How can you estimate the efficiency of a pump?

How can you estimate the efficiency of a pump?
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Answer :

The following method, developed by M.W. Kellogg, gives results within 3.5% of most manufacturers’  curves. Eff % = 80-0.2855H+3.78×10-4HF-2.23×10-7HF2+5.39×10-4H2-6.39×10-7H2F+4.0×10-10H2F2 H =  Developed head, ft F = Flow in GPM (gallons per minute) Applicable for heads from 50 to 300 ft and  flows from 100 to 1000 GPM
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