Describe the construction and working of of thermostat valve used in cooling system.

Describe the construction and working of of thermostat valve used in cooling system.
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1 Answer

Answer :

Bellows type thermostat valve 

Construction: It consists of metallic bellows filled with some volatile liquid like acetone, alcohol or ether which boils between 75-850C. When after start the engine is warming up it is desired that cooling system should not operate during this period thermostat valve remains closed as liquid inside has not changed its state.

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Working: Bellows type Thermostat 

As the coolant temperature reaches a predetermined value (about 800) the liquid inside the thermostat is converted into vapour which exerts a pressure on the valve, which begins to open, so that the water circulation though the radiator starts. The valve then opens gradually further as the water temperature rises, until it is fully open bat about 950C -990C


OR


Wax type Thermostat Valve: Construction: It is made up of copper loaded wax having high coefficient of volumetric thermal expansion. A cylinder or capsule is filled with wax and thrust pin is inserted in it. A flexible rubber sleeve, which surrounds the pin is sealed at the top to prevent escape of the wax. As the wax melts and expands, the thrust pin is forced out of the capsule so opening the valve.

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Working: As the coolant is heated it transmits its heat to the copper loaded wax having high coefficient of volumetric thermal expansion (0.280 per 0C) which expands so that the rubber plug contracts against the plunger and exerts a force on it upwards so that it moves vertically. This movement of plunger opens a valve in the thermostat to allow coolant to flow through the radiator. 

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