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| Illustration 1 | g00298358 |
(1) Diaphragm (2) Spring (3) Needle valve (A) Inlet to the evaporator (B) Outlet from the evaporator | |
The expansion valve changes refrigerant of high temperature liquid into a low temperature liquid. The expansion valve provides a metered restriction which allows the liquid at high pressure to be reduced to a liquid at low pressure. The liquid refrigerant expands as the refrigerant passes through the metered restriction. This expansion reduces the pressure.
The lower pressure reduces the boiling temperature of the refrigerant. Due to the change in pressure below the boiling temperature, some refrigerant may change to a vapor. The refrigerant that is at low pressure flows from the expansion valve to the evaporator. Latent heat is absorbed by the refrigerant in the evaporator. Absorption of latent heat changes the refrigerant from a liquid to a vapor.
The expansion valve is a device that controls the flow of refrigerant to the evaporator. Not enough refrigerant in the evaporator will cause the refrigerant to flash to vapor too early. The heat transfer in the evaporator is reduced if the refrigerant evaporates too soon. Too much refrigerant in the evaporator will flood the coils. Flooding of the evaporator coils lead to liquid refrigerant in the compressor. The liquid refrigerant could damage the compressor.
The expansion valve is a block type expansion valve. The outlet from the evaporator is located on the upper portion of the expansion valve. The inlet to the evaporator is located at the lower portion of the expansion valve. A diaphragm is attached to the needle valve. The diaphragm is located on the top of the expansion valve. The expansion valve is controlled by the change in temperature of the refrigerant vapor that leaves the evaporator. Some of the refrigerant that leaves the evaporator enters the area under the diaphragm. As the temperature of the refrigerant vapor increases, the pressure increases. When the pressure of the refrigerant increases the diaphragm is forced upward. The diaphragm moves upward and the movement opens the needle valve. The needle valve opens the expansion valve. More refrigerant is allowed to enter the evaporator with the opening of the expansion valve. As more refrigerant enters the evaporator, the temperature of the refrigerant that leaves the evaporator lowers. As a result, the pressure of the refrigerant that is under the diaphragm lowers. Less pressure on the diaphragm in the expansion valve closes the valve. The flow of refrigerant into the evaporator is reduced when the expansion valve is closed. Refrigerant flows from the accumulator through lower portion (A) of the expansion valve. The refrigerant leaves the evaporator through upper portion (B) of the expansion valve.