Page 219 - Know and Understand Centrifugal Pumps

Failure Analysis

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Seals

Causes of premature seal failure

There are numerous reasons why seals fail prematurely. The origin of
the failure can reside in the pumping system, in the pump operation, or
the maintenance shop, the storeroom, or even before the seal arrived
into the plant. The first sign of failure normally is liquid on the floor.

It’s possible that a failure occurred to the seal at the manufacturer.
Nowadays, the companies that we call ‘Manufacturers’ or ‘Factories’ are
actually ‘Parts Assemblers’. It’s likely that no mechanical seal
manufacturer is really fabricating their springs, seal faces, or set screws.
These ‘Assemblers’ contract other companies to fabricate the pieces.
The failure could have originated in the moment that a sub-contractor
made a piece. The failure could have originated on the seal assembly
line. The majority of the ‘Seal Assemblers’ would perform a static
pressure and vacuum test on their final product. It’s unlikely that they
would perform a dynamic pressure and vacuum test on their creations.
So if an anti-rotation pin were left out at the factory, it’s likely this
would not be identified until the seal and pump are started. And
although these ‘Assemblers’ don’t want to admit it, there are actually
deficient seal designs being delivered to the customers that simply don’t
work.

The storeroom techs must protect the mechanical seals handling them
with extreme care. The engineer or technician must specify and select
the seal components correctly. The mechanical maintenance technician
must protect the seal at the moment of installation. Once the seal is
installed into the pump, the seal requires the correct environmental
controls to assure optimum life. At this point the work of the
maintenance technician ends.
We could say that if the mechanical seal fails immediately, or within
moments of the pump start-up, one should investigate the events

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