Pump Series Units
For large-capacity medium-high-head conditions, two single-stage, double suction pumps can be connected in a series on one baseplate with a single driver. Such an arrangement was at one time very common in waterworks applications for heads of 250 to 400 ft (76 to 122 m). One series arrangement uses a double-extended shaft motor in the middle, driving two pumps connected in a series by external piping. In a second type, a standard motor is used with one pump having a double-extended shaft. This latter arrangement may have limited applications because the shaft of the pump next to the motor must be strong enough to transmit the total pumping horsepower. If the total pressure generated by such a series unit is relatively high, the casing of the second pump could require ribbing. Higher heads per stage are becoming more and more common, and series units are generally used in only very high ranges of total head.