In short, the expansion valve have the valve body, temperature package, the balance tube of three major components.
The charge of the thermos bottle is the refrigerant in a saturated state of gas-liquid equilibrium, and this part of the refrigerant is indifferent to the refrigerant in the system. It is generally tied to the evaporator outlet pipe and comes in close contact with the pipe to sense the temperature of the superheated steam at the evaporator outlet. Due to the saturation of the refrigerant inside it, the pressure is delivered to the valve body at a temperature that is saturated with temperature.
One end of the balance tube is connected to the outlet of the evaporator slightly away from the temperature sensing package, and is directly connected with the valve body through the capillary tube. The role is to deliver the actual pressure at the evaporator outlet to the valve body. There are two diaphragms inside the valve body. The diaphragm moves upwards under pressure to reduce the flow of refrigerant through the expansion valve and seek a balance in the dynamics.
The ideal working condition of the expansion valve should be as the evaporator load changes in real time to change the opening to control the flow. In fact, however, the response of the expansion valve is always slowed down due to the hysteresis in the heat transfer experienced by the temperature sensing package. If we plot a time-flow diagram of an expansion valve, we will find that it is not a smooth curve, but a corrugated line. The quality of the expansion valve is reflected in the magnitude of the twists and turns. The greater the amplitude, the slower the valve response and the worse the quality.