Which forces work to close the TEV valve?

• A. Evaporator pressure
• B. Spring pressure
• C. Evaporator pressure and Spring pressure
• D. Bulb pressure

Answer: (C)

In a thermostatic expansion valve, the valve position is set by balancing three forces on the diaphragm: evaporator (low-side) pressure, the pressure from the thermostatic sensing bulb, and a spring. The spring provides a constant closing bias. When evaporator pressure rises, it pushes the diaphragm toward the valve seat, increasing the closing force. The bulb pressure, driven by the sensed temperature, tends to push in the opposite direction to open the valve. Therefore, the forces that close the TEV valve are evaporator pressure and the spring, with the bulb pressure acting to open and modulate the opening.