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

The thermostatic expansion valve (TXV) regulates the flow of refrigerant into the evaporator based on the conditions of the system. The operation of the TXV hinges on the pressure difference between the sensing bulb pressure and spring pressure.

The sensing bulb, located at the outlet of the evaporator, senses the temperature of the refrigerant. As the temperature of the refrigerant increases, the pressure in the sensing bulb also increases. This pressure acts against a spring inside the TXV. The balance or differential between the pressure exerted by the sensing bulb and the counteracting spring pressure is what allows the TXV to modulate the opening of the valve. If the refrigerant is hot, indicating a need for more cooling, the sensing bulb pressure overcomes the spring pressure, causing the valve to open wider, allowing more refrigerant to flow into the evaporator to absorb heat.

Thus, the correct answer identifies this crucial interaction between the pressures to maintain system efficiency and performance.