Page 95 - Centrifugal Pumps Design and Application

7

Double-Suction

Pumps and

Side-Suction

Design

The double-suction single-stage pump is, perhaps, the most widely
used pump throughout the industrial world. Applications range from
light duty building trade pumps to heavy duty pipeline injection pumps
(Figure 7-1).
The double-suction is a very simple machine whose initial cost is rela-
tively low. Above 700-1,000 GPM, efficiency is high and required
NPSH is low. All modern double-suction pumps are designed with dou-
ble-volute casing to maintain hydraulic radial balance over the full range
of the head-capacity curve. Having a double-suction impeller, the pumps
are theoretically in axial balance. Double-suction pumps often have to
operate under suction lift, run wide open in a system without a discharge
valve, or satisfy a variable capacity requirement. These pumps may be
quite large, pump high capacities, and handle pumpage with gas or en-
trained air. In spite of all this, they are expected to operate without noise
or cavitation. Suction passage design should therefore be based on the
best available technical "know-how," and liberties should not be taken
during the design process.

Double-Suction Pump Design

Pump Casing

The double-suction, double-volute casing is designed in identical man-
ner to the single-suction pump, as described in Chapter 5. The specific
speed, N s, of a double-suction pump is identical to the single-suction
unit. Do not divide calculated pump specific speed by the square root of

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