The Metering/Expansion Device

During the expansion process, an expansion/metering device or fixed restriction device such as a capillary tube is placed in the liquid line.

The expansion device controls the flow of refrigerant to ensure that the correct amount of refrigerant matches the rate at which the refrigerant is being evaporated as it passes through the evaporator ensuring the correct transfer conditions are achieved during the evaporation stage.

The metering device also maintains a constant pressure differential between the condenser and the evaporator so that the refrigerant saturation temperature is above that of the surrounding air in the condenser and below the temperature of the area to be cooled in the evaporator.

The basic function of the Metering/Expansion device is to:

• Reduce the system pressure (and temperature).

• Regulate the flow of refrigerant through the evaporator and the system.