Page 171 - Centrifugal Pumps Design and Application

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 cav-
ity. Originally developed with double-suction impellers to reduce
NPSHR at high flow rates, this design is extremely flexible. Two appli-
cations 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 reduc-
ing pump speed. A more economic approach would be to install a bi-
rotor pump with case construction that permits operation of the impellers
either in series or in parallel. The conventional, integral cast cross-over