Must multiple pumps operated in series or parallel be identical in size?
A. No, they do not have to be identical. However, pumps intended to operate in series must be close in size regarding flow rate-for example, lower speed booster pumps used to provide an increase in NPSHA for high-pressure pumps. Pumps for parallel operation must be close in total head developed; otherwise, one or more pumps may be forced to operate at shut off or at unacceptably low flows. A thorough review of the entire operating curve for each pump must be made. Pumps operating in series produce head that is additive at the flow rate at which they would run individually. Two pumps, each capable of 1,000 m3/h (4,400 gpm) at 50 m (165 ft) of head, when connected in series could deliver 1,000 cubic meters per hour (4,400 gpm) at 100 m (330 ft) of head. Series operation is therefore used where higher pressures are required than the pressures that an individual pump can supply. Pumps used in series must be capable of the increased pressure levels that result from staging. See Figure 1.3.6
