The inlet nozzle accelerates the gas and directs it to the inlet guide vanes. Inlet guide vanes may be fixed or adjustable.  On a multi-stage compressor, the inlet nozzle is generally radial. The inlet guide vanes are necessary to properly distribute the flow evenly to the first stage impeller. Single-stage compressors may or may not require inlet vanes.
	Gas enters the center of the impeller, called the suction eye, and centrifugal force accelerates it out to the impeller’s perimeter into the diffuser. Interstage seals are required at the impeller eye and rotor shaft to prevent gas backflow from the discharge to inlet.
	The diffuser reduces the velocity and converts the kinetic energy to a pressure increase.
	The return channel directs the flow of gas from the diffuser and introduces it to the next impeller.
	For the last stage of compression, the flow leaving the diffuser enters the discharge volute and exits through the discharge nozzle.
	The volute is a continually widening passage that slows the gas and increases its pressure to a maximum.