start-up process for pumps can be a critical time when problems
arise with the mechanical seals they contain. The pump manufacturers
do not necessarily give instructions on the right procedures to
follow to protect the mechanical seals when the pumps are turned
on and the seals can be ruined if the proper steps are not followed.
For example, most pumps are self-venting but that does not mean
that the stuffing box area is vented. To make sure the mechanical
seals do not run dry, the stuffing box must be relieved of air.
a pump in a critical application will be hooked up to a stand-by
pump in case there is a problem. However, if the mechanical seals
in the stand-by pump are not made from the right elastomer, they
could have a tendency to harden, distort their shape or stick
to the shaft if the pump is not used for a long period of time.
Obviously, then when the stand-by pump is needed and turned on,
the mechanical seals in it will fail.
you have mechanical seals that have failed, it is important to
look at them to determine what caused the failure. There are many
factors that cause failure:
Degradation: The mechanical seals may exhibit many signs of
degradation including blisters, cracks, voids or discoloration.
It may be honey combed, flaky or starting to crumble. In some
cases, the degradation is observable only by measurement of
or Nibbling: The mechanical seals develop ragged edges (generally
on the low-pressure side) which appear tattered.
Degradation: The seals may exhibit radial cracks located on
the highest temperature surfaces. In addition, certain elastomers
may exhibit signs of softening - a shiny surface as a result
of excessive temperatures.
Fretting Corrosion: This causes leakage at the secondary seals
and will cause problems with the sleeve directly beneath the
secondary seal area. This area will be pitted and shiny.
Vaporization: You will see places on the seal faces where vapor
was blown out. There will be chipping on the inside and outside
diameters and the whole area will be pitted.
& Coking: The mechanical seals will have a film or sludge
on the side that is exposed to the atmosphere. This not only
can lead to the seal faces wearing quicker than usual, but it
can cause the seals to want to hang up.