The refrigeration compressors can be classified according to the number of cylinder, compression method, drive type and motor location.
The refrigeration compressor compression method may be reciprocating centrifugal or rotary. The independent compressors are belt driven while the semihermetic compressors are direct drive
The reciprocating compressors have a piston in a cylinder. The piston acts as a pump to increase the pressure of the refrigerant from the low side to the high side of the system. A reciprocating compressor can have twelve or more cylinders.
The reciprocating compressors are commonly used on R-22 and R-134a refrigerant system. There are three types of reciprocating compressors: open drive, hermetic, and semihermetic.
Reciprocating compressors are typically used an internal multiple-step valve for the capacity control method. This method applies compressor oil pressure or high-side refrigerant pressure to a bellows or piston that actuates the unloader
Reciprocating compressors may also apply an external solenoid valve for each cylinder for the capacity control method. The solenoid valve allows compressor oil or high-side refrigerant to pass to the unloader.
A centrifugal compressor is basically a fan or blower that builds refrigerant pressure by forcing the gas through a funnel-shaped opening at high speed.
On centrifugal compressor, the vanes are opened and closed to control the compressor capacity. These vanes regulate the amount of refrigerant gas allowed to enter the fan or turbine. This method can limit the capacity by 10 to 25 percent.