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1-10 - Lecture 11 Pumps System Curves I Pump Efficiency and...

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Lecture 11 Pumps & System Curves I. Pum p Efficiency and Power Pump efficiency, E pump pump water horsepower WHP E brake horsepower BHP = = (221) n by the pump manufacturer calculate required BHP, knowing E pump Water horsepower is defined as: where brake horsepower refers to the input power needed at the pump shaft (not necessarily in “horsepower”; could be watts or some other unit) Pump efficiency is usually give Typically use the above equation to QH WHP 3956 = (222) where WHP is in horsepower; Q in gpm; and H in feet of head. The denominator is derived from: ( ) ( )( ) ( ) ( ) 3 3 62.4 lbs/ft gal/min ft QH QH 3956 33,000 ft-lbs/min-HP 7.481 gal/ft γ = (223) where γ = ρ g, and ρ is water density. In metric units: ( )( ) ( )( ) ( ) ( ) 3 2 3 1000 kg/m 9.81 m/s l/s m QH WHP gQH 102 1000 l/m 1000 W/kW = ρ = = (224) where WHP is in kW; Q in lps; and H in meters of head (225) Total Dynamic Head , TDH, is defined as: 1 HP=0.746 kW 2 f P V TDH Elev h 2g = ∆ + + + γ (226) Sprinkle & Trickle Irrigation Lectures Page 123 Merkley & Allen
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