GB331303A - Improvements in devices for controlling the brakes of railway vehicles - Google Patents

Abstract

331,303. McDermid, W. F. April 19, 1929. Addition to 314,179. Fluid-pressure.-In valve mechanism of the kind described in the parent Specification whereby an application of steam or compressed air brakes in a locomotive is obtained proportional to that of the automatic vacuum brakes on the train, the valve piston is subject to the normal train-pipe vacuum on one side and to the variable vacuum on the other side. In making an independent application of the locomotive brakes however the pressures above and below the piston are equalized and the piston is actuated by a hand-controlled spring device which limits the brake cylinder pressure to a predetermined maximum. The device comprises a piston 3 the lower chamber 2 of which is directly connected to the vacuum train-pipe by the passage 4 and the upper chamber 2<1> by the passage 58 and a non-return valve 59. The capacity of the upper chamber 2 is increased by a reservoir connected by passage 55 and a chamber 56. Normally the chamber 17 connected to the brake cylinder is connected to exhaust bv the chamber 23. When air is admitted to the train-pipe to apply the brakes, the piston 3 rises and its stem 51 lifts the slidable sleeve 22 to close the exhaust and engages the stem 19 of the pilot valve 20 whereby the main air or steam supply valve 16 is opened, the operation being similar to that described in the prior Specification. When it is desired to obtain a higher maximum pressure in the brake cylinder, a sleeve 22<c>, Fig. 5, of smaller diameter than the sleeve 22 is substituted, this sleeve 22<c> fitting in a sleeve 22d and exposing a smaller area of the stem 51 to the brake cylinder pressure. Independent control of the locomotive brake separately from the train brakes is obtained bv the lever 32 provided with a cam 65 which permits a spring 10 engaging the sliding head 66 of a rod 61 to lift the piston 3 through a lever 62 connected to the rod. The spring 10 determines the maximum brake cylinder pressure in independent applications. When the spring 10 is operative the cam 65 also depresses a spring plunger 69 and stem 70 to unseat a valve 67 whereby the upper and lower piston chambers 2, 2' are connected through passages 55, 74 to equalize the fluid pressures on the piston.