Page 98 - HVAC Pump Handbook

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Basics of Pump Design

Basics of Pump Design 95

Figure 4.3 Inlet and discharge vector diagrams. (From Karassik et al., Pump
Handbook, 3d ed., McGraw-Hill, used with permission.)

Inspection of an HVAC centrifugal pump impeller will reveal slots on
the periphery of the impeller. These slots are narrow for low-capacity
pumps and wide for higher-capacity pumps. The angle of the vane as
it reaches the periphery of the impeller reveals the angle that the
pump designer has selected for the vector W (Fig. 4.2a).
2
Pumps are highly specialized devices designed for very particular
applications in order to achieve maximum efficiency and ease of use.
HVAC pumps come under the broadest classification of centrifugal
pumps—those for clear water service. Since corrosion and erosion are
not factors in this pump service, the designer can concentrate on first
cost, efficiency, and ease of operation and maintenance, the three dri-
ving forces in any product design. Much work is done by the pump
designer in developing the internal passages of the impeller to
achieve maximum, economical smoothness that will provide a mini-
mum of friction to the water passing through the pump. Here lies a
simple evaluation that can be made by any buyer of pumps. How
smooth and how well are the internal passages of a pump impeller
developed? How uniform are the internal vanes and leaving ports of
the impeller? How uniform and smooth are the vanes at the suction

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