The operating manual of any centrifugal
pump often starts with a general statement, “Your centrifugal pump will give
you completely trouble free and satisfactory service only on the condition that
it is installed and operated with due care and is properly maintained.” Despite
all the care in operation and maintenance, engineers often face the statement
“the pump has failed i.e. it can no longer be kept in service”. Inability to
deliver the desired flow and head is just one of the most common conditions for
taking a pump out of service. There are other many conditions in which a pump,
despite suffering no loss in flow or head, is considered to have failed and has
to be pulled out of service as soon as possible. These include seal related
problems (leakages, loss of flushing, cooling, quenching systems, etc), pump
and motor bearings related problems (loss of lubrication, cooling,
contamination of oil, abnormal noise, etc), leakages from pump casing, very
high noise and vibration levels, or driver (motor or turbine) related problems.
The list of pump failure conditions mentioned above is neither exhaustive nor
are the conditions mutually exclusive. Often the root causes of failure are the
same but the symptoms are different. A little care when first symptoms of a
problem appear can save the pumps from permanent failures. Thus the most
important task in such situations is to find out whether the pump has failed
mechanically or if there is some process deficiency, or both. Many times when
the pumps are sent to the workshop, the maintenance people do not find anything
wrong on disassembling it. Thus the decision to pull a pump out of service for
maintenance / repair should be made after a detailed analysis of the symptoms
and root causes of the pump failure. Also, in case of any mechanical failure or
physical damage of pump internals, the operating engineer should be able to
relate the failure to the process unit’s operating problems. Any operating
engineer, who typically has a chemical engineering background and who desires
to protect his pumps from frequent failures must develop not only a good
understanding of the process but also thorough knowledge of the mechanics of
the pump. Effective troubleshooting requires an ability to observe changes in
performance over time, and in the event of a failure, the capacity to
thoroughly investigate the cause of the failure and take measures to prevent
the problem from re-occurring.
This material was obtained from: http://www.plant-maintenance.com/articles/centrifugalpumps.pdf
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