Page 68 - Centrifugal Pumps Design and Application

Volute Design 51

Figure 5-1. Volute velocity/impeller peripheral velocity ratio.

The hydraulic characteristics of a volute casing are a function of the
following design elements:

• Impeller diameter
• Cutwater diameter—This is directly related to specific speed as shown
in Table 3-2.
• Volute Up angle—This is selected to suit the absolute flow angle at the
impeller discharge. However, considerable deviation is acceptable in
Sow to medium specific speed pumps.
« Volute areas—These are so arranged that areas increase gradually from
the volute tongue or cutwater, toward the volute nozzle, thus accommo-
dating the discharge along the impeller periphery.
• Volute width (b 3)—This is made 1.6 to 2.0 times the impeller width (b 2)
(Table 3-1).
« Discharge nozzle diameter
« Throat area—This area is the most important factor in determining the
pump capacity at BEP and is determined using Figure 3-8.