Chapter 12 - Pumps: Intake Design, Selection, and Installation

Abstract

This chapter deals with wet well design, pump piping, and selection of pumping equipment. The pump intake design must satisfy several requirements for proper approach conditions by avoiding poor velocity distribution at the entrance to the pump, excessive swirling in the pump intake piping, air entrainment in the pumped flow, unstable approach conditions in multiple pump operation, and vortices. Model studies are useful for finding and correcting faults in the hydraulic flow patterns in wet wells. The ANSI/HI 9.8-1998 standard requires a physical model study if the sump or piping geometry differs from the standard, the approach flow is non-uniform or unsymmetrical, and the flow rate is more than 2520 L/s (40,000 gal/min) per pump or the total flow exceeds 6310 L/s (100,000 gal/min) with all pumps running. Several factors that need to be considered during pipe selection include quality of the fluid to be pumped, required design capacity (initial minimum, average, and maximum flow rates), operating conditions (best-case and worst-case system head curves, maximum and minimum flow rates, submergence, and/or NPSH). A step-by-step procedure for selecting pumps involves developing the calculations for the performance requirements completely and on the basis of the best- and worst-case assumptions for system dynamic headlosses, specifying materials that are suitable for the application, specifying the proper balance grade number, and deciding the number of pumps to be used and the type of pump.