Abstract: My invention relates to centrifugal compressors, more particularly to compressors of a known type, in which air enters the compressor rotor parallel to its axis of rotation, engages an inducer portion of the compressor rotor blades which is generally helical, in which the air is accelerated tangentially, and then proceeds through an impeller portion of the rotor formed with substantially radial vanes in which the air is further accelerated tangentially, leaving the rotor periphery with a high tangential velocity. In such a compressor, the air discharged from the rotor is received in a diffuser in which the velocity head of the air is largely converted to static head by a so-called diffusion process of reducing the air velocity. The air is then directed to the outlet or outlets of the compressor. It is to be understood, however, that this invention is concerned not with the rotor but rather with the vaned portion of the diffuser.