Page 236 - Centrifugal Pumps Design and Application

210 Centrifugal Pumps: Design and Application

Waterflood Pumps

Oil field water injection pumps operate at capacities to 5,000 gpm.
Double-case pumps provide differential heads to 11,000 feet and dis-
charge pressures to 8,000 psi from two pumps operating in series. This
application is covered in more detail in Chapter 10.

Pipeline Pumps

The vast majority of pipeline pumps are of the horizontally split, multi-
stage design, covered in Chapter 10. Double-case pumps are used only
when unusually high pressures are required or when handling hydrocar-
bons near their supercritical condition.

Design Features

Removable Inner Case Subassembly

Modern double-case pumps have a fully separate inner case subas-
sembly (including rotor). The inner case subassembly for a volute-type
pump is shown in Figure 12-4. This subassembly can be removed, after
disassembling the outboard cover, without disturbing the suction piping,
discharge piping or the driver. It is common practice to have a spare sub-
assembly available for replacement, thereby reducing maintenance turn-
around time or the downtime caused by unscheduled outages.
If the pumped fluid is hot, time is needed to lower the temperature of
the components before maintenance work can begin. Time to cool by am-
bient air is extended because the pump is normally well insulated. Forced
liquid cooling can be helpful, but must be preplanned to avoid subjecting
the pump to unacceptable thermal gradients.
In some designs the inner case subassembly includes the radial and
thrust bearings. This feature further reduces downtime because the re-
placement rotor is aligned before the outage. A boiler feedwater pump of
this construction, called "cartridge," "full cartridge," "pullout," or
"cartridge pullout" design, is shown in Figure 12-5.
A saltwater injection pump with full cartridge pullout is shown in Fig-
ure 12-6. The configuration shown is said to save at least 40 manhours of
labor, compared to conventional construction, each time the inner-case
subassembly is replaced. This design features a springplate on the high
pressure end to preload the internal gasket between the inner volute case
and the outer barrel. This gasket seals the full differential pressure. The
springplate design compensates for manufacturing tolerances to assure
interchangeability among spare inner assemblies and also compensates