Morning Sun HVAC design mini program
1. Adjustment skills and taboos of thermal expansion valve
In order for the thermostatic expansion valve to perform automatic adjustment function under one of its working conditions, it must be adjusted when the refrigeration system is debugged, so as to ensure that the thermostatic expansion valve can correctly perform automatic regulation during system operation. The adjustment of the thermostatic expansion valve is achieved by means of a regulating rod. The rotation or rotation of the adjustment lever is essentially the compression or relaxation of the spring, that is, the adjustment of the static assembly superheat of the thermostatic expansion valve to meet the needs of the refrigeration condition. Generally, the rotation is forward, and the reverse rotation is retreat. When the evaporation pressure is to be adjusted, the cap cover can be removed, and the adjustment lever can be rotated with a wrench to increase the compression of the spring, forcing the diaphragm to move up and close the small valve, and the evaporation pressure will gradually decrease. Similarly, the anti-spin adjustment lever opens a large valve to increase the evaporation pressure.
When adjusting the thermostatic 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 white frost or condensation to the suction pipe (medium and low temperature equipment white frost; Condensation of air conditioning equipment). If the white frost or condensation is condensed to the suction shut-off valve, or even half of the compressor, the valve is too large, it should be adjusted smaller, if the white frost or condensation only settles to the evaporator outlet or the junction can not reach the outlet end, indicating that the valve is too small, it should be adjusted larger.
The commissioning of thermostatic expansion valve can generally be carried out in two steps. It starts with a coarse tone, which means that it can be rotated about one turn each time it is adjusted. When the equipment is close to its operating conditions, it should be fine-tuned, and each rotation is 1/4 to 1/2 turns. After each adjustment, the system should be operated for a few minutes or ten minutes, and observe the changes in the low pressure gauge before deciding on the next adjustment. At the end of the expansion valve commissioning, the cap should be screwed up and tightened with a wrench to prevent refrigerant leakage. Adjusting the thermostatic expansion valve is a meticulous task, and it is important not to be in a hurry during the adjustment process. The adjusted thermostatic expansion valve must not be adjusted for other reasons unless the chiller changes its operating conditions. In general, the whole machine is out of the factory, the thermal expansion valve has been adjusted before leaving the factory, and the unit should not be adjusted when debugging on site.
2. Maintenance operation of thermal expansion valve
The common faults of thermostatic expansion valve are blockage, temperature sensing package working fluid leakage, etc., and the valve hole is blocked by ice blockage and oil blockage.
If the refrigeration system contains moisture, it will be dissolved in the refrigerant, and its dissolution amount is related to the temperature of the refrigerant, the high temperature and its dissolution amount are large, and the low temperature dissolution amount is small. When the refrigerant liquid with a condensation temperature of about 30t flows into the expansion valve hole and is throttled, it is immediately cooled down to the saturation temperature (evaporation temperature) under the evaporation pressure, and part of the water is precipitated, and if the evaporation temperature of the valve hole is below 0 °C, it will form an ice layer, and when the ice layer increases, the valve hole is blocked.
Refrigeration oil and refrigerant will also dissolve each other, and its dissolution amount is also related to temperature, high temperature dissolution amount is large, low temperature dissolution amount is small. When the liquid bursts into the expansion valve hole after the throttling of its temperature drops sharply, part of the freezer oil is separated and stuck around the valve hole, when the evaporation temperature is lower than the freezing point of the refrigeration oil, the refrigeration oil will condense into a paste, when the oil gradually increases, the valve hole is blocked because the lower the evaporation temperature, the easier it is to separate the water and oil, so ice blockage and oil blockage are easy to occur in the low temperature refrigeration equipment with lower evaporation temperature.
Judgment of ice plugging or oil blockage of valve holes:
When the refrigeration unit starts to operate normally after a period of operation, the suction pressure drops sharply to negative pressure (vacuum), the temperature of the library (room) rises, the frost layer melts (first of all, the frost layer of the suction pipe melts), and the flow of the expansion valve cannot be heard in the side ear. 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, the expanded valve body can be heated with an alcohol lamp (without stopping), and after heating for one or two minutes, if you hear ... The sound of air flow, followed by the squeaking sound, the suction pressure also rose, and the outlet of the expansion valve began to white again, indicating that the valve hole was indeed blocked by ice or oil.
Troubleshooting methods:
Replace the desiccant in the filter drier. When there is more water in it, you can first use reagent-grade anhydrous calcium chloride, and then replace the silicone after a day or two of refrigeration pepper. If there is no filter drier in the system, a filter drier can be temporarily connected.
Expansion valve inlet filter clogging:
The filter screen of the expansion valve is over-hugged with impurities and dirt, so that the valve hole is not blocked. When there are more impurities in the filter, the mesh is not very smooth or even completely unblocked. Its phenomenon is also the suction moon pull vacuum, the temperature of the library (room) does not drop, and half or the entire expansion valve is white And the expansion valve has a weak squeaking intermittent sound, which indicates that the filter is not smooth and has all blockages. When tapping the inlet joint of the valve with the wrench handle, if the sound is heard louder than the original sound, it is confirmed that most of the mesh holes of the filter are blocked and blocked, and the air flow sound of the refrigerant in the valve cannot be heard, and the valve body is also: generally the wrench handle is ineffective. But the strainer is all blocked to less.
The obvious difference between filter screen clogging and valve hole clogging:
If the valve hole is blocked when the machine is running normally within the time of start-up operation, if the unit is sucked up or pulled at the beginning, the filter is blocked. The phenomenon that occurs when the refrigerant is insufficient should be distinguished from the phenomenon when the filter is blocked. When the refrigeration unit is running, if you hear the expansion valve has a booing sound, the sound is larger, the suction pressure is also low, the suction pressure meter point fluctuates, the library (room) temperature is not low enough, part of the evaporation tube does not have white frost, the lack of refrigerant, do not mistake the expansion valve failure. The way to eliminate the clogging of the filter is to remove the filter and wash it and bake it with gasoline.
Fluid leakage from perfusion in the induction mechanism:
When the tear leaks in the induction mechanism, the inductive pressure of the sensory temperature pack disappears, causing the valve to close and not open. The tear refrigeration unit pulled the vacuum at the beginning of operation, the temperature in the library (room) could not be reduced at all, and the expansion valve did not have a little air flow sound. Remove the expansion valve, remove the filter interface, and suck the outlet joint of the expansion valve with the mouth, if it cannot be sucked, and can be hung with the lips, indicating that the valve hole is not open at all. It is true that the valve does not open and should be replaced with the same type of expansion valve.
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