The thermal expansion valve, also known as a temperature-sensing expansion valve, has its temperature sensing bulb tightly attached to the outlet pipe of the evaporator. Therefore, the expansion valve can automatically adjust the refrigerant flow supplied to the evaporator according to the pressure changes of the refrigerant gas at the outlet of the evaporator.
According to the structure and working principle of the thermal expansion valve, it can be divided into two types: internal balance thermal expansion valve and external balance thermal expansion valve.
The internal balance thermal expansion valve can adjust the size of the spring pressure P2 by adjusting the regulating screw, thereby changing the system's cooling capacity. It is suitable for air conditioners with short evaporation processes and relatively small flow resistance.
The external balance thermal expansion valve is different from the internal balance thermal expansion valve in that an external balance pipe is connected from the evaporator outlet end to the upper side of the valve plate. Its balanced pressure comes from the evaporator outlet, which can compensate for the excessive pressure drop caused by the long evaporation process, ensuring the cooling effect.
Therefore, for evaporators with long processes, large flow resistance, or high cooling capacity, an external balance thermal expansion valve should generally be selected.
Currently, in the refrigeration systems of new energy-saving frequency conversion air conditioners, fast-acting electronic expansion valves controlled by microcomputers are used, which can more accurately, quickly, and significantly adjust the load of the refrigeration system. The electronic expansion valve mainly consists of a stepper motor and a needle valve. The needle valve is composed of a valve stem, valve needle, and throttling hole. The valve body is engaged with the valve stem through internal threads. When the stepper motor runs, the shaft rotates, and the valve stem moves up and down under the push of the internal thread, changing the opening degree of the needle valve, thereby adjusting the refrigerant flow.
Edited and organized by the Beijing AUX Air Conditioning After-sales Service Center on September 23, 2011.
AUX Air Conditioning Repair Answer: The Function and Classification of Air Conditioner Thermal Expansion Valves