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The Practical Pumping Handbook

5. Practical knowledge of pump design.
6. Component inspection equipment and techniques.
7. Sound repair techniques.
8. Practical machining skills.
9. Access to a well equipped and clean repair facility with quality
machining and balancing equipment.
10. Established acceptance criteria.

12.1.2 Economic considerations
It is important to remember, before any repair procedures are
performed on any pump component, that the material of construction
must be accurately identified by means of the appropriate tests. It is also
advisable to consider the economic advantage of the repair under
consideration.

Smaller and medium-sized ANSI pumps are designed with a high
degree of interchangeability and produced in volume. Consequently, it
can frequently be more cost effective to replace the entire pump rather
than a combination of the impeller, casing and back cover. In addition,
both the individual parts and complete pumps are available fairly
quickly. This can make it more cost effective to replace rather than
repair the parts, unless the wet ends are made of the more exotic alloys.
It is clear, in the case of non-metallic pumps, that the components must
be replaced, as they generally cannot be repaired.
API pumps, however, are generally more economical to repair than to
replace. These units are usually installed in more rugged duties and
hazardous applications in refineries or other petrochemical industries,
and are consequently more durable and more expensive. Delivery
periods are also frequently longer, and the parts more costly than their
ANSI equivalents, particularly the cases and impellers.

This makes it very tempting to source these parts from an after-market
supplier rather than the Original Equipment Manufacturer (OEM).
However, it should be noted that the major parts of a centrifugal pump
(i.e. the casing, the impeller and the back cover) are all cast from
patterns involving highly engineered hydraulic designs, which arc of a
proprietary nature. These parts are also the ones that provide the
hydraulic performance of the pump. While the parts might be available
from after-market suppliers at slightly lower prices than they are from
the OEM, that cost saving will fade into insignificance if the pump does
not meet its hydraulic performance. The OEM can accept the
responsibility for the subsequent hydraulic performance of these
replacement parts.

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