Page 103 - Practical Machinery Management for Process Plants Major Process Equipment Maintenance and Repair

88 Major Process Equipment Maintenance and Repair

cooling. The load-carrying ability of bowl bearings is enhanced by the
Lomakin effect which is a function of the magnitude of the differential
pressure across the bearing and is explained in detail in Reference 4. Un-
less the product being pumped contains foreign material, these bearings
are best designed without spiral or axial grooves. Grooves interfere both
with the Lomakin effect and with the hydrodynamic load carrying ability
of the bearings.

Product Lubricated Column Bearings should have spiral or axial
grooves to provide proper cooling because they generally are not subject
to differential pressure.
Grease Lubricated Column Bearings should have axial grooves.
Oil Lubricated Column Bearings should have spiral grooves to provide
a downward pumping action.
Prelubrication of Column Bearings that are installed above the water
level in a deepwell or circulating pump is necessary. It can be achieved
by oil or grease lube, by fresh water injection from a source other than
the pump discharge, or by prelube piping around the check valve in the
discharge piping of a deepwell pump.
The bottom case or suction bell bearings in deepwell turbine pumps
and circulating water pumps are usually lubricated by a heavy non-
watersoluble grease which when installed in a properly designed bearing
housing with a large grease reservoir will last until the pump needs to be
dismantled for other reasons (Figure 2-13). These bearings should be in-
spected and repacked during routine maintenance. The bearing grooves
and grease reservoir should be filled completely and the grease plug rein-
stalled so that the bearing is dead-ended and the grease will not wash out.
Tension nut bearings should have oil or grease lubrication or injection
of pumped product that has been passed through a filter or a cyclone sep-
arator. Cyclone separators are inexpensive and reliable, provided that no
large solid particles are in the product, there is a large density difference
between the liquid and the solids, and the orifice does not erode out.

Avoidance of Wear Rings

Semi-open impeller designs should be utilized whenever possible so
that wear rings are avoided. If wear ring repair costs are excessive, com-
plete bowl assemblies of closed-impeller construction may be replaced
by semi-open impeller bowl assemblies after design review by the pump
manufacturer. This review should include determination that the driver
thrust bearing is adequate and that the coupling can be replaced with one
that is axially adjustable. The initial efficiency of semi-open impeller