GB567858A - Apparatus for controlling fluid pressure - Google Patents

Abstract

567,858. Hydraulic machines. STEPHENS, W. T. Aug. 12, 1943, No. 13088. [Class 69 (ii)] A valve housing 32 has connections 28, 30 with the two sides of a motor 20, connections 38, 40 with the inlet and outlet of a pump 36, and openings 56, 58 to and from a reservoir 34. The pump delivers through a check valve in the housing, and a plunger 69 controls communication between reservoir opening 58 and pump inlet connection 38 and also controls communication between a passage 66 having valved communication with passages 71, 74 connected with the motor ends and a passage 60 leading to the pump inlet. In the " hold " position of the control valve 48, show in Fig. 2, and in the " float " or extreme righthand position, in which the passages 71, 74 are in free communication, the pump is cut off from connection with the motor, and liquid circulates between reservoir and pump through openings 56, 58. In the hold position, the pump delivers to a passage 52 and thence freely into passage 56 opening directly into the reservoir, and liquid passes freely through reservoir outlet 58 to the pump inlet a passage 64 to which the pump delivers is closed. Movement of the control valve in either direction to the raise or lower position opens one of the passages .71, 74 to supply from the passage 64, and connects the other through passage 66 and apertures 94 in plunger 69, which is then raised to close communication through reservoir outlet 58 except for a small aperture in the plunger top, with the pump inlet passage 60; at the same time the connection between passage 52 and reservoir inlet passage 56 is closed. A byepass controlled by an adjustable spring- pressed valve connects the two sides of the pump when delivery pressure is excessive. A second byepass valve allows excess of pump liquid supplied to the piston-rod side of the motor to return to the suction side of the pump.