can be installed. On others, the shaft sleeve may
The packing in centrifugal pump stuffing
have a snug slip-on fit, butted up against a
boxes (fig. 7-6) is renewed following the PMS.
shoulder on the shaft and held securely in place
When replacing packing, be sure to use packing
with a nut. On smaller pumps, you can install new
of the specified material and the correct size.
sleeves by removing the water end casing,
Stagger the joints in the packing rings so they fall
impeller, and old shaft sleeves. New sleeves are
at different points around the shaft. Pack the
carried as repair parts; they can also be made in
stuffing box loosely and set up lightly on the
the machine shop. On a large pump, the sleeve
gland, allowing a liberal leakage. With the pump
is usually pressed on; the old sleeve must be
in operation, tighten the glands and gradually
machined off before a new one can be pressed on.
compress the packing. It is important to do this
You must disassemble the pump and take the
gradually and evenly to avoid excessive friction.
sleeve to a machine shop, a repair shop, or a naval
Uneven tightening could cause overheating and
shipyard to have this done.
possible scoring of the shaft or the shaft sleeve.
To prevent water leakage between the shaft
On some centrifugal pumps, a lantern ring is
and the sleeve, some sleeves are packed, others
inserted between the rings of the packing. When
have an O-ring between the shaft and the
repacking stuffing boxes on such pumps, be sure
abutting shoulder. For detailed information,
to replace the packing beyond the lantern ring.
consult the appropriate manufacturer's technical
The packing should not block off the liquid seal
manual or applicable blueprint.
line connection to the lantern ring after the gland
has been tightened.
Renewing Wearing Rings.--The clearance
Figure 7-6 shows how the packing is arranged.
between the impeller and the casing wearing ring
Notice how the lantern ring lines up with the
(fig. 7-7) must be maintained as directed by the
liquid seal connection when the gland is tightened.
manufacturer. When clearances exceed the
specified amount, the casing wearing ring
Renewing Shaft Sleeves.--In some pumps the
must be replaced. On most ships, this job
shaft sleeve is pressed onto the shaft tightly by
can be done by the ship's force, but it requires
a hydraulic press. In this case, the old sleeve must
the complete disassembly of the pump. All
be machined off with a lathe before a new one
Figure 7-6.--Stuffing box on a centrifugal pump.
7-6
