GB1363298A - Hydraulic actuator - Google Patents

Abstract

1363298 Hydraulic actuators H H LOGAN 22 Nov 1971 [28 Jan 1971] 54219/71 Headings F1D and F1P An hydraulic actuator, Fig. 9, comprises a piston and cylinder 26 fed with liquid from a reservoir 20 by a gear pump 23 operated by an electric motor, there being a check valve 24 between the pump 23 and cylinder 26 which prevents flow from the latter to the former. An outlet pipe 29 leads back to reservoir 20 via a solenoid valve 30 and a metering valve 31. Remote control switch means 76, 77, 78 are used to operate the motor 34 and the solenoid 83 of valve 30, Fig. 5. If the circuit of the motor 34 is normally open then movement of a lever 76 against a micro-switch 78 closes the circuit to operate the motor 34 which in turn operates the gear pump 23 to pump fluid to the cylinder 26 through an inlet 42, Fig. 7. The piston 45 is thus raised to the required height and the lever then turned to its neutral position thus stopping the motor 34 and pump 23. Since the solenoid valve 30 is normally closed the piston, and hence its rod 47 and its load, is held in this position. The circuit for the solenoid is normally closed, so if lever 76 is moved against switch 77 to open the solenoid circuit then the solenoid will be de-energized and the valve 30 will open to permit flow to the reservoir 20 from cylinder 26. Thus the piston will descend at a rate determined by metering valve 31. If upward movement continues till the end of piston stroke a plate 61 engages the head 63 of a pin 58 to lift this against a spring 71. A spool 64 at the bottom of pin 58 engages a pivoted lever 66, Fig. 8, the other end of which is fixed to a plunger 67. Thus if piston 45 lifts pin 58 and thus the respective arm of lever 66 the other arm will be lowered. The plunger 67 holds a switch 69 thus this will be lowered to break the motor circuit and discontinue pumping. This avoids pressure build-up in the cylinder when the piston 45 reaches the end of its power stroke.