GB918451A - Hydraulic fluid control system - Google Patents

Abstract

918,451. Hydraulic apparatus. CESSNA AIRCRAFT CO. May 4, 1960 [June 25, 1959], No. 15760/60. Class 69 (2). An hydraulic system for controlling the flow of fluid to and from a pair of opposed single-acting motors 25, 26 comprises a reversing valve 18 having two operative positions in which the pressure chambers of the motors are selectively connected to a source of fluid pressure 12 and to relief 13 and a neutral position in which both pressure chambers are isolated from the source and relief, a pressure-relief valve means 30, 31 for venting fluid under excess pressure from either pressure chamber irrespective of whether it is isolated from the source or relief by the reversing valve means and non-return valve means through which fluid can be drawn into either chamber irrespective of whether the chamber is isolated from the source or relief by the reversing valve means. The pistons of the motors are connected by a cable or chain 44 to a sprocket 41 on the shaft 42 of the boom of a mechanical shovel and the cylinders are connected by lines 23, 24 to ports 21, 22 in a valve housing 17. The ports are connected to circuitcontrol passages 19, 20 which can be selectively connected by movement of the reversing valve spool 18 to a passage 16 leading from a pump 12 or to a return passage 27 connected by a line 28 to a reservoir 13. A transfer passage 29 is formed in the housing and is connected by an adjustable check-valve 32 to the return passage 27 and by adjustable-relief valves 30, 31 to the passages 19, 20 leading to the motors. When the reversing valve 18 is moved to the left from its central, neutral position, to which it is urged by a device 46, the supply line 16 is connected by a one-way valve 36 to passage 20 leading to motor 26 and the passage 19 from motor 25 is connected to the return passage 27. When the spool is moved towards its neutral position, first passage 19 is closed, the supply continuing through passage 20 to motor 26. The inertia of the boom may cause a rise in the pressure in the motor 25. Normally, the pressures in chambers 53, 54 of the relief valve 30 are equal, but when the inertia of the boom causes the pressure in passage 19 to rise, fluid flows through a port 49 and pressure in chamber 53 rises to open a needle valve 50 and permit fluid in chamber 53 to pass through a passage 51 to drop the pressure in chamber 53. The pressure in chamber 54 acts to move a part 56 of the valve to the right away from a seating 57 so that fluid in the passage 19 passes through seating 57 and ports 52 into transfer passage 29 and through ports 68 in the spool 18 to open valve 32 and pass into the return passage. When the spool has been moved sufficiently to disconnect the supply from the motor 26, the inertia of the boom may tend to continue the movement of the piston 26 which would then be starved of fluid. In order to prevent starvation of the motor 26 and cavitation of the fluid, a part 63 of the valve 31 moves away from a seating 62 as a result of the drop in pressure in passage 20 to permit fluid in the transfer passage to pass through seating 62 and ports 64 into the passage 20. The valve housing 17 is formed with passages 10, 11 whereby it may be used in association with other valves in a multiple valve bank.