Page 184 - Know and Understand Centrifugal Pumps

Bearings

will be consistent with inadequate lubrication.

Sometimes bearings seem to run hot at pump start-up. This may be
heat actually generated by the bearing seals and not the bearings or
inadequate lubrication practices. After the seals seat and settle, the
temperature should go back to normal.

Bearing seals

The mechanical seal for bearings
Among the newer developmcnts for industrial pumps is the bearing
mechanical seal (Figure 11-3). These seals are designed to run in the
same space provided for lip and labyrinth seals. There are two basic
concepts to designing these seals. One concept incorporates rotary and
stationary faces held together with spring tension like standard process
pump seals. The other basic concept utilizes magnets to hold the faces
together. The flexibly mounted faces permit a small degree of axial and
radial movement of the shaft without compromising the sealing ability.
These seals perform well to completely separate the environment inside
the bearing chamber from the environment outside the bearing
chamber. These seals have proven effective in retaining grease and oil
and especially the oil fogs (described earlier in this chapter) inside the
bearings. By holding positive pressure, neither contaminants nor
humidity can enter into the bearings. It is rccomrnended to close and
plug the breather cap, or to use this port to install humidity,
temperature and level sensors to monitor the bearings.

Figure 11-3
~
167 I