The Roots blower has internal rotors that turn against each other. The type of blower that we use has three lobes per rotor, with as advantage that the three-lobe produces less noise. These lobes roll over each other and do not touch the pump housing. The pump housing is oil-free.
As the rotors turn, air in the inlet is trapped between the rotor lobes and the casing and is carried round to the outlet without being compressed.
The casing bore toward the discharge port is slightly eccentric so that as the lobe approaches the port the gap between it and the casing begins to widen. This allows gradual equalisation of pressure between the air in the discharge port and that in the chamber behind the advancing lobe. Pressure equalisation in two-lobe blocks occurs abruptly as the advancing lobe crosses the lip of the discharge port. This is the main reason why three-lobe blocks generate significantly less pulsation than two-lobe blocks. The air is then finally pushed out against the pressure in the pipework.
If vacuum (yellow) occurs between the rotor and the casing ambient air (blue) enters the blower block via so-called pre-inlet channels as the rotors continue to turn. The two volume flows subsequently combine and the arising compression heat is dissipated throughout a much larger volume of trapped air. This approach therefore achieves the same discharge temperatures that are produced by normal blower blocks.