GB553373A - Improvements in control valves - Google Patents

Abstract

553,373. Fluid-pressure brakes. BENDIX AVIATION CORPORATION. Sept. 2, 1941, No. 11224. Convention date, Feb. 19. [Class 103 (i)] Two diaphragms of a control valve for a fluidpressure brake that are subject respectively to controlling pressure and to brake cylinder pressure are interconnected by a lever the arms of which can be varied to vary the cylinder pressure established by a given control pressure. A vacuum system for a tractor and a trailer vehicle is described in which the pistons of both cylinders are normally subject to vacuum on both sides the tractor cylinder being directly controlled and that in the trailer cylinder by the valve which compresses diaphragms 60, 62 dividing the casing into chambers 64, 66, 68 connected respectively to a control pipe at 70, to a vacuum reservoir on the trailer by passages 74, 75 and to the chamber in one side of the trailer brake piston at 76. The rod 84 of diaphragm 62 operates through lever 82, atmosphere and valves 78, 80. The diaphragms are connected at 86, 90 to a lever 88 which comprises a pair of members 94, 96 pivoted on a trunnion 100 slidable in a slot 98 in the members. By turning a right-and-left handed screw 102 which secures into the trunnion and the casing, the trunnion can thus be adjusted in the slot to vary the effective arms of the lever. Normally vacuum exists in the chamber 64 so that the balves 80, 78 are respectively open and closed and the cylinder chamber.. connected to passage 76 is thus connected to the vacuum reservoir. To apply the brakes air is admitted to chamber 64 whereby the valve 80 is first closed and the valve 78 is opened as shown. When the pressure in chamber 68 acting on diaphragm 62 balances that in the chamber 64 acting on the diaphragm 60 the valve78 closes. If for example, the area of diaphragm 60 is double that of diaphragm 62 and the distance of pin 86 from the trunnion is double that of the pin 90 the pressures in the two chambers 68, 64 will be equal but by moving the trunnion outwardly, the pressure established in chamber 68 will be greater than that in chamber 64. In the system shown the chamber on one side of the tractor cylinder and to the reservoir on the trailer are connected to a pipe that is constantly connected to the engine manifold. The drivers valve is connected to the manifold and to a pipe that is directly connected to the other chamber of the tractor cylinder and to the passage 70 of the valve shown in Fig. 2. The ratio of the trailer braking pressure to that of the tractor is thus determined by the ratio of the arms of the lever 88.