Do you know the refrigeration compressor liquid blow
Liquid shock refers to the situation where the refrigerant fails to absorb heat or evaporates sufficiently, and the refrigerant liquid or wet steam is sucked into the compressor by the compressor. It is called liquid shock. 1. The main causes are: 1. Liquid return: Incomplete refrigerant evaporation: liquid return is closely related to the selection and use of expansion valves. Expansion valve selection is too large, the superheat setting is too small, the temperature sensor installation method is incorrect or the insulation bandage is damaged, the expansion valve failure may cause liquid return. 2. There is too much foam when starting with liquid: When the return air-cooled compressor starts, the phenomenon that the lubricating oil in the crankcase violently foams is called starting with liquid. The basic reason for starting with liquid is that there is a large amount of refrigerant dissolved in the lubricating oil and sinking under the lubricating oil. It suddenly boils when the pressure drops suddenly, and causes the foaming phenomenon of the lubricating oil. The liquid blow caused by the starting with liquid only occurs During the startup process. 3. There is too much lubricating oil in the compressor: the oil level is too high. The high-speed rotating crankshaft and connecting rod head may frequently hit the oil surface, causing a large amount of lubricant splashing. Once the splashed lubricating oil enters the intake duct and is brought into the cylinder, it may cause liquid shock. 4. Too much additional refrigerant: Too much refrigerant will not only cause the compressor to return air with liquid, but also may cause the refrigerant flow rate in the compressor return pipe to be too low, and the lubricating oil in the evaporator cannot return to the compressor, causing compression The machine runs out of oil. 5. Evaporator failure: enter the compressor air return pipe without evaporating in the evaporator, which is easy to cause compressor liquid blow. If the evaporator fails to cause serious frosting on the coil, incomplete refrigerant evaporation is also the main reason for the compressor to return air and liquid. 6. The volume design of the gas-liquid separator is unreasonable: adding a gas-liquid separator to the system is the most effective way to prevent compressor oil shortage and liquid blow. The gas-liquid separator can temporarily store excess refrigerant in the gas-liquid separation. In the heat pump system, the refrigerant liquid accumulated in the condenser can be transferred to the gas-liquid separator when the hot gas defrosting cooling and heating switch work, which greatly reduces the risk of liquid shock. 7. Refrigerant migration: Refrigerant migration means that when the compressor stops running, the refrigerant in the evaporator enters the compressor in gas form through the return line and is absorbed by the lubricating oil, or condensed in the compressor with the lubricating oil. The process or phenomenon of mixing. 2. What harm will liquid strike cause: For the piston machine: It causes a large number of bubbles in the lubricating oil, destroys the oil film on the lubricating surface, and makes the oil pressure unstable; causes the moving parts to operate without good lubrication, causing the hair to hold the shaft; causes the cylinder liner to cool and shrink sharply, holding the piston; when serious Damage to the cylinder liner, piston, connecting rod, piston pin, etc. For screw machine: The liquid shock can cause vibration, increase noise, and damage the rotor and bearings (excessive force); severe liquid shock can also damage the equipment and cause accidents. To scroll compressor: The liquid hammer produces the greatest impulse to the scroll, which may break the scroll. The lubricating oil containing a large amount of liquid refrigerant has a low viscosity and cannot form a sufficient oil film on the friction surface, resulting in rapid wear of the moving parts in the compressor; The refrigerant will boil when encountering heat during transportation, which will affect the normal transportation of lubricating oil. 3. How to deal with liquid strike: In the event of liquid shock, immediately close the compressor suction shut-off valve, and close the throttle valve to stop the liquid supply. If the suction temperature continues to decrease, continue to close or even close the suction valve. The frictional heat between the crankshaft and the bearing bush is used to evaporate the refrigerant in the crankcase until the refrigerant in the crankcase is completely evaporated. After that, slightly open the suction shut-off valve and slowly increase the load. When liquid hammer occurs, pay attention to observe and adjust the oil pressure. If there is no oil pressure or the oil pressure is too low, stop the machine immediately, release the lubricating oil and refrigerant in the crankcase, and refuel and start the machine. Four. How to prevent the compressor from hydraulic shock: 1. Reducing the refrigerant charge: The best way to protect the compressor from failure caused by liquid refrigerant is to limit the refrigerant charge to within the compressor's allowable range. If this is not possible, the charging volume should be reduced as much as possible under the condition of ensuring the cooling effect. The bubbles in the sight glass due to the small diameter of the liquid tube and the low pressure head should be alert and reasonably charged. Refrigerant injection is very important. 2. Crankcase heater: The function of the crankcase heater is to keep the temperature of the refrigerating oil in the crankcase higher than the temperature of the compressor suction inlet in the system. The crankcase heater is generally continuously heated during use. The crankcase heater is very effective to prevent migration, but the crankcase heater cannot protect the compressor from damage caused by the liquid reflux, and the heater must be turned on when the compressor is turned on. It was warmed up for a long time before and was not operable for practical applications. 3. Overheating heater for return air pipe: In cold seasons, there is still the possibility of return air with liquid when the compressor is running. In this way, an electric heater or hot air can be added to the return air pipe section of the compressor to increase the superheat of the return air of the compressor. The method is simple and effective, and an overheat detection device can be added to make the control more accurate, thereby protecting the compressor and preventing liquid shock. 4. Suction pipe gas-liquid separator: Install a gas-liquid separator on the suction pipe to temporarily store the overflowing liquid refrigerant in the system and return the liquid refrigerant to the compressor at a rate that the compressor can withstand. Because different refrigeration systems have different overall charging requirements and different refrigerant control methods, whether or not a gas-liquid separator is required and how large a gas-liquid separator is required depends largely on the requirements of the specific system. In addition, controlling the opening of the throttling element and increasing the heat exchange area of the evaporator during the design phase of the refrigeration system can effectively increase the return air superheat and reduce the occurrence of compressor liquid hammer during system operation. When charging refrigerant, avoid liquid charging from the low pressure side to prevent the compressor from starting with liquid. Liquid blow refers to the situation where the refrigerant fails to absorb heat or evaporates sufficiently, and the refrigerant liquid or wet steam is sucked into the compressor by the compressor. It is called liquid blow.
