Expansion valve is the refrigeration system is an important component, is usually installed between the reservoir and the evaporator tube. Temperature expansion valve so that the high-pressure liquid refrigerant by throttling its temperature low-pressure wet steam, and then the refrigerant absorbs heat in the evaporator to achieve the cooling effect, the expansion valve superheat changes by the end of the evaporator to control the flow valve, to prevent evaporator area utilized and knock phenomena