Automatic Expansion Valves are designed to maintain a higher and constant suction pressure in the evaporator, regardless of variations in heat load.
They are very precise operating valves. Once well regulated it maintains
Practically constant the temperature of the evaporator, hence they are used when exact temperature control is desired.
They work as follows: when the compressor starts to work,
Decreases the refrigerant pressure in the evaporator. This causes the valve needle to open, allowing refrigerant to enter the evaporator. While the compressor is running, the automatic valve maintains a constant pressure in the evaporator.
When the compressor stops working, the refrigerant pressure in the evaporator begins to rise immediately. This increase in pressure causes the valve needle to close.
