Chapter hvac engineering Fundamentals: Part 1 Introduction

Design Procedures: Part 4
183
Figure
6.30
Vertical
in-line
pump. (
Courtesy of ITT-Bell and
Gossett.
)
Figure 6.31
Pump performance curve.
Design Procedures: Part 4
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184
Chapter Six
Figure 6.32
Pump speed versus capacity and head.
peller diameters. The same impeller is used throughout, but when it
is ‘‘shaved’’ (machined) to reduce the outside diameter, the capacity is
reduced. This allows the pump to be matched to the design conditions.
The graph includes brake horsepower curves for standard-size motors,
based on water with a specific gravity of 1.0. For brines, or liquids
with other specific gravities, the horsepower must be corrected in di-
rect proportion to the specific-gravity change. Also shown are effi-
ciency curves.
The point at which a pump curve intersects the no-flow line is the
shutoff head.
At this or a higher head, the pump will not generate any
flow. If the pump continues to run under no-flow conditions, the work
energy input will heat the water. The resulting temperature and pres-
sure rise has been known to break the pump casing.
If the speed of the pump is varied, the result will be a family of
curves similar to Fig. 6.32. These data are needed to evaluate a vari-
able-speed pumping design.