Patent GB-578895-A (GB)
Title: Improvements relating to control mechanism for apparatus operated by fluid under pressure
IPC: B60T13/36
Filed: 1944-04-07
Abstract: 578,895. Fluid-pressure brakes. WESTINGHOUSE BRAKE & SIGNAL CO., Ltd. (Bendix- Westinghouse Automotive Air Brake Co.). April 7, 1944, No. 6525. [Class 103 (i)] In a fluid-pressure brake system in which pressure fluid for operating brakes on a trailer vehicle is supplied from a source on the tractor vehicle and in which the trailer brakes are controlled by a relay valve device on the trailer operated by a pressure variation in a control pipe effected by a drivers valve on the tractor for service operation of the trailer brakes and also independently by a reduction in the pressure of the fluid supply from the tractor to effect an emergency application, the relay valve device comprises a single inlet and exhaust valve member, the exhaust element of which engages the one or the other of two seats in a brake application. The system shown comprises on the tractor a self-lapping drivers valve device 21 adapted to supply compressed air from reservoirs 6, 8 to brake cylinders 11, 14 by pipes 18, 20 and also to a pipe 40, 38 which controls the relay valve device 33 on the trailer. The device 33 comprises a chamber 49 connected to pipe 38 and separated by a diaphragm 77 from a chamber 48 connected by passage 78 to chamber' 46 which normally is connected to chamber 45 connected by pipes 35, 36 to the trailer brake cylinders 27. An exhaust valve 67 integral with a supply valve 63 is normally unseated as shown so that the chamber 45 and thus the cylinders 27 are connected to atmosphere through the tubular member 68 carried by the diaphragm 77, ports 74 and chamber 47. An auxiliary reservoir 29 connected by pipe 34 to chamber 43 is charged from the reservoir 8 through pipes 30, 32 and chambers 42, 43 the air supply lifting a flexible diaphragm 50 from its seat 52 against spring action. Pressure fluid supplied to pipe 38 when the drivers valve 21 is operated depresses the diaphragm 77 thus seating the tubular member 68 on the exhaust valve 67 and unseating the supply valve 63 so that pressure fluid is supplied from chamber 43 by ports 58 chamber 44 pipes 36 to the trailer cylinders 27. A stop 82 prevents the diaphragm from seating the valve 67 on the upper end of passage 64 so that the pressure in chamber 48 may equalise with that in the cylinders 27 and when this pressure slightly exceeds that in the chamber 49 the diaphragm returns to seat the valve 63. Should the pressure in the pipe 30, 32 fail the diaphragm 50 is deflected downwards to seat and unseat the valves 67, 63 respectively, with respect to the passage 64 by engagement of a member 54 on the diaphragm with a member 84 on the valves. Pressure fluid is thus supplied from the reservoir 29 to the trailer cylinders 27 by way of the chamber 43 and a restricted passage 85 in the member 84. The restricted passage 85 prevents rapid escape of pressure fluid from chamber 43 through the exhaust port prior to the closing of the exhaust valve particularly when the fall of pressure in the chamber 42 is due to leakage in the supply line. If the emergency operation is not desired the diaphragm 50 is dispensed with and either of the ports 61, 62 is connected to the pressure source, the other being closed by a plug.