GB919714A - Hydraulic control system for a fluid actuated motor - Google Patents

Abstract

919,714. Valves; hydraulic apparatus. CESSNA AIRCRAFT CO. May 19, 1960 [June 25, 1959], No. 17722/60. Classes 69 (2) and 135. An hydraulic control system for a fluid-actuated motor 35, such as for the operation of a power shovel 45, comprises two circuit control passages 25, 26 connected to opposite ends of the motor, and a reversing spool 21 having two main operative positions in which the two circuit control passages are selectively connected to a supply passage 22, 23, including a fluid-transfer passage 27 connected to the reversing valve such that when the circuit control passage 26 is connected to the supply passage the circuit control passage 25 is connected to the transfer passage, and including a first independent valve means 42 providing fluid flow from the transfer passage into the circuit control passage 26 when the pressure in that passage falls below the pressure in the transfer passage, and when the reversing spool is in a first main operative position to connect the passage 26 with the supply passage 23 and to connect the circuit control passage 25 with the transfer passage, and second independent valve means 39 providing fluid flow from the transfer passage to a return passage when the reversing spool is in the first main operative position and when the pressure differential between the transfer passage and the return passage exceeds the pressure differential at which the first independent valve means opens. The supply passage 23 is connected via passages 17, 18 to a pump 12 and the return passage 28 connected to a reservoir 13 via pipe 30. In operation, when the shovel 45 is required to be lowered, the spool 21 is moved from the neutral position shown to the left and thereby permits fluid to flow from the supply passage 23 into the control passage 26 and then, via pipe 34, to the inner end of the ram 46. The ram then begins to drop under its own weight and, in order to prevent cavitation, the fluid on the other side of the ram is forced via pipe 33, control passage 25, transfer passage 27, ports 44 in the spool 21, and valve 42 into the control passage 26 in order to supplement the fluid being supplied by the pump. When the pressure in the latter passage increases the valve 42 is gradually closed and the pressure then developed in the transfer passage 27 opens the spring-loaded relief valve 39 so that the excess fluid is returned via passage 28 to the reservoir. To raise the shovel, the spool is moved to the right and the fluid then passes from the supply passage 22 into the passage 25 and thence to the cylinder; the fluid on the other side of the ram 46 is exhausted via passages 26, 27, 28 directly to the reservoir. Specification 918,451 is referred to.