Wax thermostatic element
The wax thermostatic element was invented by Sergius Vernet (USA) in 1936. The principal application of the wax element technology is for the production of automotive thermostats. The first applications of this technology in the plumbing and heating industries were in Sweden (1970) and in Switzerland (1971).
Wax thermostatic elements permit the transforming of thermal energy into mechanical energy. Their working principle is based on the large increase in the thermal expansion of waxes when they pass from the solid to the liquid state. The range of application includes but is not limited to the automotive industry, military and civil aviation, domestic heating (eg. thermostatic radiator valves), plumbing, industrial, fire, and agriculture.
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http://en.wikipedia.org/wiki/Wax_thermostatic_element