GB872471A - Hydraulic device for a reciprocal motion subject to load reversal - Google Patents

Abstract

872,471. Hydraulic machines. KRANBAU EBERSWALDE VEB. Dec. 19, 1957, No. 39424/57. Class 69 (2). A differential piston 5a for driving a load subject to reversal, e.g. the jib of a crane, is driven by a reversible pump 1 connected in a closed system, an auxiliary pump 8 compensating for the difference in effective area of the two sides of the piston 5a. The pump 8 maintains the system filled with oil at a predetermined pressure controlled by a valve 9 by way of valves 10, 11. When pump 1 is supplying line 2, pressure fluid passes through valve 17 to chamber 7 to move piston 5a to the left, and over line 12 forces the piston 15 of valve 13 to its left terminal position (shown) whereby fluid displaced from chamber 6 is passed by valve 13 over line 3 to the suction side of pump 1. During this operation pump 8 supplies oil to the suction side of the pump 1 via valve 10. Should the load on the piston-rod 5 reverse, the consequential drop in pressure in chamber 7 and line 12 causes piston 15 to be moved to the right by spring 14 to throttle the flow of oil from chamber 6 to line 3 and thus brake the piston 5a until the pressure in chamber 7 and line 12 builds up to move valve piston 15 to the left to remove the braking action on piston 5a. When pump 1 is supplying line 3, pressure fluid passes via line 19a and a valve 16 to chamber 6 to move piston 5a to the right, whereby oil is returned to the suction side of pump 1 over line 2. At the same time, pressure fluid via line 19 moves the piston 20a of valve 17 to the right so that the excess oil displaced from chamber 7 is passed over line 18 back to a reservoir 22. Should the load on the piston 5a reverse, the piston 20a is moved to the left by spring 21 and the valve 17 throttles the return of oil over line 18 to brake the piston 5a. Two or more working cylinders may be used with their pistons 5a connected hydraulically in parallel.