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Thermostat switches are used in temperature control systems to regulate air or liquids and can be used in both commercial and domestic applications. The two main types are capillary and bimetallic thermostats.

RS offer a range of thermostat switches such as enclosure thermostats, mechanical HVAC thermostats, digital and programmable HVAC thermostats, digital and smart thermostats with Wi-Fi.

### What Does a Thermostatic Switch Do?

Thermostats regulate the temperature of liquid in a tank, or in conjuction with air conditioning units to monitor the air in a room or system. The thermostat simply switches the system off or on whenever necessary so that a constant temperature can be maintained.

### Capillary Thermostat Switches

These consist of a sensor, capillary tube, diaphragms, a probe and an expansion medium. When the liquid heats up and expands, the temperature sensor is heated allowing for it to be converted into displacement in the diaphragm. The contacts within the closed circuit system can be opened or closed by this displacement due to pressure.

Due to their accuracy and easy installation, they are widely used to control air and water temperatures and are suitable for use in storage heaters, hot tanks and boilers to control hot water.

### Bimetallic Thermostat Switches

These consist of a strip of two different metals with different coefficients of linear expansion. The bimetallic strip acts as an electric contact breaker in an electric heating circuit. When the desired temperature is reached, the circuit is broken.

The strips of metal are bolted together. A bridge is then created in the electrical circuit and is connected to your heating system. The strip carries electricity through the circuit when the heating is on. When the strips get hot, both of the metals expand but one more so than the other. The hottest metal bends and opens the circuit. Once the circuit is open the electricity switches off and the heating cuts out.

Once the heating is off, the room cools down which in turn cools down the strip of metal and allows it to go back to its original shape. When it cools, the metal goes back into the circuit and switches the heating back on as the electricity flow has been re-established. The metal strip takes a while to expand and contract so the heating is not constantly switching on and off every few seconds.



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