Page 244 - Know and Understand Centrifugal Pumps

Common Sense Failure Analysis

develop a correct parts inventory that is based on actual parts
consumption and not on recommended parts provided by the
manufacturer. The frequent replacement of worn parts can indicate a
possible substitution of materials from the original OEM part.
Record keeping is critical in those industries whose production requires
the use of many pumps. The record of the pump should have the
complete information on the installation, application and maintenance.
Space should be provided in each card, using both sides, to keep a
complete record during a two-year period, and in some cases, for the
whole life of the pump.

Failure analysis on centrifugal pumps
~~
Many times, the broken part of a pump is replaced when it fails without
an effort to understand why the situation happened. Any corrective
action that takes place is usually a temporary arrangement. The
probability is quite high that the pump will fail again for the same
reason. This part replacement with no analysis practice is not acceptable
due to the high cost of the maintenance, parts, time and lost
production.
It is interesting to note that some pump users literally know that their
pumps will fail after a specific time period. They understand that the
running time of the pump should be maximized to have an acceptable
yield in the process. This type of strategy is expensive since it raises a
doubt of the continuity of the pump performance. To compensate,
some plants install back up or redundant pumps.
In order to solve a pump failure, we have to identify the cause. Once
this is known, the problem can be dealt with and a permanent solution
can be found. A logical thought process (common sense) to identify the
problem is as follows:

1. Ask ‘What’s making this happen?’ - It is likely that what we call the
problem is actually the symptom. Example: ‘Low discharge
pressure’, ‘failed mechanical seal’, ‘the pump makes noise.’

2. Look for the evidence - The evidence is the manifestation of the
symptoms. The evidence indicates that there is a problem with the
pumping system. Example: ‘the discharge gauges indicate a low
pressure’.
3. Verify evidence - Example: ‘Is the gauge calibrated and accurate?’
Eliminate or cancel other reasons or possibilities for the evidence.
Example: ‘The pump is not pumping enough pressure and we’re no
longer able to fill that tank.’

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