Thermal expansion valve working principle, installation and commissioning

Thermal expansion valve working principle, installation and commissioning

1, thermal expansion valve introduction
Thermal expansion valve is an important control component in the refrigeration system, which is mainly used to control the rate of refrigerant from high pressure liquid to low pressure gas, so as to regulate the flow of refrigerant into the evaporator. This process is critical to maintaining optimal cooling on the evaporator coils and the overall energy efficiency of the system. The operating principle of the thermal expansion valve is based on several key factors: Superheat control: The thermal expansion valve controls the flow of refrigerant by monitoring the superheat of the refrigerant steam at the outlet of the evaporator (that is, the part of the temperature above the saturation temperature corresponding to its pressure). The control of the superheat ensures that the refrigerant in the evaporator evaporates completely, preventing the liquid refrigerant from entering the compressor and preventing "liquid shock". Pressure regulation: Thermal expansion valves also promote evaporation by reducing the pressure of the refrigerant, which is one of the key steps in the refrigeration cycle. This reduction in pressure causes the refrigerant to boil and absorb heat from the surrounding environment, thus achieving a cooling effect. Flow control: According to the heat load requirements of the evaporator, the thermal expansion valve dynamically adjusts the refrigerant flow. Under low load conditions, it allows less refrigerant to pass through; Under high load conditions, it allows more refrigerant to pass through. The thermal expansion valve structure usually includes a diaphragm, a temperature envelope (sensitive element to sense superheat), a spring (to provide closing force), and an adjustable control device. The refrigerant or oil in the temperature envelope expands or contracts due to the temperature change at the evaporator outlet, thereby changing the position of the diaphragm and controlling the opening degree of the valve.

2, thermal expansion valve MOP is what
The MOP function of the thermal expansion valve refers to the maximum operating pressure. This function is designed to protect the compressor in the refrigeration system from suction pressure exceeding the safe range. During the operation of the refrigeration system, the MOP function prevents the evaporator pressure from rising abnormally, thereby protecting the compressor from the damage caused by excessive suction pressure. In other words, MOP protects compressors and other components from overpressure by limiting the maximum working pressure of the refrigeration system, ensuring that the refrigeration system can operate in safe and stable conditions
In thermal expansion valves without MOP function, most of the medium charged in the temperature sensing bag exists in the form of liquid. When the temperature sensing bag is heated or cooled by the suction pipe of the compressor, the internal media will evaporate into gas or condense back to liquid accordingly, resulting in pressure changes, which affects the opening of the expansion valve and regulates the flow of refrigerant

3, expansion valve installation
The expansion valve must be installed in the liquid line located in front of the evaporator, and its temperature envelope should be fixed as close as possible to the suction line of the evaporator. If there is an external pressure balance, the balance pipe must be connected to the suction pipe immediately after the temperature packet.
Because the oil at the bottom of the line may produce an error signal, the thermal packet should never be located at the bottom of the suction tube, nor should the thermal packet be installed behind the heat exchanger, where it will send an error signal to the expansion valve. The warm packet must also not be installed near the large mass components, as this can also cause an error signal to be sent to the expansion valve.
As mentioned above, the temperature packet must be installed to the horizontal part of the suction line immediately after passing through the evaporator. The temperature packet must not be installed on the collection pipe or riser pipe behind the oil storage tank.

4. Adjust the expansion valve
The factory Settings of the expansion valve can meet the requirements of most applications, and the factory static superheat is generally set to 4 ° C. Turn the adjusting rod clockwise (turn it down), the static superheat of the valve increases, and turn the adjusting rod counterclockwise (turn it up), the static superheat of the valve decreases. Generally speaking, the adjusting rod rotates once, and the static superheat changes by 1~2 ° C. If the overheating in the evaporator is too high, the cause may be an insufficient supply of liquid refrigerant. Gradually turn the expansion valve setting rod counterclockwise until fluctuations are observed to reduce superheat. For the selection of expansion valve and the specific adjustment method of this article is not repeated, before we refrigeration encyclopedia sent but many articles, interested partners can see.

Shanghai KUB Refrigeration Equipment Co., Ltd.

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