The heart of the centrifugal compressor is the impeller “stage”. The stage is made up of the following parts (illustrated in Figure 200-31):
• inlet guide vanes
• return bend (crossover)
• return channel
The stage can be separated into two major elements:
• The impellers which are mounted on the shaft as part of the rotor.
• The stationary components including the inlet nozzle and other components mentioned above.
The inlet volute, or return channel, guides the gas to the eye of the impeller, and aided by the guide vanes, distributes the flow around the circumference of the impeller eye.
One method of adjusting the stage performance, is to use different guide vane angles. This changes the angle of incidence on the impeller which in turn varies the head, efficiency, and stability. There are three types of fixed guide vanes; radial, against-rotation, and with-rotation. The influence of various guide vane angles on a given impeller head characteristic is shown in Figure 200-32.