5
D3: Removing the Rotating Assembly
The complete rotating assembly, comprising the impeller, shaft,
shaft sleeves and bearings may be lifted out as a single unit.
Release the bearing bracket bolts, and use a soft sling around the
exposed parts of the shaft to lift the rotating assembly clear.
(See Figure 8.)
D4: Removing the Impeller
Strip the shaft of its bearings and shaft sleeves to allow the
impeller to be withdrawn from the shaft. Note the direction of the
impeller vanes, so that the impeller may be re-assembled in the
correct rotational direction.
Impeller passages should be free from debris. Check for cavita-
tion damage to the eye of the impeller, where the liquid enters.
Cavitation is caused when there is insufficient suction pressure to
the pump. Pitting or spongified surfaces to the impeller vanes
may be seen.
D5: Removing the Mechanical Seal
The mechanical seal (if fitted) may be removed without lifting the
top half casing. The bearing bracket must first be removed, by
detaching the bearing covers and releasing the bearing from the
shaft. The bearing bracket will now slide off the shaft horizontally,
providing access to the mechanical seal glandplate. Withdraw
the glandplate nuts and remove, to reveal the mechanical seal.
D6: Mechanical Seal Problems
Mechanical seals will fail if allowed to run dry. This can occur
even if the pump is seemingly full of liquid, if a vapor pocket
builds up in the seal area.
Pumps operating on hot water duties are particularly prone to this
failure, if the static pressure in the system is insufficient to prevent
local vaporization. Failure of a seal may also indicate worn bear-
ings, hence it is good practice to inspect and if necessary replace
the shaft bearings when a seal is changed.
D7: Fitting a New Casing Wear Ring
The casing is provided with wear rings which may be replaced
after prolonged service, to restore the close clearances with the
impeller. The standard clearance for a new pump is 0.4-0.5 mm
diametrically, between the bore of the wear ring and the outside
diameter of the impeller neck.
The efficiency of the pump will deteriorate as the clearance
increases through normal wear. To extract the casing wear ring, it
will be necessary to remove the top half casing and rotating ele-
ment as described earlier. When replacing the wear ring, be sure
to thoroughly clean the casing seating, as the wear ring must be
positioned concentrically upon reassembly.
D8: Casing Gasket
Whenever the top half casing is removed, the casing gasket should
be replaced. If a gasket is cut on site, ensure that the gasket paper
used is of the correct thickness, and that the gasket material is
compatible with the liquid being pumped. It is good practice to
leave extra gasket material in the glandplate sealing area, to be
trimmed off once the top half casing is fully bolted down.
GLANDPLATE
CASING SPLIT
FLANGE NUTS
Figure 7
IMPELLER
BEARING
BRACKET BOLTS
SHAFT
Figure 8