Page 336 - Centrifugal Pumps 2E

Chemical Pumps Metallic and Nonmetalfic 301

Clamping Between the Housing and End Cover

With this type of a mount (Figure 15-11), there are fewer tolerances
and fits to cause misalignment than when used in a separate end cover.
However, to obtain axial adjustment, the end cover has to be removed to
add additional shims to either side of the snap ring to obtain the impeller
clearance. This will require a complete shut down of the pump and disas-
sembly of the end cover.

End Cover Mount

The end cover is a separate piece that slides within the bearing housing.
The end cover has an O-ring to prevent oil leakage from the housing. The
fit between the end cover and the bearing housing bore is .001 to ,002
inches. Expertise is required in machining of the end cover with auto-
matic machines that can exert excessive jaw pressure. This will cause
distortion resulting in incorrect bearing fits. The end cover has an oil re-
turn passage line that can be either cast or machined so oil can flow back
into the reservoir.
The bearing is held in the end cover by a snap ring, a lock ring, or a
solid ring (Figure 15-12A). When using snap or spiral flex rings, care
has to be taken that the radius dn the outer race of the bearing is main-
tained within the tolerance. If this radius is too large, the axial load will
concentrate on the inner diameter of the snap or circle ring causing it to
deflect in a cantilever action reducing the clearance between the impeller
and the casing.
A solid ring is used to prevent this problem. The solid ring is either
threaded into the bearing end cover or screwed on with a series of small
bolts (Figure 15-12B). Axial adjustment of the impeller to casing is ob-
tained by two sets of three bolts. One set of bolts is threaded into the end
cover so that when they are turned they go against the bearing housing
causing the end cover to move back toward the coupling. The other set is
screwed into the bearing housing so when they are tightened and the oth-
ers are loosened the end cover goes toward the impeller.

End Sealing

Ends of the bearing housings have to be sealed to prevent external liq-
uids from entering into the housing as well as oil from leaking out. This