Page 63 - Centrifugal Pumps Design and Application

46 Centrifugal Pumps: Design and Application

Mechanical variables include:

» Open or closed or semi-open impellers,
• Single-stage or multi-stage.
• Vertical or horizontal.
» With water jacket or without.
« Overhung or two-bearings design.
• Close-coupled or coupled units.
« Stiff shaft or flexible shaft design.
• Single volute, double volute, quad volute.
• Short elbow-type or turbine-type diffusers.
• Mechanical seals or packing.
« Stuffing boxes with bleed-offs or with clean flush injection.
• Ball, sleeve, or Kingsbury-type bearings.
• Oil rings, forced feed, oil mist, submerged or grease packed lubrica-
tion,,

It can be seen from the variables listed that it is a complex job for a
pump designer to design the right pump for the right environment.
After complete hydraulic and mechanical specifications are estab-
lished, the designer should be ready for pump layout documents.
General pump design can be classified in the following categories:

1, Design a new pump to satisfy basic engineering requirements such
as shape of H-Q curve, NPSHA, efficiency, etc.
2, Design a new pump to satisfy special applications such as boiler-
feed, nuclear coolant, pipeline, large circulator, condensate, sec-
ondary recovery, etc.
3, Design a new line of pumps, such as API pumps, ANSI pumps,
double-suction pumps, pulp and paper pumps, building trade
pumps, boilerfeed pumps, etc.

Performance Chart

For pumps in any category, an overall performance chart should be
prepared (if not available) as a first step in the design study. This chart
will establish the flow and head for each pump, establish the number and
size of pumps required to satisfy the range chart, and avoid overlap or
gaps between pump sizes. Even if only one pump is required, the range
chart should be confronted to be sure that the new pump fits into the
overall planning.
Many old pump lines have poorly planned range charts, resulting in
similar pump overlaps and uncovered gaps between pump sizes. Such a