Page 173 - Know and Understand Centrifugal Pumps

Know and Understand Centrifugal Pumps

TYPE DESCRIPTION

Ball Bearing - Double Row, self-aligning These bearings have two rows of balls
and they can handle some shaft
misalignment. The axial or thrust
loading is limited.
Ball Bearing - Angular Contact These are single row ball bearings
capable of handling extreme axial or
thrust loads in one single direction only,
They are generally mounted in pairs to
handle any opposite axiallthrust loads.
Roller Bearing - Cylindrical This bearing is best suited to handle
radial loads. It doesn't work well with
axiallthrust loads. This bearing is
popular in electric motors.
Roller Bearing - Conical These bearings are good handling
extreme axial / thrust loads in one
single direction only.
Roller Bearing - Needle These are a type of roller bearing with a
roller diameter normally less than .250"
and about a 1 :6 diameter to length
ratio, thus the term needle.
Roller Bearing - Spherical Symmetrical These spherical rollers are barrel shaped
and mounted in two rows rolling inside
a common inner and outer race
housing.

Each type of bearing is manufactured with different classifications of
play or internal tolerance. This play or tolerance refers to the distance
between the surface of the balls or rollers and the internal and external
raceways with axial or radial movement. The bearing tolerance is rated
with the codes C1, C2, CN, C3, C4 and C5. CN code is the normal,
standard or average precision. C1 is the most precise tolerance (the
tightest) bearing and C5 is the least precision tolerance (the loosest)
bearing. A bearing without a stated code is normally a CN rating.
Standard pump bearings are mostly C3 or higher, slightly forgiving and
loose. With this understanding of pump bearings, you can see that it is
not convenient to replace a C3 pump bearing with a C1 bearing.
Because of its strict tolerance, a C1 bearing can handle less thermal
expansion and lubricant contamination that occur with normal pump
operation. A C1 bearing is less forgiving with thermal expansion and
contamination and will fail prematurely.

As we've seen in previous chapters, the pump has basic head and flow