Adjustment skill and maintenance operation of thermal expansion valve

1 The adjustment skill and taboo of the thermal expansion valve should be adjusted when the refrigeration system is debugged in order to ensure that the thermal expansion valve can correctly perform the automatic adjustment in the operation of the system The adjustment of thermal expansion valve is realized by adjusting rod In essence, the turning out of the regulating rod is to compress or loosen the spring, that is, to adjust the static assembly superheat of the thermal expansion valve to meet the needs of refrigeration conditions Generally speaking, forward rotation means forward rotation and backward rotation means backward rotation When the evaporation pressure is to be adjusted, the cap can be removed, and the adjusting rod can be rotated with a wrench to increase the compression of the spring, force the diaphragm to move up and close the valve, and the evaporation pressure will gradually decrease In the same way, the counter rotating regulating rod will open a large valve and increase the evaporation pressure When adjusting the thermal expansion valve, a low-pressure gauge shall be installed on the suction stop valve of the compressor to observe the change of evaporation pressure The normal evaporation pressure is frosting or condensation to the suction pipe (frosting of medium and low temperature equipment; condensation of air conditioning equipment) If the white frost or condensation is connected to the suction stop valve or even half of the compressor, it means that the valve is too large and should be reduced If the white frost or condensation is only connected to the outlet of the evaporator or cannot be connected to the outlet, it means that the valve is too small and should be increased The commissioning of thermal expansion valve can be generally carried out in two steps The beginning is coarse adjustment, that is, each adjustment can be rotated about a circle When the equipment is close to its operating condition, it shall be carefully adjusted, rotating 1 / 4 ~ 1 / 2 circle each time After each adjustment, make the system run for several minutes or more, observe the change of low-pressure meter, and then decide the next adjustment At the end of expansion valve commissioning, the cap shall be screwed on and spanned tightly to prevent refrigerant leakage Adjusting the thermostatic expansion valve is a meticulous work, and we must not be impatient in the adjustment process The adjusted thermal expansion valve shall not be adjusted for other reasons, unless the operation condition of the refrigerator is changed Generally, the thermal expansion valve of the unit leaving the factory has been adjusted before leaving the factory, and the unit should not be adjusted during the field commissioning 2 Maintenance and operation of thermal expansion valve common faults of thermal expansion valve include blockage, leakage of working medium injected into temperature sensing bag, etc (1) there are two situations of valve hole blockage: ice blockage and oil blockage If there is water in the refrigeration system, it will be dissolved in the refrigerant The amount of its dissolution is related to the temperature of the refrigerant If the temperature is higher, the amount of its dissolution will be larger, and if the temperature is lower, the amount of its dissolution will be smaller When the refrigerant liquid with a condensation temperature of about 30t flows into the expansion valve orifice for throttling, it will immediately cool down to the saturation temperature (evaporation temperature) under the evaporation pressure Part of the water will be separated out If the evaporation temperature of the part attached to the valve orifice is below 0 ℃, it will form an ice layer When the ice layer increases, the valve orifice will be blocked Refrigerator oil and refrigerant will also dissolve each other, and the amount of its dissolution is also related to temperature High temperature dissolves more, low temperature dissolves less When the liquid bursts into the expansion valve orifice and its temperature drops rapidly after throttling, part of the refrigerant oil is separated and stuck around the valve orifice When the evaporation temperature is lower than the freezing point of the refrigerant oil, the refrigerant oil will condense into paste shape When the oil gradually increases, the valve orifice will be blocked because the lower the evaporation temperature is, the easier the water and oil will be separated, so the ice blockage and oil blockage are easy to evaporate Occurs in low temperature refrigeration equipment 1) judgment of ice block or oil block in valve hole When the refrigeration unit starts to operate normally after a period of operation, the suction pressure drops rapidly to the negative pressure (vacuum), the temperature of the warehouse (room) rises, the frost layer melts (first of all, the frost layer of the suction pipe melts), and the flow sound of the expansion valve cannot be heard on the side ear At this time, it can be judged that the valve hole is blocked by ice or oil In order to further verify that the valve hole is blocked, the expansion valve body can be heated with alcohol lamp (no need to stop) After heating for one or two minutes, if you hear After that, the squeak can be heard, and the suction pressure also rises The outlet of the expansion valve begins to form a white letter, indicating that the valve hole is indeed blocked by ice or oil 2) troubleshooting methods Replace the desiccant in the drying filter When there is much water in it, the reagent grade anhydrous calcium chloride can be used first, and then the silica gel can be replaced after one or two days of chilling pepper If there is no drying filter in the system, connect a drying filter temporarily (2) the filter screen at the inlet of the expansion valve is blocked The filter screen of the expansion valve is filled with impurities and dirt, so that the valve hole is not blocked When there are many impurities in the filter screen, the mesh is not smooth or even completely blocked The phenomenon is also suction month pull vacuum, reservoir (chamber) temperature does not drop, and half or the whole expansion valve knot white song listen to the expansion valve has weak squeak, squeak intermittent sound, which means that the filter screen is blocked When the wrench handle is used to tap the inlet joint of the valve, if the noise is louder than the original one, it is confirmed that most of the mesh holes of the filter screen are seriously blocked, and the air flow sound of the refrigerant in the valve can not be heard The valve body is also: generally, it is invalid to tap the outlet joint with the wrench handle But the filter screen is all blocked to less The obvious difference between filter screen blockage and valve hole blockage is that valve hole blockage is the one that operates normally during startup and operation, and filter screen blockage is the one that occurs when the unit starts to suck up or pull vacuum The phenomenon of insufficient refrigerant should be distinguished from that of clogged filter screen When the refrigeration unit is running, if you hear the hiss and hiss of the expansion valve, the sound is loud, the suction pressure is low, the suction pressure gauge point fluctuates, the temperature of the warehouse (room) is not low enough, some of the evaporation pipes are not frosted, and the refrigerant is insufficient, do not mistake for the failure of the expansion valve The way to remove the clogged filter screen is to remove the filter screen and clean it with gasoline (3) leakage of the working medium injected into the sensing mechanism when the tears are injected into the sensing mechanism, the sensing pressure of the temperature sensing package disappears, causing the valve to be closed The teardrop refrigeration unit pulls vacuum at the beginning of operation, the temperature in the warehouse (room) can not be lowered at all, and the expansion valve has no air flow sound Remove the expansion valve, remove the filter screen interface, and use the nozzle to suction the outlet connector of the expansion valve If the suction is not available, and the expansion valve can be hung with the lips, it means that the valve hole is not available at all It is true that the valve cannot be closed, so the expansion valve of the same model should be replaced.