What to do if the compressor returns liquid continuously?

As one of the serious problems in the operation of the compressor in the refrigeration system, the continuous return liquid is caused by the refrigerant flowing back to the compressor in the form of liquid and mixing with the lubricating oil When the lubricating oil is diluted to a low enough level, the bearing can not be fully lubricated, resulting in increased wear, which will lead to increased current, noise and vibration of the compressor, resulting in damage of the Zui final compressor When the compressor returns liquid continuously, the compressor body will light a red light At this time, the diagnosis and treatment method of "hope, test, check, and doctor" will come into use The first step is to look at the body and examine the symptoms to determine whether the compressor is suffering from a continuous fluid return First, it is necessary to observe the compressor from the outside to see if there is a large area of condensation or frosting of the compressor housing, or the large backlog of the foam of the oil mirror If these two symptoms occur, the compressor may suffer from continuous return fluid, which needs further inspection Step two: test the body, confirm the disease When the compressor appears above symptoms, it is necessary to check immediately, confirm the continuous return liquid disease: a compressor is measured to absorb the superheat degree: the measuring point is placed at the distance from the suction valve 152mm The minimum value of suction superheat * Zui of compressor in low temperature application system is 11K; the minimum value of suction superheat * Zui of compressor in medium and high temperature application system is 3-6k Second, measure the temperature difference between the oil tank and the suction pipe of the compressor: measure the temperature of the oil tank: theoretically, it is recommended to arrange a thermocouple at the center of the bottom of the compressor (non edge position) and keep it warm, but in actual operation, the measurement of the bottom center is often difficult, and the measurement position can be replaced by the bottom of the shell opposite the air return port It is recommended that the small value of temperature difference Zui for stable operation of compressor is 27 ℃ If the two measured values are too low at the same time, the probability of compressor suffering from continuous reflux disease is more than 90% If you want to make a diagnosis, you can measure the exhaust temperature again If the exhaust temperature is too low (the exhaust superheat * is lower than 25K, it is generally considered that the exhaust temperature is low), the compressor can make a diagnosis of continuous return fluid Note: * suction superheat = suction temperature - suction pressure corresponding to saturation temperature * exhaust superheat = exhaust temperature - exhaust pressure corresponding to saturation temperature diagnostic method step 3: check key points and confirm the source of the disease The medicine can only be dispensed if the symptoms are correct First, find out the cause of the continuous liquid return of the compressor in the refrigeration system, mainly including the following points (common causes have been marked with): ★ improper selection or use of the expansion valve: the selection of the expansion valve is too large or the commissioning is too large, and the refrigerant entering the evaporator is greater than the quantity that the evaporator can evaporate The expansion valve temperature sensing package is not insulated or not well insulated, the installation position is not right or even not installed, resulting in the detected superheat degree greater than the actual superheat degree, the expansion valve opening is too large, the evaporator is improperly configured or used: ★ the defrosting is not allowed or the defrosting interval is too long, especially the evaporation area of the heat exchange difference is small due to the excessive frosting of the exhaust system (steel or aluminum exhaust) Too much refrigerant filling, too small volume of gas-liquid separator or too large diameter of gas separation oil return hole: too small gas separation volume can't store too much refrigerant, too high liquid level, too high internal copper pipe of gas separation causes too large return oil return hole, resulting in a large number of refrigerant entering the compressor