Page 186 - Know and Understand Centrifugal Pumps

Bearings

Most commercial models will ride into the same radial space provided
for earlier lip seals. They may require some additional axial space on the
pump shaft, but this normally doesn’t interfere with other obstructions
or equipment. Even if pump modification is required to accommodate
the labyrinth seal, it is an improvement over the lip seal. Remember that
the bearing housing was first bastardized to accommodate the lip seal.
Any hrther modification to accommodate the labyrinth seal will not
affect the service of the pump.
Labyrinth seals work best when the pump is running. Centrifugal force
favors the labyrinth seal’s action. Earlier models were only specified for
horizontal pump shafts. Later models are designed for both horizontal
and vertical pump shafts and effectively perform their function whether
the pump is running or off.

The lip seal
The lip seal, or oil seal, used on modern centrifugal pumps is borrowed
from the automotive industry. The lip seal was born with the invention
of the automobile transmission and the universal joint in the early days
of the family car. It would effectively retain the transmission fluid and
U-joint grease on jalopies with rumble seats. It really hasn’t changed
much in design since the 1920s.
The outside diameter of the lip seal fits and seats into the housing bore
(transmission or pump). The inside diameter, with the elastomeric lip,
rides onto the spinning shaft (whether vehicular drive shaft or pump
shaft).

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Fiaure 11-5

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