Expansion valve working principle and correct maintenance Let me talk about commonly used ones, such as Danfoss danfoss expansion valve, Emerson EMERSON expansion valve (Aike ALCO expansion valve), Spoland SPOLAN expansion valve, etc. Generally, small and medium-sized air conditioning and refrigeration equipment use thermal expansion valves, large central air conditioning And the equipment uses electronic expansion valve.
Expansion valve It is an important component of a refrigeration device and one of the four basic equipments in a refrigeration system. It achieves throttling from condensing pressure to evaporating pressure and controls the flow rate of refrigerant. Although its volume is small, it has a huge effect, and its work is good or bad, which directly determines the working quality of the entire system. But in practice, the operation of the expansion valve is often overlooked, making the expansion valve a dead end in the operation and maintenance of air conditioning. Regular inspection and adjustment of the expansion valve is of great significance to the operating life of the air conditioner, saving energy, and reducing operating costs. Working principle of expansion valve: thermal The expansion valve controls the superheat of the gaseous refrigerant at the outlet of the evaporator to control the flow of refrigerant into the evaporator. According to different balancing methods, the expansion valve is divided into external balance type and internal balance type. In the special air conditioner, because the evaporator has a branch and uses a shower head liquid separator, the pressure drop is relatively large, resulting in different inlet and outlet temperatures of the evaporator. In this case, the use of an internal balance expansion valve will cause the thermal expansion valve to close excessively due to the low temperature of the evaporator outlet, so that the expansion valve loses the function of regulating the liquid supply to the evaporator. Therefore, the special air conditioners all use external balance expansion valves. The air-cooled special air conditioners currently used, such as ISOVEL, AIREDELE and Faya, adopt this structure. The external balance type can avoid the situation that the expansion valve is excessively closed, and ensure that the evaporator with a pressure drop also receives normal liquid supply. The structure of the expansion valve is shown in Figure 1: The thermal expansion valve consists of an induction mechanism, an actuator, an adjustment mechanism and a valve body. The induction mechanism is filled with freon working fluid, and the temperature sensing bag is set at the outlet of the evaporator. Due to the influence of superheat, there is a temperature difference between the temperature at the outlet and the evaporation temperature, which is usually called superheat. After sensing the temperature of the outlet of the evaporator, put the whole sensing system at the corresponding saturation pressure as shown in Figure 1. This pressure will be transmitted to the ejector rod through the diaphragm to the valve core. The diaphragm above the pressure chamber only exists, and there is a balance between the spring force of the adjusting spring and the evaporating pressure below the diaphragm. Sometimes it means that the evaporator's thermal load is too large and the outlet superheat is too high. Transmitting this pressure signal causes the spool to move down, the expansion valve opens and the refrigerant flow increases proportionally. Conversely, when the expansion valve opens, the refrigerant flow rate decreases proportionally.
