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To
achieve zero leakage between a moving member and a
relatively stationery part, a wide range of seals
and rings are employed. However, the most common,
least expensive and versatile in nature is the Gland
Packing. It provides a dynamic seal for a rod, shaft
or stem via a housing or gland which is packed with
resilient or semi-resilient material, thus providing
a localised contact area which offers a physical
barrier to leakage Properties the Gland packing must possess -
Good Anti-Friction Properties
-
Good
chemical resistance to fluid contained
Should
not get effected by the temperature of
application
-
Should
be reasonably compressible and have a good
resilienc
Should
retain the self lubricants
Should
not effect the shaft
-
Should
not contaminate the fluid being contained
Gland
packing is not an exact science as its performance
depends upon many variables. The filling of a
packing is an art and results depend largely on
manual skills. The 'Man with a Wrench' therefore,
can sometimes. be a dangerous person in your plant,
responsible for scored rods, excessive downtime and
wasted packing. Condition
of Plant: To
ensure long and trouble free sealing, check the
following periodically: The
clearance between shaft and neck-bush at the
bottom end of the stuffing box. The maximum
normal clearance is 0.25mm.
-
Concentricity
of shaft with stuffing box bore.
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Straightness
of shaft (run-out)- not to exceed 0.5mm. Clock
gauge reading
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Condition
of shaft surface in packing area-no excessive
grooves, scores or pitting
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Pump
Bearings--wear can induce shaft "whip"
which can be harmful to packings.
Packing
the GLAND -
Ensure
that all the old packing is removed and the
stuffing box is clean and free from foreign
matter.
-
Always
re-pack with new packing
Select
correct size of packing to fit the stuffing box dimensions -
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Wrap
packing on the shaft and cut into rings of
correct size
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Fit
each packing individually by tamping or with
split sleeves
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Stagger
joints in consecutive packing rings
Fit
gland follower and check that the shaft rotates
freely
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Tighten
gland nuts evenly with spanner until the package
"drags" when turning the shaft
by hand.
-
Valves-pressurise
the stuffing box and if necessary re-adjust the
gland nuts evenly until a leak-free seal is
obtained.
-
Pumps-Slacken
the gland nuts back and re-tighten to finger
tight, to such an extent that the shaft still
rotates freely.
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