Centrifugal Pumps Design and Application 2nd ed - Val S. Lobanoff, Robert R. Ross (Butterworth-Heinemann, 1992)

148 Centrifugal Pumps: Design and Application
Figure 10-10. Volute inserts.
Bi-rotors
Unusual pipeline requirements can often be satisfied using bi-rotor
pumps. These are basically two single-stage pumps on the same shaft,
with two conventional incoming and outgoing nozzles at each body cavity.
Originally developed with double-suction impellers to reduce
NPSHR at high flow rates, this design is extremely flexible. Two applications
are now described.
Bi-rotor pipeline pump. The pipeline conditions illustrated in Figure
10-15 have an ultimate pipeline capacity of 60,000 GPM requiring three
pumps operating in parallel with each pump delivering 20,OCX) GPM at
maximum pipeline pressure. During the early life of the pipeline, initial
throughput would be 40,000 GPM. This would normally mean operating
two pumps in parallel and throttling out excess pump pressure or reducing
pump speed. A more economic approach would be to install a birotor
pump with case construction that permits operation of the impellers
either in series or in parallel. The conventional, integral cast cross-over