Installation and debugging of thermal expansion valve in refrigeration equipment

Installation and debugging of thermal expansion valve in refrigeration equipment

The correct installation of the thermal expansion valve will also affect the performance of the refrigeration device. Before installation, check whether the expansion valve is in good condition, especially the temperature sensing mechanism. Because the temperature sensing mechanism is filled with freon or other working medium, if there is leakage, the spring force will close the valve hole, and the expansion reading will not work. The installation position of the thermal expansion valve must be close to the evaporator, and the valve body should be placed vertically and cannot be installed tilted or reversed. During installation, care should be taken to keep the liquid in the temperature sensing mechanism in the temperature sensing bag at all times. Therefore, the bulb should be installed lower than the valve.

　　 Since the thermal expansion valve is operated by the temperature felt by the temperature sensor, the installation of the temperature sensor has a great influence on its performance. The temperature sensing bulb is installed on the air return pipe at the outlet of the evaporator. Generally, it should be more than 1.5m away from the suction port of the compressor, and installed in the horizontal pipe section as much as possible. But pay special attention, the bulb must not be placed in a place with fluid accumulation.

　　 If the evaporator outlet is equipped with a gas-liquid heat exchanger, the temperature sensing package is generally at the evaporator outlet, that is, before the heat exchanger. There are also temperature-sensing packaging on the return pipe behind the gas-liquid heat exchanger, but only when the heat provided by the high-temperature liquid refrigerant is sufficient to evaporate the refrigerant and overheat the gaseous refrigerant, this installation is allowed. And in this case, the thermal expansion valve should be adjusted to a very high operating superheat (not less than 12-20 ℃) to ensure that the freon evaporates and separates from the oil.

The installation method of the temperature sensing bulb is usually to place it on the return pipe of the evaporator, so that the temperature sensing bulb is close to the tube wall and wrapped tightly. The contact area should be cleaned of oxide scale. The natural color of the metal pipe should be exposed, and a layer can be applied if necessary. Lead paint is used as a protective layer to prevent rust. When the diameter of the return air pipe is less than 25mm, the temperature sensing bag can be tied on the top of the round air pipe. When the diameter of the return air pipe is larger than 25mm, the temperature sensing bag can be tied at 45° on the lower side of the return air pipe to prevent factors such as oil accumulation at the bottom of the pipe from affecting the correct temperature sensing of the temperature sensing bag.

　　 The debugging of the thermal expansion valve must be carried out under the normal operating state of the refrigeration device. If there is no thermometer at the outlet of the evaporator, the suction pressure of the compressor can be used as the saturation pressure in the evaporator to check the degree of superheat. However, due to the pressure drop of the suction pipe, the calculated superheat is higher than the actual superheat. If you feel that the degree of overheating is too small during adjustment, that is, the flow is too large, you can turn the adjusting rod in a clockwise direction by half a turn or a turn (that is, increase the spring force and decrease the valve opening) to reduce the flow, and vice versa. If you feel that the degree of overheating is too high, that is, the liquid supply is insufficient, you can turn the adjusting rod in the opposite direction to increase the flow. The whole adjustment process should be careful, and the number of turns of the adjusting rod screw should not be too many at a time (the joint rod screw rotates once, the superheat is about 1～20℃). After many adjustments patiently, until the requirements are met.

　　 For the thermal expansion valve, in addition to adjusting according to the measuring instrument, it can also be adjusted according to the empirical method. That is, turn the adjusting rod screw to change the opening of the valve, so that the outside of the return pipe of the evaporator can just be frosted or dew. For a refrigeration device with an evaporating temperature lower than 0°C, if you shake your hands after frosting, there will be a shady feeling of sticking your hands, indicating that the opening of the thermal expansion valve is appropriate. For the evaporation temperature at 0. For air-conditioning refrigeration devices above c, it can be judged based on condensation.