What is the working principle of an expansion valve?
2 Answers
Expansion valve works by detecting and collecting multiple parameters such as superheat, temperature difference between inlet and outlet air, return air temperature, and their set values. After processing by the microprocessor, it issues commands to control the opening degree of the electronic expansion valve to meet the system load requirements. The expansion valve is an important component in the refrigeration system, usually installed between the liquid receiver and the evaporator. The expansion valve causes the medium-temperature and high-pressure liquid refrigerant to throttle into low-temperature and low-pressure wet steam, and then the refrigerant absorbs heat in the evaporator to achieve the refrigeration effect. The expansion valve controls the valve flow by the change of superheat at the end of the evaporator to prevent insufficient utilization of the evaporator area and knocking phenomenon.
The expansion valve acts like the intelligent regulator of an air conditioning system, and I found it particularly crucial when studying automotive AC components. After high-pressure liquid refrigerant flows out from the compressor, it enters the expansion valve. This valve automatically adjusts its opening size based on temperature changes in the evaporator—if the evaporator temperature rises, indicating a need for more cooling, the valve opens wider to allow more refrigerant flow; when temperatures drop, it narrows to control the flow rate. During expansion, the refrigerant undergoes a sudden pressure drop, transforming into a low-temperature gaseous state, which then absorbs heat in the evaporator to cool the hot air into cold air blown into the cabin. Without the precise control of the expansion valve, refrigerant flow would become chaotic—either excessive flow causing evaporator icing and cooling failure, or insufficient flow leading to poor AC performance. This component is quite clever—it uses a small sensor to monitor temperature fluctuations, ensuring smooth circulation. For long-term stable operation of automotive AC systems, I recommend regular maintenance checks on the valve's condition to prevent clogging or aging issues that could affect comfort.
