Page 128 - HVAC Pump Handbook

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Physical Description of HVAC Pumps

Physical Description of HVAC Pumps 125

Any application that has a possibility of dirt or other foreign matter
may be an application for packing. Typical of these are condenser
pumps taking water from cooling tower sumps. Also, large facilities
with full-time maintenance personnel who are experienced in the
technique of installing packing in all types of rotating elements may
be candidates for packed pumps. Properly installed packing can elimi-
nate waste water caused by continuous dripping.
Why use packing? A mechanical seal, when it fails, may throw water
around the equipment room, while packing, as it starts to fail, just
leaks water from the gland. Its failure is much more gradual than that
of mechanical seals. The other reason may be because the client’s per-
sonnel prefer packing; therefore, this is one question that the designer
should ask when considering the pumps on a particular installation.

5.7 Internal Forces and Leakages in
Centrifugal Pumps

The centrifugal pump, regardless of type, is subjected to dynamic forces
and leakages, which must be controlled to ensure that a successful
design is achieved for each particular application. It is important that
the water system designer understand these basic conditions of cen-
trifugal pump operation. Figure 5.15 describes these forces and leakages
for a volute-type pump, while Fig. 5.16 provides the same for an axial-
flow-type pump, which has a common name of “vertical turbine.”

Figure 5.15 Forces and leakages in a volute-type pupm.

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