Publisher Summary This chapter presents the uses of variable-speed (V/S) pump operation in water and wastewater pumping stations. A station with V/S pumps must be able to accommodate any flow (from minimum to maximum) and operate in a normal manner when any one of the pumps or drives is out of service. A V/S pumping station that includes constant-speed (C/S) pumps could provide the same results as a station with all V/S pumps, but only if the relationship between the sizes of the two kinds of pumps is correct. For V/S pumping, the wet well need only be a sump for pumping at the instantaneous system flow rate. The only storage required is enough to allow pumps to be shut down or started up without an excessive change in water level, and the water surface area needed for that purpose is quite small. When the pump discharges into a hydraulic system, the power delivered by the pump at any point on the system head curve is determined by the flow rate and the head at that point. The purpose of a V/S booster pump is to maintain a nearly constant discharge pressure while delivering the variable flow rate needed in a closed distribution network. Pump speed variation controls the pump discharge pressure, and the flow rate is determined by the system demand. Both the V/S pump characteristic curves and the curve of required pump differential head versus flow rate must be considered in order to analyze the operation of a pump that discharges into a hydraulic network.