What Is a Thermal Expansion Valve?
The thermal expansion valve is used to control the opening degree of the expansion valve by the superheat of the gaseous refrigerant at the outlet of the evaporator, so it is widely used in non-full liquid evaporators. According to the different balance methods, the thermal expansion valve can be divided into internal balance type and external balance type. The thermostatic expansion valve temperature sensing system can be filled with different substances and methods. The main methods are liquid-filled, inflatable, cross-filled, mixed-filled and adsorption-filled. [1]
- Figure 1 shows the working principle of the internal balance type thermal expansion valve. As can be seen from the figure, it is composed of
- When the evaporation coil is thin or relatively long, or multiple coils share a thermal expansion valve and are connected in parallel through the separator, the refrigerant flow resistance is large. If the internal balance type thermal expansion valve is still used, evaporation will result. The superheat of the refrigerant at the outlet of the evaporator is very large, and the area of the evaporator cannot be effectively used. In this case, the internal balance type thermal expansion valve should not be used. [1]
- The installation position of the thermal expansion valve should be close to the evaporator, and the valve body should be placed vertically, not tilted or installed upside down. Because the thermal expansion valve works by the temperature sensed by the temperature sensing package, and the sensitivity of the temperature sensing system is relatively low, the time lag of transmitting the signal is large, and it is easy to cause the expansion valve to open and close frequently and the liquid supply volume to fluctuate. Installation is very important. [1]
- Various existing thermal expansion valves adjust the refrigerant flow rate by sensing the temperature change of the refrigerant at the outlet of the evaporator through a temperature sensing package. When the temperature sensor leaks, the expansion valve will be closed, and the refrigerant flow to the evaporator will be zero, causing the system to fail. To solve this problem, a two-way thermal expansion valve with a safety structure is proposed, as shown in FIG. 5. When no leakage occurs in the temperature sensing package, the principle is the same as that of the external balance type thermal expansion valve; when a leakage occurs, the throttling passage between the valve core 5 and the valve seat hole 2-1 is closed, and the limit block 1-6 and The diaphragms 1-4 move upward under the pressure of the evaporator outlet refrigerant transmitted through the pressure transmission pipe 3, and drive the valve needle 4 to move upward, so that the axial through hole in the valve core 5 is opened and becomes a throttling channel. Continue to supply liquid to the evaporator to ensure that the system continues to work. [1]