Page 64 - Know and Understand Centrifugal Pumps

Useful Work and Pump Efficiency

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It is not practical to declare the flow without the accompanying head requirements. I
For this reason, when someone asks for the pump specifications, they need to know
the flow in gallons per minute and the head in feet.

The available areas in the impeller, and the available area in the
volute determine the flow, gpm. There are two critical areas in the
impeller, the exit area and the entrance area. For the volute casing,
the most important area is the ‘cutwater’. All fluid must pass this
point.
Head or pressure is developed in the pump; when the impeller
imparts rotational energy to the liquid (increasing the liquid’s
velocity), and then the volute converts this energy (by decreasing
the velocity) into pressure.
The relationship between the ‘exit area’ of the impeller, and the
‘cutwater area’ of the volute, generally determine the flow of the
pump.
See the illustration below (Figure 5-3):

ROTATION
Figure 5-3
~~~ ~ ~~
I &
F1
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