Marks: 5M

Topic: - Va-pour Compression Refrigerator System

Year: May : 2015

Sem: 8

The valve has a diaphragm having spring force and atmospheric pressure acting on top of it and evaporator pressure acting below it. The diaphragm operates the needle valve.

The valve maintains a constant evaporator pressure regardless of load on evaporator and so is also called ‘constant pressure expansion valve’.

When evaporator pressure falls, diaphragm moves downwards to open the valve, allowing more liquid refrigerant to enter and thus increasing evaporator pressure till the desired pressure is reached. This pressure is set by adjusting the tension of the spring with the help of adjusting screw.

Similarly, diaphragm moves upwards when evaporator pressure rises. This decreases valve opening and in turn the refrigerant flow also, leading to drop in the pressure till the desired value is reached.

This valve is used with dry expansion evaporators where load is relatively constant.