Liquid Slugging is where extreme cases of Flooded Start or Liquid Flood Back occur. When large quantities of liquid refrigerant enter the compressor and then mix with the lubricating oil in the compressors sump. The resulting liquid/oil mixing and diluting, then creates major amounts of liquid and oil droplets in a frothy foam mixture.
During extreme cases, this foam/oil/liquid mixture can be carried into the suction gallery and then through the suction valves and into the cylinder. This “Wet” mix will wash the cylinder lubricant away and can also cause the valve reeds to break. Due to this liquid/oil mixture carrying non compressible particles this can cause the valve plate to deflect to the point where it breaks. The Suction valve plate will show small dents or even holes through the plate. The valve plate then falls into the cylinder and on to the piston crown. As the piston travels up to the top of the cylinder during the compression cycle the valve plate is then smashed up into the discharge valve plate. This can cause a hole to be punched through the piston crown and damage to the discharge valve assembly occurs as there is almost no clearance between the top of the piston crown and the discharge valve, which gives the compressor its high efficiency rating. The discharge valve assembly can also be completely smashed to pieces in certain instances.
In very extreme cases of slugging, the cylinder can be virtually filled with liquid and can cause con rod breakages and even broken crankshafts have been the result of hydraulic lock in the cylinder. This is more in Flooded Start/Slugging instances.
Compressors are designed to pump refrigerant in its vapour form only, NOT LIQUID!
The action of the compressor is: