Which pressure controls the operation of an internally equalized TXV?

An internally equalized thermostatic expansion valve (TXV) operates by modulating the flow of refrigerant into the evaporator based on the pressure difference created by the refrigerant's saturation vapor temperature at both the inlet and outlet of the evaporator. This pressure difference is directly influenced by the vapor pressure readings taken at the inlet and outlet of the evaporator. The TXV uses this information to maintain the desired superheat, ensuring that the refrigerant is efficiently evaporated and preventing liquid refrigerant from returning to the compressor.

By measuring the pressure of the refrigerant gas at the evaporator outlet (where the temperature is directly correlated to its latent heat of vaporization) against the pressure of the refrigerant gas entering the evaporator, the TXV can adjust how much refrigerant enters the evaporator. This mechanism is crucial for maintaining system efficiency and preventing compressor damage.