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have little or no lubricant in the immediate area of the lip seals, thus
contributing to their early failure. In addition, the lip seal is a contact
seal that will inevitably groove the shaft.

7.9.3 lhe magnetic seals
This is a mature design whose use in centrifugal pumps has been
recently reintroduced as an option to the lip seal. A current double seal
design brings the rotating faces into full contact with the stationary
magnet to completely seal off the housing.

7.9.4 Bearing isolator
A less damaging option is a non-
contacting labyrinth seal or
bearing isolator, and these are
available in a variety of con-
figurations. All of them have a
rotor secured to the shaft by 'O'-
rings that drive the rotor without
inflicting any fretting damage. The
stator collects the liquid
centrifuged away from the rotor,
and drains it away from the
lubricant to the outside of the
housing.
Most of these seals are designed to
operate on horizontal shafts with a
drain hole that is required to be Figure 7.19: Bearing isolator (Reproduced
installed at the lowest (or six with permission of Inpro/Seal Company)
o'clock) position.
Earlier designs exposed the inside of the bearing housing to external
ambient conditions when the pump was not running. While this was
acceptable in many instances, in areas of high humidity it permitted the
ingress of sufficient moisture to perpetuate the problem. To combat
this, some bearing isolator designs are now available that will seal off
the housing when the pump is stationary. Under these conditions it
would be advisable to seal off the traditional breather cap.

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