Twin-screw type supercharger

A rotary-screw compressor is a type of gas compressor that uses a rotary-type positive-displacement mechanism. They are commonly used to replace piston compressors where large volumes of high-pressure air are needed, either for large industrial applications or to operate high-power air tools such as jackhammers.

The gas compression process of a rotary screw is a continuous sweeping motion, so there is very little pulsation or surging of flow, as occurs with piston compressors.

Rotary-screw compressors use two meshing helical screws, known as rotors, to compress the gas. In a dry-running rotary-screw compressor, timing gears ensure that the male and female rotors maintain precise alignment. In an oil-flooded rotary-screw compressor, lubricating oil bridges the space between the rotors, both providing a hydraulic seal and transferring mechanical energy between the driving and driven rotor. Gas enters at the suction side and moves through the threads as the screws rotate. The meshing rotors force the gas through the compressor, and the gas exits at the end of the screws.

The effectiveness of this mechanism is dependent on precisely fitting clearances between the helical rotors and between the rotors and the chamber for sealing of the compression cavities. However, some leakage is inevitable, and high rotational speeds must be used to minimize the ratio of leakage flow rate over effective flow rate.

In contrast to Roots blowers, screw compressors are made with different profiles on the two rotors: the male rotor has convex lobes which mesh with the concave cavities of the female rotor. Usually the male rotor has fewer lobes than the female rotor, so that it rotates faster. Originally, screw compressors were made with symmetrical rotor cavity profiles, but modern versions use asymmetrical rotors, with the exact rotor designs being the subject of patents.

Rotary-screw compressors tend to be compact and smoothly running with limited vibration, thus not requiring spring suspension. Many rotary-screw compressors are, however, mounted using rubber vibration-isolating mounts to absorb high-frequency vibrations, especially in rotary-screw compressors that operate at high rotational speeds. Rotary-screw compressors are produced in sizes that range in pumping speeds from 10 cubic feet per minute to several thousand CFM. Rotary-screw compressors are typically used in applications requiring more airflow than is produced by small reciprocating compressors but less than is produced by centrifugal compressors.

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Wikipedia