The effectiveness of this mechanism is dependent on close fitting clearances between the helical rotors and the chamber for sealing of the compression cavities.
Rotary screw compressors are used in a diverse range of applications. Typically, they are used to supply compressed air for general industrial applications. Trailer mounted diesel powered units are often seen at construction sites, and are used to power air operated construction machinery.
In an oil-flooded rotary screw compressor, oil is injected into the compression cavities to aid sealing and provide cooling sink for the gas charge. The oil is separated from the discharge stream, then cooled, filtered and recycled. It is usual for some entrained compressor oil to carry over into the compressed gas stream. In some applications, this is rectified by coalescer/filter vessels.
Standard oil-flooded compressors are capable of achieving output pressures over 200 psig, and output volumes of over 1500 cubic feet per minute (measured at 60 °C and atmospheric pressure).
In an oil-free compressor, the air is compressed entirely through the action of the screws, without the assistance of an oil seal. They usually have lower maximum discharge pressure capability as a result. However, multi-stage oil-free compressors, where the air is compressed by several sets of screws, can achieve pressures of over 150 psig, and output volume of over 2000 cubic feet per minute (measured at 60 °C and atmospheric pressure).
Oil-free compressors are used in applications where entrained oil carry-over is not acceptable, such as medicial research and semiconductor manufacturing.