– The impeller is the main component of a centrifugal pump. Consists of a series of curved vanes.  There is normally sandwiched between two discs.  For the fluids with entrained solids, there is an open or semi-open impeller (backed by a single disc) is preferred (look at Figure 1).

The fluids enters the impeller at its axis on the shaft and exits along the circumference between the vanes.  The impeller, is on the opposite side to side, there is connected through a drive shaft to a motor and rotated on high speed (between 500-5000rpm).  Rotational of the impeller accelerates the fluids out through the impeller vanes into the pump casing. There is two type basic design of casing: volute and diffuser,  purpose in both designs is to flow the fluid into a controlled discharge at the pressure.

At the volute casing at the offset of impeller, effectively creating a curved funnel with an increasing, make it cross-sectional area towards the pump outlet.  This design causes of fluid pressure increase towards the outlet (look at Fig 2).
centrifugal pump
Basicly applies to diffuser designs.  In this case, pressure of the fluid is increases as fluid is expelled between a set of stationary vanes surrounding the impeller (Fig 3).  Designs can be tailored for the specific applications and can to be more efficient.  Cases of the volute are better suited to applications involving entrained solids or high viscosity fluids when it advantageous to avoid the constrictions of diffuser vanes.  The Design of asymmetry of the volute can result in greater wear on the impeller and drive shaft.
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