 The
simplest type of centrifugal pump is the single stage machine that consists
fundamentally of a rotating element, called an impeller, and a casing.
Liquid is led to the eye or center of the impeller and is set into rotation
by the impeller vanes. By virtue of centrifugal force the liquid is thrown
from the rim or periphery of the impeller with a considerable velocity
and pressure. The casing, which closely surrounds the impeller, has a
volute shaped passage of increasing area, which collects the liquid leaving
the impeller, and converts a portion of its velocity energy into additional
pressure energy. This casing passage leads to the discharge nozzle of
the pump where it is forced into the discharge piping.
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