Wax thermostatic element

The development of the automatic thermostat in the 1930s solved this problem by ensuring fast engine warm-up.

[4] The first thermostats used a sealed capsule of an organic liquid with a boiling point just below the desired opening temperature.

Conveniently this was also the hottest accessible part of the cooling circuit, giving a fast response when warming up.

A larger bypass is often provided, through the cylinder block and water pump, so as to keep the rising temperature distribution even.

This increased both the working temperature of the engine, thus its efficiency, and also the heat capacity of the coolant by volume, allowing smaller cooling systems that required less pump power.

This most common modern form of thermostat now uses a wax pellet inside a sealed chamber.

The extent of the chains is usually determined by the melting characteristics demanded by the specific end application.

The temperature sensing material contained in the cup transfers pressure to the piston by means of the diaphragm and the plug, held tightly in position by the guide.

Flat diaphragm elements are particularly noted for their high level of accuracy, and therefore mainly used in sanitary installations and heating.

Squeeze-Push elements contain a synthetic rubber sleeve-like component shaped like the 'finger of a glove' which surrounds the piston.

As the temperature increases, pressure from the expansion of the thermostatic material moves the piston with a lateral squeeze and a vertical push.

[citation needed] Hysteresis is the difference noted between the upstroke and down stroke curve on heating and cooling of the element.