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Slurry Pump
WH14AAAAAA0EN_04D.DOC JAN 04-W08
Desccription of operation
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DESCRIPTION OF OPERATION
4.1 General
Centrifugal pumps work best with minimum wear and other mechanical stress if the
operating point is close to the pump's best efficiency point (BEP). To choose a pump that
works close to its best efficiency line (BEL), it is important to understand how the pump
interacts with the piping system in which it is installed.
In simple terms, a pump and its piping system act as two communicating vessels. The
piping sysem has a resistance curve that starts at the static delivery head, at zero flow. As
the flow increases, the resistance increases with pipe friction. A radial centrifugal pump
has a descending discharge/flow curve for each rpm. The pump's operating point (DP) at a
given pump speed is the point of intersection between the piping system's resistance
curve and the pump's discharge/flow curve. See diagram below.
It is therefore important to calculate the piping
system's resistance curve correctly and to take into
account the manner in which the admixture of solid
particles, for example, affects the curves of the piping
system and pump. We recommend using
Pumpdim™ for Windows™ for our pump
applications.
To obtain the best wear properties the pump can be
provided with different materials in the parts exposed
to the greatest wear.
4.2 Best efficiency point
Pressure conditions in the pump casing are shown in Figure 4.2-1. At the BEP there is
even pressure round the impeller, resulting in small radial forces which in their turn exert
little load on bearings and cause little shaft deflection. When the pump operates at low
capacity and not at BEP, differential pressure builds up over the casing volute. This gives
rise to a radial force F on the impeller which is a function of the differential pressure (Pa)
and the impeller's projected area (mm
2
).
Q
H
DP