GB1427503A - Control system for fluid-driven motors - Google Patents

Abstract

1427503 Valves CATERPILLAR TRACTOR CO 8 Aug 1974 [8 Aug 1973] 35040/74 Heading F2V [Also in Division F1] In the circuit shown, Fig. 1, in which a main control valve 17 controls an actuator 10 and is itself controlled by a pilot valve 25 valves 78, 79 prevent cavitation if the actuator tends to overrun by opening to connect opposite sides of the piston. When the piston is being retracted, fluid is supplied from an inlet 16 of valve 17 through a passage 69 to port 11 of the actuator and fluid returns from a port 12 through a passage 64 to a reservoir 14. If the actuator starts to overrun, a pressure drop occurs in the passage 69 which is communicated to a chamber 84 through a bore 85. At the same time, a pressure increase occurs in the passage 64 and this is transmitted through the drain passage 74 to a passage 75. This pressure difference across the valve 78 lifts it against a spring 86 so that fluid being discharged from the port 12 is supplied to the port 11. Valve 29 opens in a similar manner, if required, when the piston is being extended. The pilot valve has a " float " position F, Fig. 4, in which the actuator 10 is free to move in either direction as determined by external forces. In this position pilot pressure from an inlet 28 is transmitted to a spring chamber 52 of valve 17 so that port 11 of the actuator is supplied with fluid whilst port 12 is connected to reservoir. In addition a groove 91 in the pilot valve is connected to the reservoir. This allows pressure in a line 108 to move a spool 106, of a float valve 93, to the left to close a line 99 and connect a line 95 to the reservoir. This vents the spring chamber 84, Fig. 1, to reservoir so that the valve 78 is lifted from its seat by pressure in the passage 69 which acts against a shoulder 87, or in response to pressure in passage 75 received through passage 74.