Diffuser:
A few centrifugal pumps hold diffusers. A diffuser is a set of stationary vanes which surround the impeller. The reasons of the diffuser are to raise the effectiveness of the centrifugal pump through permitting a more gradual expansion and less turbulent area for the liquid to decrease in velocity.
The diffuser vanes are designed in a manner in which the liquid exiting the impeller will encounter an ever rising flow area as it passes by the diffuser. That increase in flow area causes a reduction in flow velocity and converting kinetic energy within flow pressure.
Figure: Centrifugal Pump Diffuser