GB918452A - Hydraulic control system - Google Patents

Abstract

918,452. Hydraulic apparatus. CESSNA AIRCRAFT CO. June 10, 1960 [July 3, 1959], No. 20503/60. Class 69 (2). An hydraulic system for controlling the operation of a fluid-actuated motor 18 and for preventing cavitation therein when large inertia forces are transmitted thereto comprises reversing valve means 30 having two operative positions for connecting a supply passage 1 with one or other of circuit-control passages 36, 37 communicating respectively with the opposite ends of the motor, the other control passage being connected to a return passage 38, and a neutral position in which both circuit-control passages are blocked from the supply passage and the return passage, and independent valve means 43, 44 effective when the reversing valve means is in its neutral position to afford flow of fluid from the return passage directly into either of the circuit control passages when the pressure in the latter drops below the pressure in the return passage. The motor, which may be of the piston-and-cylinder type, or, as shown, the vane type having its rotor 24 connected to the boom 26 of a power shovel, has its chambers 50, 51 connected by lines 19, 20 to ports 39, 40 in a valve housing 17. The ports are connected to the circuit-control passages 36, 37 which can be selectively connected by movement of the reversing valve spool 30 to the passage 16 leading from a pump 12 or to the return passage 38 which is connected by a line 22 to a reservoir 13. When the spool 30 is moved to the right, the passage 36 is connected by a one-way valve 35 to the supply passage 16 so that fluid pressure is communicated to the chamber 50 to move the boom counterclockwise, fluid from chamber 51 passing through passage 37 and return passage 38 to the reservoir 13. When the spool is returned to its neutral position, the inertia force of the boom 26 and shovel 28 may cause an increase in the pressure in the chamber 51, which pressure is transmitted to passage 37 and, at a predetermined value, opens an adjustable pressure-relief valve 42, such as is described in Specification 918,451, to relieve the pressure and pass fluid into the return passage 38. The inertia force of the boom may also cause a drop in the pressure in chamber 50 to a value below that in the return passage 38. The drop in pressure causes the valve 43 to open and fluid in the return passage to flow into the passage 36 and the chamber 50 to prevent cavitation therein. Similar action occurs when the spool 30 is moved to the left to move the boom clockwise. The valve housing is formed with passages 10, 11 to permit the valve to be used in association with other valves in a multiplevalve bank.