GB740429A - Improvements in or relating to selector valves for hydraulic systems - Google Patents

Abstract

740,429. Fluid-pressure servomotor-control systems. BENDIX AVIATION CORPORATION. Oct. 22, 1953 [Nov. 3, 1952], No. 29227/53. Class 135. A manually-actuated valve for controlling the flow of pressureliquid to a hydraulic motor comprises a body 10 having an inlet 11 for pressure liquid supplied by a pump 12 having a relief valve 28, outlets 15, 16 to motor cylinders 17, 18 interconnected by a pipe 19, a return port 14 connected to a reservoir 13, and main and pilot bores 30, 50 respectively for piston valves 31, 51, the main valve being slidable from a central or neutral position to either of its end positions by pressure liquid the flow of which to either end of the main bore is controlled by the pilot valve. The main piston valve 31, which is centralized by springs 32, 33, has a bore 31a having enlarged ends 31b, 31c separated from the central part by spring-loaded ball valves 60, 62 and closed at their ends by members 40, 41 retained in position by circlips. The piston has lands which control the flow of liquid between the inlet 11, the motorcylinders 17, 18 and the return port 14 to the reservoir. The pilot piston valve 51 has lands 51a, 51b which control the flow of pressure-liquid from the inlet 11 through annular control ports 50a, 50b to the ends of the main bore and from the latter to end chambers in the pilot bore connected by ducts 53 and an annular port 30c in the main bore with the return port 14. The lands 51a, 51b are formed with reduced ends 70 which permit leakage from the annular ports 50a, 50b into the end chambers of the pilot bore, so as to ensure the ready exhaust of liquid from either end of the main bore when pressure liquid is supplied to the opposite end. The pilot piston valve is reciprocable by a hand lever 21 connected by a link to the lower end of a floating lever 23 connected at an intermediate point to the pilot valve and at its upper end to the rod of the power piston 17a. The' lever 23 thus forms a follow-up for returning the pilot valve to its central or neutral position. The interconnection of the power cylinders by the pipe 19 prevents the formation of a vacuum in either of the cylinders in the event of the powerpiston 18a creeping to the right under the action of a load tending to move the piston in that direction. In operation, in order to move the pistons 17a, 18a, say, to the right, the lever 21 is moved clockwise thus displacing the pilot piston 51 to the left and permitting flow of pressure liquid, e.g. at from 25 to 50 p.s.i. maintained by the spring-loaded valve 62, to the left end of the main bore 30 and displacement of the main piston 31 to the extreme right of its travel. During this time, liquid is displaced from the right end of the main bore into the corresponding end of the pilot bore and thence via the passages 53 and the annular port 30c to the return port 14. The displacement of the piston 31 cuts off the flow of pressure-liquid from the inlet 11 through the bore 31a and past the valve 62 to the return port and the pressure in the inlet rises to the pump discharge pressure, e.g. 1000 p.s.i. The high-pressure liquid flows from the inlet end, via the annular port 30a in the main bore and the motor port 15, to the left end of the cylinder 17, thus displacing the liquid from the right end of the cylinder through the pipe 19 to the left end of the cylinder 18, the piston of which thus moves to the right. The liquid displaced from the right end of the cylinder 18 flows through the port 16 and the annular port 31d in the main bore into the passage 31a and past the valve 62 to the return port 14. The leftward movement of the piston 17a results in the return of the pilot piston 51 to its original position.