5 - Useful work and pump efficiency

Abstract

This chapter explains useful work of a pump and pump efficiency along with James Watt's development of terms of energy, work, and power. He defined that energy is the capacity to perform work; work is a force multiplied over a distance; power is work performed within a certain specified time frame. This chapter also discusses how James Watt assigned 550 foot-lbs/sec to be one horsepower, which to date has been the standard definition of a horsepower (1 HP = 550 foot lbs/sec). The useful work of a pump is called water horsepower (WHp) and it is mathematically demonstrated as WHp = (H x Q x sp. gr.)/3960. Further, the chapter describes that the flow is the number of gallons per minute that the pump will discharge. This chapter also explains the pump efficiency and methods used for calculating pump efficiency. Pump efficiency is affected by numerous factors and impeller is the main factor among those. The factors affecting pump efficiency is listed as surface finish of internal surfaces, wear ring tolerance, mechanical losses, impeller diameter, viscosity, size of solid particles, and the type of pump.