necessary information on disassembly of the unit,
following table is a description of some of the
dimensions of the wearing rings, and reassembly
problems you will have to deal with together with
of the pump is specified by PMS or can be found
the probable causes:
in the manufacturer's technical manual. Failure
to replace the casing wearing ring when the
allowable clearance is exceeded results in a
decrease of pump capacity and efficiency. If you
have to disassemble a pump because of some
internal trouble, check the wearing ring for
clearance. Measure the outside diameter of the
impeller hub with an outside micrometer and the
inside diameter of the casing wearing ring with an
inside micrometer; the difference between the two
diameters is the actual wearing ring diametric
clearance. By checking the actual wearing ring
clearance with the maximum allowable clearance,
you can decide whether to renew the ring before
reassembling the pump. The applicable MRCs are
a readily available source of information on
proper clearances.
Wearing rings for most small pumps are
carried aboard ship as part of the ship's repair
parts allowance. These may need only a slight
amount of machining before they can be installed.
For some pumps, spare rotors are carried aboard
ship. The new rotor can be installed and the old
rotor sent to a repair activity for overhaul.
Overhauling a rotor includes renewing the wearing
rings, bearings, and shaft sleeve.
Operating Troubles.--You will be responsible
for the maintenance of centrifugal pumps. The
Figure 7-7.--Impeller, impeller wearing ring, and casing
wearing ring for a centrifugal pump.
7-7