Self Temperature Control Valves / ST series 

ST-series is completely self-operated and requires no external power source or other expensive instrumentation the valve.

The operation of ST-series is fairly simple. A pre-measured amount of liquid fill is drawn into the thermal system filling the upper diaphragm chamber, the capillary tube, and most of the bulb. As the controlled temperature increases, the volatile liquid fill in the sensing bulb begins to vaporize and creates pressure on the sealed system. 

This pressure drives the valve stem, closing direct acting valves, or opening reverse acting valves.

Principles of operation :
A change in temperature at the sensor will cause the liquid filling to expand or contract. If the liquid expands it will apply a force on the thrust pin which, in turn, will cause the valve plug to move. As the liquid contracts the force on the valve plug reduces and a spring reverses its direction of travel.

For heating applications the valves will be normally open and will close against a rise in temperature.
For cooling applications the valves will be normally closed and will open against a rise in temperature.