What is the working principle of an expansion valve?
2 Answers
The working principle of an expansion valve is to use an electronic expansion valve to regulate the refrigerant superheat at the evaporator outlet. It can collect superheat signals through temperature sensors and pressure sensors installed at the evaporator outlet, and sometimes also utilizes temperature sensors placed in the middle of the evaporator to measure the evaporating temperature. Feedback control is then applied to adjust the opening degree of the expansion valve. An electronic expansion valve mainly consists of four parts: 1. Rotor, which functions like the rotor of a synchronous motor and is connected to the valve stem to control the valve opening size; 2. Stator, equivalent to the stator of a synchronous motor, converting electrical energy into a magnetic field to drive the rotor's rotation; 3. Valve needle, driven by the rotor, with a conical tip that moves up and down to regulate flow; 4. Valve body, typically made of brass.
With over 20 years of car repair experience, inspecting an expansion valve is as simple as checking a faucet switch. It's installed on the thin pipe between the AC condenser and evaporator, and its job is to precisely release high-pressure liquid refrigerant. The principle relies on the pressure pin behind the valve core's temperature-sensing bulb. The bulb is attached to the evaporator's outlet pipe—when it detects higher return gas temperature, the gas inside expands, pushing the pin forward to open the valve wider, allowing refrigerant to flow freely into the evaporator. If the temperature drops, the gas contracts, retracting the pin to reduce the valve opening and restrict flow. This continuous adjustment ensures stable heat absorption by the evaporator. If the valve core jams, the AC either won't cool or will freeze up completely.
