The efficiency of the Impeller Pump can be
greatly increased by the addition of stationary Diffuser Vanes. Large Impeller-diffuser
pumps can achieve efficiency ratings of 90 percent.
The number of diffuser
vanes is always different than the number of impeller vanes. This is so that the
edges of the rotating impeller vanes do not come close to all the ends of the
diffuser vanes at the same time.
This prevents thumping or knocking, and excessive
buildup of pressures.
In this drawing the innermost set of vanes revolves
and the outer set is stationary.