Thermal expansion valve is mainly composed of sensing mechanism, executing mechanism, adjusting mechanism and valve body. When the temperature of the bulb decreases, P1 < P2+F, the valve opening decreases and the refrigerant flow decreases proportionally. When the temperature of the bulb rises, P1 > P2+F, the valve opening increases and the refrigerant flow increases proportionally.Thermal expansion valve is an important automatic control component of refrigeration system, which is divided into external balance type and internal balance type according to different balance modes. It is generally installed between the liquid storage tank and the evaporator. It uses the temperature change of the temperature sensing bulb as a signal to adjust the opening of the valve and change the refrigerant flow, so that the medium-temperature and high-pressure refrigerant can be throttled into low-temperature and low-pressure wet steam, and then the refrigerant absorbs heat in the evaporator to achieve refrigeration effect.