In reality, rotary compressors are of four general design configurations: (i) rolling piston, (ii) rotating vane, (iii) screw, and (iv) scroll. Therefore, rotary compressors have a rotary or circular motion instead of a reciprocating motion. They operate on rotors which rotate on an eccentric shaft. Gas enters through a space between the rotor and the cylinder through a suction port. The gas is compressed as the rotor revolves due to the eccentrical assembly of the rotor and the cylinder. A discharge port on the opposite releases the compressed air. The two more commonly used rotary compressors include the rolling piston-type and the rotating-vane-type. Both are very similar in size, performance and applications. Rotary compressors are popular in domestic refrigeration and suited for applications where large volumes of vapor are circulated and where a low compression ratio is desired. In fact, these work as positive displacement pumps.
In a rotary compressor the rotor turns in a cavity. The refrigerant gas enters through a port, is compressed by the movement of the rotor after the rotor seals the port, and is moved to the discharge port. This is known as the basic rotary principle and applies to both vane and screw compressors.