In an inactive air conditioning or refrigeration system, refrigerant tends to condense and collect at low and/or cool locations in the system. Because of the affinity between refrigerants and the lubricants used therewith, refrigerant is normally present in the oil. If liquid refrigerant and/or oil is drawn into the compressor, a condition known as slugging occurs. Because liquids are essentially incompressible, the increased volume required to be discharged due to the incompressibility can cause damage to the compressor. This damage is due to the pressure build up caused by the higher than design volumetric flow due to the incompressibility of the liquid refrigerant and/or oil.
To avoid liquid slugging, a suction accumulator is commonly located immediately upstream of the suction of the compressor of an air conditioning or refrigeration system. The accumulator is normally limited in size for reasons of cost, available space, or as a matter of design choice. These limitations allow only a certain maximum oil/refrigerant ratio where the amount of oil is determined by the size of compressor oil sump and the amount of refrigerant is set by the charge amount which optimizes system performance. An accumulator serves two major purposes in that it acts as a sump for storing liquid refrigerant and any associated oil as well as serving to meter the feeding of the liquid refrigerant/oil back to the compressor. The suction feed pipe extends into the accumulator to a height above the design level of liquid refrigerant/oil and has a metered opening in fluid communication with the interior of the accumulator in a lower portion of the accumulator corresponding to a minimum residual liquid refrigerant/oil level.
When the compressor is started, the liquid which has entered and collected in the suction accumulator will tend to be drawn into the compressor with the liquid refrigerant tending to evaporate due to the reduced pressure associated with the suction stroke of the compressor. Normally, the liquid collecting in the accumulator in an inactive air conditioner will, primarily, be refrigerant and components relying on the normal oil content for lubrication may, instead, have lubricant washed away by refrigerant upon start up. Other than the initial liquid in the suction accumulator, gaseous and/or liquid refrigerant will be drawn from the evaporator into the accumulator and via the suction feed pipe into the compressor with the flow entering the suction feed pipe at a location in the upper portion of the accumulator. Additionally, any liquid in the accumulator at a level such as to be in fluid communication with the metered opening will be drawn into the suction flow on a metered basis with the liquid refrigerant tending to be evaporated in being aspirated into the suction flow. The metered flow into the suction feed pipe will continue until the liquid level is brought down to the level of the metered opening.