Centrifugal Pumps Design and Application 2nd ed - Val S. Lobanoff, Robert R. Ross (Butterworth-Heinemann, 1992)

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 relatively
low. Above 700-1,000 GPM, efficiency is high and required
NPSH is low. All modern double-suction pumps are designed with double-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 entrained
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.
Pump Casing
Double-Suction Pump Design
The double-suction, double-volute casing is designed in identical manner
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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