The thermostatic expansion valve is operated by a pressure difference between what two pressures?

The thermostatic expansion valve (TXV) operates based on a pressure difference that is crucial for its function in regulating refrigerant flow within an HVAC system. In the case of the correct answer, the pressure difference involves the pressure in the sensing bulb and the spring pressure within the valve itself.

The sensing bulb, which is typically located at the outlet of the evaporator, measures the temperature of the refrigerant. It converts this temperature into a corresponding pressure that acts against the force of a spring inside the valve. When the temperature rises, indicating the need for more refrigerant to be introduced into the evaporator, the pressure in the sensing bulb increases. This increased pressure overcomes the spring pressure, opening the valve and allowing more refrigerant to flow into the evaporator.

This regulation ensures that the system operates efficiently, preventing both underfeeding and overfeeding of refrigerant. As the cooling load changes, the TXV adjusts the flow of refrigerant according to the variations in temperature, which is essential for maintaining comfort and efficiency in an HVAC system.

The importance of the pressure difference in the correct response highlights the operational fundamentals of the TXV, ensuring it adjusts based on the cooling demand effectively.