67
Pressure Tank Precharge - The pressure
of compressed air stored in a captive air
pressure tank. A reading should be taken
with an air pressure gauge (tire gauge) with
water pressure at zero. The air pressure is
then adjusted to about 3 PSI lower than the
cut-in pressure (see Pressure Switch). If
precharge is not set properly, the tank will not
work to full capacity, and the pump will cycle
on and off more frequently.
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Glossary of Solar Electricity and Water
Pumping, please contact Dankoff Solar
Products. Citation of the source and copyright
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Copyright © 1997-2005 by Dankoff Solar
Products, Inc.
All rights reserved
13.10 Calculating Pumping
Efficiency and Power
Requirement
Glossary of Solar Electricity and Water
Pumping continued
This formula lets you calculate the wire-to-
water energy efficiency of any electric pump-
ing system
% Efficiency = (Vert. Feet X GPM X 18.8) /
Watts
Metric: % Efficiency = ( Vert. meters X
LPM X 16 ) / Watts
% is expressed as a whole number (“45”
means 45%)
To estimate power requirement for any
proposed pumping job
Watts = ( Vert. feet X GPM X 18.8 ) /
pump efficiency %
Metric: Watts = (Vert. meters X LPM X 16)
/ % pump efficiency
Average efficiency for AC electric pump is
around 35%, solar pumps range 40-60%.
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