Refrigerating System – Accumulators
It is well known that compressors are designed to compress vapors, not liquids. Many refrigeration systems are subject to the return of excessive quantities of liquid refrigerant to the compressor. Liquid refrigerant returning to the compressor dilutes the oil, washes out the bearings, and in some cases causes complete loss of oil in the compressor crankcase. This condition is known as oil pumping or slugging and results in broken valve reeds, pistons, rods, crankshafts, and the like. The purpose of the accumulator is to act as a reservoir to temporarily hold the excess oil-refrigerant mixture and to return it at a rate that the compressor can safely handle. Some accumulators include a heat-exchanger coil to aid in boiling off the liquid refrigerant while subcooling the refrigerant in the liquid line (see Figure 3.24), thus helping the system to operate more efficiently. Note that proper installation of a suction accumulator in the suction line just after the reversing valve and before the compressor helps eliminate the possible damage.
In large holdover plate refrigerator and freezer systems, refrigerant can accumulate in the plates and suction line when the compressor is not running. On start-up, this liquid refrigerant can be suddenly dumped into the compressor, creating a situation due to the liquid slugging of refrigerant and oil. This can cause damage to the compressor. When installed in the suction line of the compressor, a suction accumulator protects the compressor from this liquid slugging by gradually feeding liquid refrigerant into the compressor.
Note that accumulators should be selected according to the tonnage, evaporator temperature and holding capacity.