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The Practical Pumping Handbook ~- ...............................................................................................................................................

This arrangement is not frequently
used for pumps designed to
handle solids, where the second
volute would cause considerable
clogging problems. However,
there are a few exceptions, and
their success tends to depend on
the nature of the slurry and the
specific design of the casing.

2.5.1 Radial thrust
The magnitude of the radial thrust
at Shut-off condition (zero flow)
will depend on the design of the Figure 2.13. Radial forces in double volute
impeller and the shut-off head. A casing
radial thrust factor (Kso) can be
established and tends to vary
between 0.15 and 0.38 depending on the design of the impeller and its
specific speed. This factor is then used in the equation shown below to
calculate the approximate radial force (Fso) that can be expected at the
shut-off condition.

Fso = Kso x Pso x D x B

where Kso = Radial Thrust Factor
Pso = Differential Pressure at Shut-off

D = Impeller Diameter
B = Impeller Width at perimeter (incl. shrouds)
In a fairly typical process pump where the impeller is 13 inches in
diameter and the operating speed is 3600 rpm, the radial force can be as
high as 800 pounds at the shut-off condition. Radial force values at
other operating conditions can be approximated by the following
equation when the test data exponent (x) is available.
i- "]
t i -aj

where Fso = Radial Force at Shut-off
= Exponent based on pump test data
= Capacity at Operating Condition (USGPM)
Qn = Capacity at BEP in USGPM

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