Thermal expansion valve adjustment skills and maintenance operation methods

Thermal expansion valve adjustment skills and maintenance operation methods

1. Adjustment skills and taboos of thermal expansion valve

　　 In order for the thermal expansion valve to perform the automatic adjustment function under one of the working conditions, it must be adjusted during the commissioning of the refrigeration system, so as to ensure that the thermal expansion valve can correctly perform automatic adjustment during system operation.

　　The adjustment of the thermal expansion valve is realized by adjusting the lever. Spinning or unscrewing the adjusting rod is essentially compressing or relaxing the spring, that is, adjusting the superheat degree of the static assembly of the thermal expansion valve to meet the needs of cooling conditions. Generally, forward rotation is forward, and reverse rotation is backward. When you want to adjust the evaporation pressure, you can remove the cap and use a wrench to turn the adjustment rod forward to increase the compression of the spring, forcing the diaphragm to move up and closing the valve, and the evaporation pressure will gradually drop. In the same way, the reverse rotation of the regulating rod will open the valve and increase the evaporation pressure.

　　 When adjusting the thermal expansion valve, a low pressure gauge should be installed on the compressor suction shut-off valve to observe the change of evaporation pressure. The normal evaporation pressure is hoarfrost or condensation to the suction pipe (hoarfrost on medium and low temperature equipment; condensation on air conditioning equipment). If hoarfrost or condensation condenses on the suction shut-off valve, or even half of the compressor, the valve is too large and should be adjusted smaller. If hoarfrost or condensation only condenses on the evaporator outlet or does not condense on the outlet end, the valve If it is too small, it should be adjusted larger.

　　 The debugging of thermal expansion valve can generally be carried out in two steps. The beginning is coarse adjustment, that is, it can be rotated about one circle each time it is adjusted. When the equipment is close to its operating conditions, fine adjustments should be made, with 1/4 to 1/2 rotations each time. After each adjustment, let the system run for several minutes or ten minutes, and observe the changes of the low-pressure meter, and then decide the next adjustment. When the adjustment of the expansion valve is finished, the cap should be screwed on and tightened with a wrench to prevent refrigerant leakage.

　　Adjusting the thermal expansion valve is a meticulous job, and you should not be impatient during the adjustment process. The adjusted thermal expansion valve shall not be adjusted for other reasons unless the refrigerator changes its operating conditions. Generally, the thermal expansion valve of the unit that is shipped from the factory has been adjusted before leaving the factory, and should not be adjusted when the unit is commissioned on site.

Thermal expansion valve adjustment skills and maintenance methods

　　 2. Overhaul operation of thermal expansion valve

　　 The common faults of the thermal expansion valve include blockage, leakage of the working fluid filled in the bulb, etc.

　　1. Valve hole blockage. Valve hole blockage has two situations: ice blockage and oil blockage. If there is water in the refrigeration system, it will dissolve in the refrigerant, and its dissolution amount is related to the temperature of the refrigerant. The higher the temperature, the larger the dissolution, and the lower the temperature, the smaller the dissolution. When the refrigerant liquid with a condensing temperature of about 30t flows into the expansion valve orifice throttling, it is immediately cooled to the saturation temperature (evaporation temperature) under the evaporation pressure, and a part of the water is precipitated. If the evaporation temperature is below 0 ℃, it is attached to the valve hole. It will form an ice layer, and when the ice layer increases, the valve hole is blocked.

　　 Refrigerator oil and refrigerant will also dissolve each other, and the amount of dissolution is also related to the temperature. High temperature dissolves more, but low temperature dissolves less. When the liquid enters the expansion valve hole and its temperature drops rapidly after throttling, part of the refrigerating machine oil is separated and sticking around the valve hole. When the evaporation temperature is lower than the freezing point of the refrigerating machine oil, the refrigerating machine oil will condense into a paste. As the oil gradually increases, the valve holes are blocked because the lower the evaporation temperature, the easier it is for water and oil to separate. Therefore, ice blockage and oil blockage are likely to occur in low-temperature refrigeration equipment with lower evaporation temperatures.

　　 1) Judgment of ice blockage or oil blockage in valve hole. When the refrigeration unit starts to operate normally after a period of operation, the suction pressure drops rapidly to negative pressure (vacuum), the temperature of the storage (chamber) rises, and the frost layer melts (first is the frost layer of the suction pipe). Sound of flow to the expansion valve. At this time, it can be basically judged that the valve hole is blocked by ice or oil. In order to further confirm that the valve hole is blocked, use an alcohol lamp to heat the expansion valve body (no need to stop). After heating for one or two minutes, if you hear the sound of airflow, then you can hear the squeaking sound, and the suction pressure also rises , The outlet of the expansion valve begins to form white again, indicating that the valve hole is indeed blocked by ice or oil.

　　 2) Methods of troubleshooting. Replace the desiccant in the filter drier. When there is a lot of water in the medium, use reagent-grade anhydrous calcium chloride first, and then replace the silica gel after cooling the pepper for one or two days. If there is no filter drier in the system, a filter drier can be temporarily connected.

　2. The inlet filter of the expansion valve is blocked. The filter of the expansion valve is overloaded with impurities and dirt, so that the valve hole will not be blocked. When there are too many impurities in the filter, the mesh will not be smooth or even completely blocked. The phenomenon is also that the vacuum is pulled by the inhalation month, the temperature of the library (room) does not drop, and half or the entire expansion valve is white. The expansion valve has a faint squeaking and intermittent sound, which indicates that the filter is not smooth and all blocked. . When tapping the inlet connector of the valve with a wrench handle, if you hear a sound that is louder than the original sound, it is confirmed that most of the mesh of the filter is clogged and blocked. The situation is that the air flow of the refrigerant in the valve cannot be heard. Body: Generally, it is invalid to tap the joint with a wrench handle. However, all the filters are clogged to less.

　　 The obvious difference between clogged filter and clogged valve hole is: the valve hole is clogged when the unit is running normally within the time of startup, and the filter screen is clogged if the unit starts to suck up or pull the vacuum. The phenomenon that occurs when the refrigerant is insufficient and the phenomenon when the filter is blocked should be distinguished when judging. When the refrigeration unit is running, if you hear a hissing sound from the expansion valve, louder noise, low suction pressure, fluctuations in suction pressure gauge, and storage (room) temperature not low enough, part of the evaporator tube does not form frost , Don’t mistake the expansion valve for failure due to insufficient refrigerant. The way to eliminate the blockage of the filter is to remove the filter and clean it with gasoline.

　　3. Leakage of working fluid perfused in the sensing mechanism When tears leak in the sensing mechanism, the sensing pressure of the temperature sensing bulb disappears, causing the valve to close. The Tear refrigeration unit pulls the vacuum as soon as it starts to operate, the temperature in the storage (chamber) cannot drop at all, and there is no sound of airflow in the expansion valve. Remove the expansion valve, remove the filter interface, and suck the outlet joint of the expansion valve with your mouth. If the suction fails, and you can hang it with your lips, the valve hole is not open at all. It is true that the valve cannot be closed, and the expansion valve of the same model should be replaced.