DE-ENERGIZING SYSTEM FOR THERMAL ACTUATOR

1481817 Temperature responsive actuators GOULD Inc 27 Nov 1974 [27 Nov 1973] 51413/74 Heading G1D [Also in Division H1] A de-energizing system for a thermal actuator 10 of the type having a variable volume chamber and a piston movably positioned in the chamber, the piston being moved by pressure exerted by a thermally expansible material in the chamber, comprises as support, means for movably supporting an actuator 10 relative to the support, means for selectively coupling an actuator 10 to an energy source, and means responsive to an overload condition of an actuator 10 when supported to de-energize the same, said means being responsive to movement of actuator 10 relative to the support upon overloading and also being operatively coupled to said selective coupling means. As described, the actuator 10 is slidably mounted within a casing 30, a spring 50 biasing the actuator, in normal operation, against end stop 53. If an externally applied load 33 or the output force of the actuator 10 exceeds the pre-load force of the spring 50, the actuator 10 moves relative to the casing 30, a pin 41 mounted on the actuator body 11 breaking the connection between contacts 42, 43 and thereby breaking the heating circuit to the actuator heater. The resultant cooling of the actuator causes retraction of the piston 26 to allow spring 50 to force the actuator casing 11 against end stop 53, the heating circuit then closing. Normal operation will then resume unless the condition causing overload has not been removed in which case the circuit will be broken once more, the cycle continuing until the overload condition is rectified. The actuator 10 is of the piston cylinder type. In a prior art actuator described, the thermally expansible material within the variable volume chamber may be an azeotropic mixture of at least two liquids having different melting points, a metal hydride, or other expandable material e.g. an oil, wax or alcohol.