Page 94 - HVAC Pump Handbook

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Source: HVAC Pump Handbook

Chapter
4

Basics of Pump Design

4.1 Introduction
A pump is a wheel rotating on stick. Some wheel; some stick! So much
has been written on pumps, but often this material had to be in tech-
nical terms that made it difficult for the HVAC designer to under-
stand how a pump functions. It is the intent of this Handbook to pre-
sent pumps so that it is easy for the HVAC water system designer or
operator to understand their operation. This can be done because
most HVAC systems use water, not hydrocarbons or other liquids
with broad ranges of viscosity and specific gravity. Several chapters
are devoted to pumps to clarify (1) the basics of pump design, (2) the
pump’s physical arrangement, (3) pump performance, (4) motors and
drives for pumps, and finally, (5) applying pumps to HVAC systems.
The centrifugal pump creates pressure on a water stream that can be
used to move that water through a system of piping and equipment. The
amount of pressure that the pump can create depends on the flow
through it. Its fundamental performance curve is called a head-capacity
curve and is described in Fig. 4.1a. The flow measured in gallons per
minute, is plotted horizontally, while the head measured in feet, is
plotted vertically. Pump head is always shown in feet of liquid rather
than pounds of pressure. With head measured in feet, the pump curve
is applicable to any liquid of any specific gravity. Only when calculating
the brake horsepower of the pump does specific gravity become involved.
The feet of head per pound of pressure for any liquid is

Feet of head H 144
(4.1)
Pounds of pressure

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