Reference · Compressor types
Rotary Screw Air Compressors
Compressor type
5–500+ HP100–200 PSI
Rotary screw air compressors use two intermeshing helical rotors to compress air continuously, with no piston, no valves, no reciprocating mass. They are the dominant technology above ~10 HP in any application with sustained demand: continuous duty, lower vibration than reciprocating, longer service intervals, and (with variable-speed drives) the lowest cost per delivered SCFM at partial load. Oil-flooded screws are the volume market — oil seals the rotor clearances and absorbs the heat of compression. Oil-free screws (two-stage, dry rotors with timing gears) serve food, pharma, and electronics where downstream oil contamination is unacceptable. Representative families: Atlas Copco GA, Ingersoll Rand R-Series, Sullair LS/ShopTek, Kaeser SK/SM/ASD, Quincy QGS/QGV. Variable-speed drive (VSD) variants are standard above 50 HP and increasingly offered down to 15 HP.
How it works
Two intermeshing helical rotors (male + female) inside a precision-bored housing. Air is trapped between the rotors and the housing wall, then progressively compressed as the rotors turn. Oil-flooded designs inject lubricating oil into the air-end (sealing + cooling + lubrication); the oil is then separated downstream and recirculated. Oil-free designs use timing gears to keep the rotors out of contact and rely on tight tolerances + downstream cooling.
When to choose this type
Choose rotary screw when duty cycle exceeds ~50% sustained, when noise must stay below 75 dB without enclosure work, or when operating cost over a 10-year horizon dominates capital cost. VSD models are essentially mandatory if peak demand is >2× average demand. Choose oil-free if even trace oil contamination is unacceptable downstream.
Who buys these
- manufacturing plants with continuous air demand
- auto-body shops above 3 bays / 50% duty
- food and beverage processing
- pharmaceutical and medical device manufacturing
- electronics fabrication and clean rooms
Representative brands
Atlas Copco · Ingersoll Rand · Sullair · Kaeser · Quincy · Gardner Denver · Hitachi · ELGi · Mattei
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