DE2758553

An electro-thermal fluid displacement actuator includes a fixed volume boiler chamber and a variable volume actuation chamber formed by a ported partition being received in the main body of the actuator between a positive temperature coefficient heat source for the contained fluid and an elastomeric diaphragm. Upon energization of the heat source, a portion of the contained fluid vaporizes to increase the pressure in the boiler chamber resulting in displacement of some of the remaining fluid through the partition ports and into contact with the diaphragm to drive the same and the piston assembly mounted thereon through the predetermined stroke thereof. A positive temperature coefficient heater for enhancing the response time of thermal actuators is disclosed. The PTC heater is formed of a generally low resistance material that has an anomaly temperature above which the resistance of the heater increases dramatically. The anomaly temperature is chosen to substantially match the phase change temperature of a thermally expansive medium useful to power the actuator. The heater is self-regulating and provides a maximum surface area for heating the medium rapidly with a minimum of thermal ? , and energy use. Preferably, the heater is formed of BaTiO3 in the general shape of an elongated annular cylinder.