Expansion valve

Expansion valve

On its return to the evaporator from the condenser the high-temperature, high-pressure liquid refrigerant must be changed to the low-temperature, low-pressure liquid that enters the evaporator. This is usually achieved by a throttling device known as the expansion valve. When the hot liquid passes through this valve, not only will its pressure be reduced but at the same time its temperature will drop. As the pressure drops, refrigerant starts to evaporate in the valve and the heat of evaporation is taken from the refrigerant itself which causes its temperature to drop and the result is a low-temperature, low-pressure mix of liquid and vapour.