A great majority of reciprocating compressors which compress the refrigerant gas only on the forward stroke of a piston are built to be single acting in a large capacity range, up to hundreds of kilowatts. Models of these compressors may be single-cylinder or multicylinder in V (Figure 3.7), W, radial, or line form. The power required for the compressor can be provided either directly by a motor or indirectly by a belt or a gear drive. In these compressors, cylinder clearance volume, compression ratio, amount of suction superheat, valve pressure drops, and the refrigerant-oil characteristics are the main parameters which affect their efficiencies. The selection of cooling method is dependent on the discharge temperature. For example, when the discharge temperature is low, as in R-134a compressors, air cooling is usually chosen. Water cooling is used where high discharge temperatures occur.
Note that Danfoss Maneurop hermetic reciprocating compressors are specially designed for applications with a wide range of operating conditions. The concept has proven its reliability and durability in low, medium and high temperature applications. Suction gas enters the compressor and cools the electrical motor. The circular valve design and profiled piston provide for an efficient compression process. Discharge gas passes through an internal muffler to eliminate gas pulsation which reduces sound level and vibration. The internal discharge line runs through the oil sump taking care of an oil temperature high enough to evaporate eventual liquid refrigerant entering the compressor.