Page 47 - Centrifugal Pumps 2E

Impeller Design 33

Step 8: Estimate NPSHR.

From Figure 3-6:

Step 9: Determine volute parameters,

To finalize the impeller design, we must consider any mechanical
limitations of the pump casing. Designing the impeller alone is not suf-
ficient as we must see how it physically relates to the volute area,
cutwater diameter, volute width, etc,

• Volute area. Figure 3-7 shows a number of curves for volute velocity
constant K 3. These represent the statistical gathering efforts of a
number of major pump companies. Figure 3-8 shows the average of
these curves and is recommended for estimating volute area.

The calculated volute area is the final area for a single volute pump.
For double-volute pumps, this area should be divided by 2, and for
diffuser type pumps it should be divided by the number of vanes in
the diffuser casing.