Patent ID: 8414249

Claim:
A compressor comprising: a housing defining a gas inlet and a gas outlet; a radial impeller wheel having a plurality of vanes and mounted in the housing between said inlet and outlet, the wheel being rotatable about an axis; the inlet comprising a substantially tubular outer wall extending away from the impeller wheel in an upstream direction and forming a gas intake, and a substantially tubular inner wall extending away from the impeller wheel in an upstream direction and within the outer wall, the inner wall defining an inner surface at least a portion of which is located in close proximity to radially outer edges of the vanes of the radial impeller which sweep across said surface as the radial impeller wheel rotates about its axis; a substantially tubular gas flow passage defined between the inner and outer walls and extending from an upstream end to a downstream end proximate to the radial impeller wheel; an upstream opening defined by the flow passage providing communication between said passage and said intake; at least one first aperture downstream of the upstream opening and providing communication between the passage and the inner surface of the inner wall; an axial impeller wheel having a plurality of vanes and supported for rotation in said inlet upstream of the radial impeller wheel; and a stator comprising a plurality of fixed vanes and disposed in the inner wall of the inlet between the radial and axial impeller wheels, wherein the at least one first aperture is located over the vanes of the radial impeller, and wherein there is provided at least one second aperture and at least one third aperture in said inner wall at locations axially spaced from the at least one first aperture, said second aperture being disposed over the vanes of the stator and the third aperture being disposed over the vanes of the axial impeller.