Question

A centrifugal pump is used to pump water at 77ºF from a reservoir whose surface is 20 ft above the centerline of the pump inlet. The Pipe System consists of 67.5 ft of PVC pipe with a 1.2 in ID and negligible average internal roughness height. The length of the pipe from the bottom of the lower tank to the pump inlet is 12 ft. There are several minor losses in the pipe: an acute edge entry (KL = 0.5), two normal smooth flanged 90 ° elbows (KL = 0.3 each), two fully open flanged globe valves (KL = 6.0 each) and a loss of output to the upper reservoir (KL = 1.05). The manufacturer provides the positive net suction load required from the pump as a curve fitting: NPSHrequired = 1 ft + (0.0054 ft / gpm2) Q2, where Q = flow is in gpm. Estimate the maximum flow (in units of gpm) that can be pumped without cavitation.

It also specifies an appropriate pump for this system, which would deliver the desired flow. For the selected pump, determine:

a) The input power to the pump

b) The required NPSH and the available NPSH

c) Efficiency at the point of operation

d) Diameter of the impeller

Answer 1

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