Which TXV pressure is constant once set?

The spring pressure in a thermal expansion valve (TXV) is designed to be constant once it is set during the initial calibration process. This pressure is determined by the tension of the spring within the valve that holds its diaphragm in place and controls the flow of refrigerant. The purpose of maintaining constant spring pressure is to ensure that the TXV can respond accurately to changes in bulb pressure (which is affected by evaporator temperature) and maintain the correct flow of refrigerant to keep the system operating efficiently.

Spring pressure helps determine how much the valve opens or closes based on the temperature of the refrigerant, which ultimately controls the evaporation of the refrigerant in the evaporator coil and maintains the desired cooling effect. As long as there are no external changes or failures, the spring pressure will remain stable, facilitating a consistent operational performance of the system.

In contrast, bulb pressure, evaporator pressure, and condenser pressure are subject to fluctuations during normal operation due to changes in temperature, load conditions, and refrigerant state, and thus do not remain constant like spring pressure does. This understanding of the roles and characteristics of TXV components is crucial for effective HVAC system management and troubleshooting.