Reciprocating compressors
In this type of compressor, the pistons are designed in similar fashion to those used in a car engine: they slide inside a cylinder, drawing in and compressing the gas refrigerant. Each cylinder features a suction valve for the gas refrigerant and a delivery valve through which the gas refrigerant is sent to the condenser after having been compressed.
Reciprocating compressors are defined as open-type when one end of the crankshaft protrudes outside of the crankcase (the casing that contains the pistons and the mechanisms inside the compressor). In semi-hermetic compressors, on the other hand, both the compressor itself and the drive motor are housed inside the casing, which is designed so as to be opened for inspection and maintenance. In this case, the drive shaft and the crankshaft are one single piece. Semi-hermetic compressors are made so as to prevent air or dust from entering the mechanisms.
Reciprocating compressors are defined as hermetic when the casing is welded closed and sealed, and the heads of the cylinders cannot be accessed for inspection or maintenance. These are used in household refrigerators and freezers and in medium-capacity air-conditioning units.