Centrifugal Pumps Design and Application 2nd ed - Val S. Lobanoff, Robert R. Ross (Butterworth-Heinemann, 1992)

Rolling Element Bearings and Lubrications 551
Figure 20-18. "Bearing isolators" are non-contacting bearing housing seals
which are sometimes used in centrifugal pumps (courtesy of INPRO Seal Company,
Rock Island, Illinois).
nents as shown in Figure 20-19. These components are: (1) a magnetized
ring, having an optically flat sealing surface that is fixed in a stationary
manner to the housing and sealed to the housing by means of a secondary
O-ring, and (2) a rotating ring having a sealing surface that is coupled to
the shaft for rotation and sealed to the shaft with an O-ring.
The rotating ring, which is fabricated from a ferromagnetic stainless
steel, can be moved along the shaft. When no fluid pressure exists, the
sealing surfaces are held together by the magnetic force, which is reliable
and uniform, creating a positive seal with minimum friction between the
sealing faces and ensuring the proper alignment of the surfaces through
the equal distribution of pressure.
Magnetic seals are very reliable. Many have operated continuously for
40,000 hours without repair or adjustment under conditions considerably
more severe than those to which chemical process pumps are typically
exposed.
Finally, if sealed-bearing housings must accommodate changes in internal
pressure and vapor volume, an expansion chamber similar to that
shown in Figure 20-20 can be used. This small device, which incorpo-