GB1146122A - Improvements in actuators - Google Patents

Abstract

1,146,122. Valves. ENGLISH ELECTRIC CO. Ltd. 21 Feb., 1968 [24 Feb., 1967], No. 9063/67. Heading F2V. [Also in Division G1] An actuator for a valve (not shown) comprises a sealed housing 9 filled with wax 13 and including a piston 11 extending into the housing, an electrical conductor 14 disposed in the wax for heating and expanding the wax so as to displace the piston 11, and circuit means (not shown) coupled to a control arm 30 for controlling the electrical energy supplied to the conductor 14 in dependence on the displacement of the piston 11. The conductor 14 is wound on ceramic support 16 and a coiled stainless steel capillary tube 17 is also disposed in the housing, compressed air being forced through the tube 17 for cooling purposes. The piston 11 acts on a plate 26 and thus on a sleeve 21A, 21B coupled to a shaft 24 of the valve against the action of a spring 27 coiled round the sleeve. Belleville washers 25 are interposed between the plate 26 and plug 22 of the sleeve 21A, 21B to prevent overloading of the shaft 24 and an overload switch 31 is provided to cut off the supply to the conductor 14 on compression of the washers 25. In use the conductor 14 is fed with a current which is the sum of a standing current, sufficient to bring the actuator to its working temperature and a control current derived from a control signal dependent on the rate of flow required through the valve controlled by the shaft 24. This control current is progressively reduced by movement of the control arm 30 on the sleeve 21A as the piston 11 is displaced to minimize overshoot and hunting. When the control signal is removed, the circuit means is arranged to cut off the standing current whilst the actuator cools, and this cooling can be accelerated by the passage of compressed air through the tube 17. Additional external cooling of the housing 9 may also be employed to further reduce time lag on the return stroke of the piston 11.