Page 136 - HVAC Pump Handbook

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Physical Description of HVAC Pumps

Physical Description of HVAC Pumps 133

Figure 5.21 Discharge valves
for variable-speed pumps.

partially without any indication of this condition. This creates a terri-
ble waste of pumping energy. Also, some multipurpose valves must
have another valve downstream of them to repair the check-valve fea-
ture of the multipurpose valve. A separate check valve and shutoff
valve should be provided instead. They are lower in cost and usually
have a lower friction loss than comparable multiple-duty valves.
On continuously running pumps taking suction from a tank below
the pumps, the greater efficiency of the standard centrifugal pump
should give it priority over a self-priming pump. It will be necessary
to provide a priming means to get the pump started. This can be a
priming tank or a separate source of water. This tank holds enough
water to keep the pump flooded until it has primed the suction line.
With a properly sized priming system, the standard centrifugal pump
evacuates the air in the suction line and continues to pump water
from the lower tank. There are manufacturers of priming systems for
centrifugal pumps, and there is considerable information in the pump
references on the actual design of a priming system. The NPSHR
characteristics of the pump must be checked carefully when taking
suction from lower tanks.

5.9 Bibliography

Additional centrifugal pump descriptions and performance can be found
in the catalogs of (1) the AC Pump Division of the ITT Fluid Technology;

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