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Rotary-lobe Compressors

At the heart of each of our custom packages lies an oil-free rotary-lobe compressor. The rotary-lobe compressor is a variant of rotary-type positive displacement compressor.

Rotary-lobe compressors are typically known as ‘roots-type blowers’ or ‘vacuum boosters’, according to the situation in which they are used:

  • Blower – Discharge pressure above atmospheric pressure
  • Vacuum Booster – Suction and discharge pressure below atmospheric pressure

Vacuum Booster

Principles of Operation

The rotary-lobe compressor incorporates two intermeshing rotors mounted on parallel shafts. In a twin-lobe compressor, each rotor has two lobes (four lobes per compressor). In a tri-lobe machine each rotor has three lobes (six lobes per compressor).

  • The two rotors rotate in opposite directions.
  • As each rotor passes the blower inlet, it traps a definite volume of gas (the ‘displaced volume’) and carries it around the case to the blower outlet. With constant speed operation, the displaced volume remains approximately the same at different inlet temperatures, inlet pressures and discharge pressures.
  • As each rotor passes the blower outlet the gas is compressed to the system pressure there and expelled.
  • Small but definite clearances allow operation without lubrication being required inside the air casing.
  • Timing gears control the relative position of the rotors to each other.

The rotary-lobe compressor was invented by two brothers, Philander Higley Roots and Frances Marion Roots, who patented their design in 1860.

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