Page 234 - Centrifugal Pumps Design and Application

208 Centrifugal Pumps: Design and Application

Diffuser Casings with Balance Drum

Diffuser-type pumps have all impellers facing in one direction, result-
ing in high axial thrust forces. Figure 12-2 shows a diftuser-type pump
with a balance drum to carry the axial thrust forces. The inner case as-
sembly is vertically split, and the symmetry of the diffusers provides ra-
dial hydraulic balance.

Diffuser Casings with Balance Disk

Figure 12-3 shows the diffiiser-type configuration with a balance disk
that carries the axial forces. Except for the axial balancing device, the
construction is similar to the previous diffuser-type design. Balance disk
construction is used for clean services such as boiler feed because of its
ability to completely balance axial thrust at all operating flow rates.

Figure 12-2. Diffuser-type in-line impeller, double-case pump with balance drum
(courtesy Dresser Pump Division, Dresser Industries, Inc.).

Applications

Common applications for double-case pumps are:

« Boiler feed pumps in central station and large industrial fossil-fueled
power plants.
• High pressure and/or high temperature pumps in oil refineries or
chemical plants.