Simply it's a valve in a refrigeration system that controls or meters how much coolant is allowed into the evaporator.
A thermal expansion valve
(often abbreviated as TEV
, or TX valve
) is a component in refrigeration
and air conditioning
systems that controls the amount of refrigerant flow into the evaporator thereby controlling the superheating
at the outlet of the evaporator
. Thermal expansion valves are often referred to generically as "metering devices".
A thermal expansion valve is a key element to a heat pump
; the cycle that makes air conditioning, or air cooling, possible. A basic refrigeration cycle consists of four major elements, a compressor
, a condenser
, a metering device and an evaporator
. As a refrigerant passes through a circuit containing these four elements, air conditioning occurs. The cycle starts when refrigerant enters the compressor in a low pressure, low temperature, gaseous form. The refrigerant is compressed by the compressor to a high pressure-and-temperature gaseous state. The high pressure-and-temperature gas then enters the condenser. The condenser precipitates the high pressure-and-temperature gas to a high pressure liquid by transferring heat to a lower temperature medium, usually ambient air. The high pressure liquid then enters the expansion valve where the TX valve allows a portion of the refrigerant to enter the evaporator. In order for the higher temperature fluid to cool, the flow must be limited into the evaporator to keep the pressure low and allow expansion back into the gas phase. The TXV has sensing bulbs connected to the suction line of the refrigerant piping. The sensing bulbs give temperature readings to the TXV to adjust flow of refrigerant.