Patent GB-214189-A (GB)
Title: Improvements relating to fluid pressure braking apparatus
IPC: B60T8/32
Filed: 1923-08-13
Abstract: 214,189. Westinghouse Brake & Saxby Signal Co., (Assignees of Thomas, T. H.). April 9, 1923, [Convention date]. Fluid-pressure.-Venting-valve apparatus for effecting the application of fluid-pressure brakes is adapted when the venting operation is initiated, to effect automatically a light initial reduction of train-pipe pressure followed by a second and heavier reduction. The apparatus shown is suitable for use with automatic train speed control equipment but the device may also be embodied in the orm of a driver's valve. It comprises a main valve 4 which when actuated connects the reservoir 12 of a train-pipe equalizing discharge-valve mechanism 10 to a reduction reservoir 34 so as to effect the initial train-pipe pressure reduction and a hold-back valve mechanism 28 controlled by a pilot valve mechanism 17 which serves to connect the equalizing reservoir 12 to a second reduction reservoir 32 after the initial train-pipe pressure reduction has been completed thereby effecting the second pressure reduction. The pilot valve mechanism comprises a valve 24 carried by a piston 21 which can slide against the action of a spring 23 in a hollow piston 17, the piston 21 being provided with a slot through which passes a pin 22 secured to the piston 17. Under running conditions the pipe 57 is closed and air from the main reservoir 7 supplied to the chamber 5 of the valve 4 equalizes through the port 40 in the piston 3 to the chamber 2 so that the valve is held in the position shown by the spring 41, in which it makes the following connections, viz. :-the train-pipe 14 to the equalizing reservoir 12 and chamber 10 by passage 42, valve cavity 44 and passages 45, 11; the reduction reservoirs 32, 34 to exhaust by passages 46, valve cavity 47, and port 58; the chamber 18 of piston 17 and timing reservoir 20 to exhaust by passage 19, cavity 47, and port 58. The chamber 50 of the piston 17 being also open to exhaust by the port 26 this piston is held in the position snown by the spring 52 in which the valve 24 is open thereby rendering the chamber 38 of the piston 28 open to exhaust by passage 59 and as the valve face 29 of this piston is also open to exhaust this piston will be held in the position shown with the face 29 seated, by the spring 35. When by the operation of the speed control mechanism the chan her 2 of the valve 4 is vented through the pipe 57, the valve moves upwardly and connects the equalizing reservoir 12 and chamber 10 to the first reduction reservoir 34 through the passages 45, 53 and 46, A reduction of equalizing reservoir pressure of for example eight pounds is thus effected which causes the piston 9 to open the valve 15 until an equal reduction in the pressure is effected in the train-pipe 14. The train-pipe exhaust passage 55 does not as usual lead directly to atmosphere but by passage 56 and cavity 47 in the valve 4 and passage 19 to the timing-reservoir 20 and chamber 18 of the piston 17 which is thus moved to the left against the spring 52 first to close the valve 24, and then upon compression of the spring 23 to connect the chamber 18 to the exhaust port 26 by way of chamber 27 as shown in Fig. 3. The trgin-pipe thus exhausts through the port 26 until the equalizing valve 15 is closed and the piston 17 is then moved immediately to the right by the spring 23 sufficiently to cut off the exhaust of the chamber 18 by way of the chamber 27. The valve 24 however is held seated until the pressure in the timing-reservoir 20 and chamber 18 falls further by leakage through the port 48 sufficiently to permit the spring 52 to return the pistons 17, 21 to the position shown in Fig. 1. The compressed air supplied to the reduction reservoir 34 from the equalizing-reservoir 12 flows by passage 33 to the outer part of the face 29 of the piston 28 and also by passages 60 to the chamber 38 of that piston. Hence, when by the fall of pressure in the timing-reservoir 20 and consequent opening of the valve 24 the passage 59 from chamber 38 is connected to the exhaust port 26, the piston 28 is moved to the left by the superior pressure on the face 29 thereby seating the head 39 of the piston so as to cut off the passage 60 from the passage 59 and exhaust port 26 and unseating the face 29 so as to connect the passage 33, 31 and thus the reduction reservoir 34 and the equalizing-reservoir 12 to the second reduction reservoir 32 with a resulting further reduction of the pressure in the train-pipe 14 effected by the equalizing valve 15. To maintain the inner chamber 35 of the piston 28 at atmospheric pressure against leakage of compressed air from passage 60 around the head 39 in the seated position, a valve 36 is opened by the piston in this position and connects the chamber 35 to the exhaust port 61. The timing-reservoir 20 may be dispensed with in which case the second reduction in tram-pipe pressure will immediately follow on completion of the first reduction. When the device is used in connection with the driver's brake valve this valve is provided with ports and passages corresponding with those of the slide valve 4.