Patent ID: 8287236

Claim:
A multistage centrifugal compressor comprising: a rotary shaft; a centrifugal impeller formed of a hub, a shroud, and blades in a radial cascade arrangement between the huh and shroud and attached to the rotary shaft in a plurality of stages; an annular suction passage disposed upstream of the centrifugal impeller to guide a fluid flow from an inward radial direction to a blade inlet; a diffuser disposed downstream of the centrifugal impeller; and a return channel formed of a bend. portion disposed downstream of the diffuser and a guide blade portion disposed downstream of the bend portion, wherein an axial parallel portion is disposed in the annular suction passage at a side of the hub, and a passage cross-section area of the annular suction passage at a position where a radius at a shroud side becomes a minimum is 70%-95% of a passage cross-section area of the blade inlet.