Patent GB-269503-A (GB)
Title: Improvements relating to fluid pressure braking apparatus
IPC: B60T15/04
Filed: 1927-03-17
Abstract: 269,503. Westinghouse Brake &. Saxby Signal Co., (Assignees of Farmer, C. C.). April 15, 1926, [Convention date]. Fluid-pressure. - Automatic compressed air brake systems are provided with a valve de. vice adapted to cut off the supply of compressed air to the train-pipe upon an emergency reduction of train-pipe pressure effected other than by the operation of the driver's valve, whereby unintentional release of the brakes is prevented. The apparatus may include a trainpipe vent valve device operated by the reduction of train-pipe pressure and adapted to control the operation of the cut-off valve. The apparatus shown comprises a cut-off valve device 4, operated by fluid-pressure controlled by a valve device 3 operated by fluid-pressure controlled by a valve device 2 which is operated by a sudden reduction of train-pipe pressure and serves also to vent the train-pipe to atmosphere. The vent valve device 2 comprises a piston 33 which actuates a slide valve 35 controlling a pressure fluid supply for operating a piston 36 which actuates the train-pipe vent valve 38. Under running conditions air is supplied from the train-pipe 12 by the passages 41, 42 and the valve chamber 39 to the piston chamber 32 and by the passage 43 to the slide valve chamber 34. The fluid pressures on the two sides of the piston 33 being thus equalized, it is held with the slide valve 35 in the position shown by a spring 44. Also since the chamber 37 of the piston 36 is vented to atmosphere through the restricted port 47, the valve 38 is seated by the train-pipe pressure acting thereon. The chamber 23 of the control valve device 3 is normally maintained at atmospheric pressure by the port 48 and the chamber 28 is supplied with compressed air from the main reservoir 56 through the feed valve 31 and pipe 30 so that the slide valve 29 assumes the position shown in which the chamber 17 of the cutoff valve device 4 is open to atmosphere by the pipe 18 and passage 50. The valve device 4 is therefore maintained in the open position shown in which the driver's valve 6 in the running position, air from the main reservoir 56 is supplied to the train-pipe 12 through the usual feed valve device 31, passages 51, 52, 20, 22. If a sudden reduction of train-pipe pressure is effected, the piston 33 of the vent valve device 2 moves upwardly and the slide valve 35 connects a passage 45 to the valve chamber 34, whereby pressure fluid is supplied to the piston chamber 37, causing the unseating of the valve 38 and the consequent venting of the train-pipe by way of the chamber 39 and passage 46. The pressure fluid supplied to the piston chamber 37 also flows to the piston chamber 23 of the valve device 3, causing the slide valve 29 to connect the chamber 17 of the cut-off valve 4 to the main reservoir 56 by the pipes 55, 18. The piston 14 of the valve 4 thus moves to the left. thereby closing the passage 22 to the passage 20 and thus cutting off the supply of pressure fluid to the trainpipe 12. The valve 29 in its operated position also connects the main reservoir pipe 55 to the valve chamber 23 so as to maintain the valve in this position. In order to return the valve 29 after an operation, a cock 57 is temporarily closed to cut off the valve chamber 23 from the main reservoir and permit it to vent to atmosphere. The return of the valve 29 effects the return of the cut-off valve to the open position.