What is compressor liquid impact and what are the causes?

1, What is liquid impact?
Liquid impact is a possible malfunction in refrigeration systems, specifically referring to a series of problems caused when the refrigerant fails to evaporate sufficiently or enters the compressor in a liquid state under unexpected conditions. This situation can lead to undue liquid impact inside the compressor, causing serious damage to it. The occurrence of liquid impact is usually related to various factors such as the amount of refrigerant charged, the efficiency of the evaporator, and the defrosting effect of the system.
At the moment of startup, a large amount of refrigerant rushes in: If there is too much unevaporated refrigerant in the system at the moment of compressor startup, these liquid refrigerants will be sucked in as the compressor starts.
Insufficient evaporator flow: When the evaporator cannot effectively handle the amount of refrigerant passing through it, it may cause some refrigerant to return to the compressor before fully evaporating.
Incomplete defrosting: If the defrosting process fails to effectively remove the ice layer on the evaporator, residual liquid refrigerant will flow into the compressor after the temperature rises.
Improper operation of directional valve: When using a directional valve for directional operation, if the timing is not well controlled, it may cause the liquid in the evaporator to directly enter the compressor.
2, The impact of liquid impact on compressors
Liquid impact not only affects the normal operation of compressors, but also poses specific hazards to different types of compressors:
Vortex compressor: Liquid impact can exert a huge impact force on the vortex disc, which may cause it to break. In addition, lubricating oil containing refrigerants reduces viscosity and cannot form an effective oil film to protect moving parts from wear. Meanwhile, the boiling of refrigerant in lubricating oil can affect the lubrication effect and further exacerbate wear.
Screw compressor: Although screw compressors are more resistant to liquid impact compared to other types, they can still cause increased vibration and noise due to liquid impact, and even damage bearings and other important components.
Reciprocating compressor: The high pressure generated by liquid impact can quickly damage key components such as valve plates, pistons, connecting rods, etc. For this type of compressor, liquid impact is almost equivalent to a fatal blow.
3, How to prevent liquid impact
It is necessary to take the following measures to prevent damage to the compressor caused by liquid impact:
Reasonably control the refrigerant charging amount: Ensure that the refrigerant charging amount is within the recommended range of the compressor, and minimize unnecessary charging, especially avoiding liquid charging on the low-pressure side.
Installing a crankcase heater: By maintaining the oil temperature in the crankcase above the intake inlet temperature, the risk of refrigerant migration can be reduced, but this does not completely prevent the damage caused by the backflow of liquid refrigerant to the compressor.
Configure gas-liquid separator: The gas-liquid separator installed on the suction pipe can temporarily store excess liquid refrigerant and return it to the compressor at a safe speed, which is particularly important for large refrigeration systems.
Application of return air pipe overheating heating device: In cold environments, using an electric heater or other methods to increase the return air temperature ensures sufficient superheat and helps prevent liquid refrigerant from entering the compressor.
Optimize system design: Improve the design of throttling elements and the heat transfer area of the evaporator from the source to enhance the superheat of the return air and reduce the possibility of liquid impact.