Page 152 - Centrifugal Pumps Design and Application

130 Centrifugal Pumps: Design and Application

Figure 9-13. Bowl assembly with double suction first stage.

Small Boiler Feed Pumps

In design, these pumps are quite similar to heater drain pumps, al-
though the NPSH margin is usually sufficient not to require injection to
the suction case bearing. The mechanical seal should be located in a
stuffing box, mounted externally on the discharge head. The minimum
recommended material selection is cast iron bowls, martensitic steel im-
pellers, and carbon/graphite bearings.

Cryogenic Pumps

Vertical barrel pumps are particularly well suited for cryogenic applica-
tions. Being vertically suspended, thermal contraction and expansion will
not cause pump misalignment as long as reasonable precaution is taken in
dealing with nozzle forces at the suction and discharge flanges. Because the
motor is supported on top of the discharge head, it is automatically aligned
to the pump. The external pump configuration is simple and easy to ther-