 45 and the valve H moves to the lower position to connect equalizing valve chamber 11 and the reduction reservoir 74 to the second reduction reservoir 79 by the passages 75, 80 and valve cavity 96. The discharge valve 17 is thus again unseated to effect the second stage of train-pipe pressure reduction. If the driver's valve 1 is not in the lap position, the reduction reservoir 79 is connected to atmosphere through the port 82 so that the train-pipe is thus completely seated at the second stage. The degree of charging of the timing reservoir 57 and thus the interval between the initiation of the two stages of train-pipe pressure reduction is determined bv the time taken for the first stage of reduction of the train-pipe pressure and thus by the length and capacity of the train-pipe. If leakage occurs in the train-pipe during the operation of the device the opening of the discharge valve 17 will be delayed and it will not remain open as long as if there were no leakage, the period during which the timing reservoir is charged at the higher rate through the passage 59 of the valve D will thus be prolonged though the charging at the slower rate is shortened. The degree of charging of the reservoir and thus the interval between the initiation of the two stages of train-pipe venting will thus be substantially constant irrespective of the leakage.