GB907000A - Improvements in and relating to liquid servo motors - Google Patents

Abstract

907,000. Liquid-pressure servomotor-control systems. ENGLISH ELECTRIC CO. Ltd. March 23, 1959 [March 21, 1958], No. 9206/58. Class 135. In a liquid-pressure servomotor for actuating, e.g., the speed controller on an A.C. mine winder motor, comprising an output piston 10 coupled to the driving shaft 29 of the speed controller and to a floating lever 13 to which is coupled a slide valve 12 and a control member 16 so that on movement of the control member the slide valve is moved to move the piston to a position corresponding to the position of the control member and on reaching that position the slide valve is returned to its closed position, pressure liquid is supplied to the servomotor by main and auxiliary pumps 18, 19 respectively, delivering simultaneously at the same pressure on the adjustment of pressure relief valves R 1 , R 2 . The capacity of the pump 18 is 20-10 times that of the pump 19 and at a predetermined point in the stroke of the piston a cam 31 on the shaft 29 engages a cam-follower to automatically open a valve 32 against its spring to unload the pump 18 so that the piston in the latter part of its stroke leftwards travels more slowly to reduce the speed of the speed controller. To ensure that the high inertia of the parts operated by the shaft 29 does not cause the piston to continue to travel at the same speed after the main pump 18 has been bypassed, a further cam 35 mounted on the shaft 29 momentarily closes a valve 34 to restrict flow to sump from the servomotor cylinder, flow then taking place through a small-bore pipe by-passing the valve 34. A non-return valve 33 prevents the pump 19 from discharging to exhaust when the pump 18 is unloaded and a non-return check valve 37 allows of independent adjustment of the pump pressures whilst both pumps are running.