How does a thermostatic expansion valve respond to low temperature at the sensing bulb?

A thermostatic expansion valve (TXV) is designed to regulate the flow of refrigerant into the evaporator based on the temperature of the refrigerant vapor that it senses. When the temperature at the sensing bulb is low, it indicates that there is a lower demand for refrigerant within the evaporator—typically because the evaporator is cool and has sufficient refrigerant.

In response to this low temperature, the thermostatic expansion valve decreases the flow of refrigerant to the evaporator. This helps prevent overfeeding of the evaporator, which could lead to inefficient operation or potential flooding of the compressor with liquid refrigerant.

By controlling the refrigerant flow in this manner, the TXV ensures that the system operates efficiently and that the maximum amount of heat can be absorbed by the refrigerant in the evaporator, thereby maintaining the desired cooling capacity without causing system imbalance. The valve adjusts dynamically, decreasing flow when temperatures drop, to maintain optimal performance throughout various operating conditions.