13-11-2012, 06:20 PM
Performance of Centrifugal Pumps
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. Classification of Centrifugal Pumps
In colloquial usage in the United States, a "centrifugal
pump" is any pump in which the fluid is energized by
a rotating impeller, whether the flow is radial, axial, or
a combination of both (mixed). Strictly defined (as in
European practice), a centrifugal pump is a radial-flow
pump only. But colloquial usage is followed here, and
thus centrifugal pumps are divided into three groups:
• Radial-flow pumps
• Mixed-flow pumps
• Axial-flow or propeller pumps.
Pump Application Terminology, Equations, and Performance Curves
The basic terminology, equations, and curves for
defining pump performance and solving pump problems
are given in this section. The development of the
pump performance curves, which are used to define
the operating characteristics of a given pump, is
reviewed briefly at the end of this section (this subject
is covered in more detail in Chapter 12).
Input Power
Pump performance is measured in terms of the flowrate
that a pump can discharge against a given head at
a given efficiency. The pump capacity depends on the
design, and design information is furnished by the
pump manufacturer in a series of curves for a given
pump. Pump efficiency, Ep, is the ratio of the useful
power output (water kilowatts [wkW] or water horsepower
[whp]) to the power input to the pump shaft.
Hence, the brake power (bkW) that must be supplied
by the drive is, in SI units,