Problem 3 (Hazen Williams Nomograph and Pump HP-25 Points): A pump station, loca

Question

Problem 3 (Hazen Williams Nomograph and Pump HP-25 Points): A pump station, located at Point D, pumps water from Tank A to Tank B. The pumps operate in parallel, and both pumps are operating. Given a flow of 1800 gpm, Tank A to Tank B, determine the horse power of each pump, if the efficiency of each pump at this operating point is 60%, and determine the absolute pressure in the intake to each pump. Ambient air pressure is 14 psi. Use the attached Hazen Williams Nomograph; do not use Hazen Williams Equation

Explanation / Answer

1. Assuming that the combined discharge efficiency = 0.6

Hence, design discharge for each individual pump = 1800/0.6 * (1/2) = 1500 Gpm

From point A to D,

Head loss in ft. from Hazen williams Nomogram for Design discharge of 1500 GPm = 11.44 ft

Head loss in ft = 0.002083 * (100/C)^ 1.85 * (gpm^1.85)/(d^4.8655) = 11.44 ft.

Net head available at the point D = 150 - 11.44 = 138.56 ft.

and Head lost in delivering to tank B = 11.44 ft as the Discharge and Length if pipe from point D to tank B are same.

Gross Head for working of the each individual pump = 200 + (11.44) + (11.44) = 222.88 ft.

Thus, power required for each pump,

P = density of water * acceleration due to gravity * Discharge * (Head + Head Loss) = Q*H*(Specific gravity) /( 3960)

Q = Discharge in Gpm , H = Head to be lifted + Head Loss in ft

and Power is in HP

thus P = 84. 24 HP

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