Expansion composition

An electrically stimulated actuator apparatus for use in a thermostatic control valve, the apparatus comprising

• a thermal and electronically conductive housing having two end walls connected together by a side wall for defining a closed volume cavity,
• a piston extending into the cavity of the housing, the piston passing through one of the end walls and moveable away from the other end wall to increase the size of the cavity, the piston spaced from the side wall, and
• an expansion composition held in the cavity in communication with an end and side of the piston, the expansion composition including an electrical isolator being formed to increase in temperature as electrical current flows therethrough and configured to expand volume from a pre-determined normal operating volume to a pre-determined expanded volume as the temperature of the expansion composition increases and electrical conductor particles dispersed throughout the electrical isolator and being present in an amount sufficient to conduct electrical current through the electrical isolator when the electrical isolator has a volumetric size that is less than the predetermined expanded volume;
• a first electrical contact attached to the housing;
• a second electrical contact attached to the piston;
• a source of electrical current for passing a current flow between the two electrodes;
• the piston being configured to move away from the cavity when the expansion composition expands in volumetric size to a volume greater than the pre-determined normal operating volume;
• and
• wherein the expansion of the expansion composition is determined by the amount of current flow between the electrodes, the extent the piston extends into the cavity and heat flows into and out of the cavity through the thermally conductive housing.