There are two main forms of self-acting temperature control available on the market: Liquid filled systems and vapour tension systems. Self-acting temperature controls are self-powered, without the need for electricity or compressed air. The control system is a single-piece unit comprising a sensor, capillary tubing and an actuator.
If a temperature sensitive fluid is heated, it will expand. If it is cooled, it will contract. In the case of a self-acting temperature control, the temperature sensitive fluid fill in the sensor and capillary will expand with a rise in temperature
