Calculating Pump Horsepower
Calculating Pump Horsepower
(OP)
To calculate the Pump hp I have the following two equations,
Pump hp = (GPM x PSI)/(1714 x Efficiency) (1)
Brake hp (Shaft Power) = (GPM x Head, ft x SG)/(3960 gal/min/ft x Pump % Eff) (2)
With GPM = 22.44, and Head, ft = 38.4, and 60% Pump eff
Equation 1 yields, 1.94 hp
Equation 2 yields, 0.3627 hp
If Head, ft x 2.31 = PSI, and 1714 x 2.31 = 3960 (ignoring rounding off error), how come two different equations to calculate the same thing provide different answers? What am I missing here? Thanks.
Pump hp = (GPM x PSI)/(1714 x Efficiency) (1)
Brake hp (Shaft Power) = (GPM x Head, ft x SG)/(3960 gal/min/ft x Pump % Eff) (2)
With GPM = 22.44, and Head, ft = 38.4, and 60% Pump eff
Equation 1 yields, 1.94 hp
Equation 2 yields, 0.3627 hp
If Head, ft x 2.31 = PSI, and 1714 x 2.31 = 3960 (ignoring rounding off error), how come two different equations to calculate the same thing provide different answers? What am I missing here? Thanks.





RE: Calculating Pump Horsepower
RE: Calculating Pump Horsepower
RE: Calculating Pump Horsepower
Your answers are different by 2.31 x 2.
RE: Calculating Pump Horsepower
I suggest you lay the equations out with units and do a unit analysis to show you why ft * ft/psi gives you ft^2/lbf/in^2 or (ft^2*in^2)/lbf which is basically length to the fourth power over force.
Maybe you'd be ahead to look at ft / (ft/psi) or psi.
David Simpson, PE
MuleShoe Engineering
In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist
RE: Calculating Pump Horsepower