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Publisher Summary This chapter provides an introduction to centrifugal pump theory that is required to consider when selecting and specifying centrifugal pumps in water and wastewater pumping applications. The centrifugal pumps are divided into three groups that include radial-flow pumps, mixed-flow pumps, and axial-flow or propeller pumps. The operating characteristics of pumps depend on their size, speed, and design. Pumps of similar size and design are produced by many manufacturers, but they vary somewhat because of slight design modifications. The basic relationships that could be used to characterize and analyze pump performance under varying conditions include energy transfer in pumps, flow, head, and power coefficients, affinity laws, and specific speed. Cavitation is the formation and collapse of vapor cavities within the pump. When cavitation occurs in pumps, it has the potential to cause performance degradation, namely, loss of head, capacity, and efficiency and permanent damage due to erosion and mechanical failure of pump components and structures. In most pump curves, the total dynamic head H in m (ft), the efficiency E in percent, and the power input P in kW (hp) are plotted as ordinates against the flow rate Q in m 3 /s or m 3 /h (gal/min or Mgal/d) as the abscissa. Nondimensional pump curves are obtained by expressing head, flow rate, power input, and efficiency as percentages of the corresponding values at the best efficiency point, and such curves are useful for comparing the hydraulic properties of pumps belonging to the same type and assessing the performance of pumps of different specific speeds for various applications. |
