Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The invention relates to a stuffing box assembly and
especially to soft-packed seals suitable for use in sealing
pumps, mixers, compressors, valves and the like.
The traditional practice in sealing machinery subject
to fluid leakage is to arrange that shafts or the like project
from the machinery through a cylindrical housing. The sealing
arrangement is then disposed in the annular space between the
housing and the shaft, being`essentially in sealing connection
with both the shaft and the housing. More specifically when
soft packing is used as the sealing means, the annular space
is filled with soft packing and its associated spacing pieces
and adaptors, said soft packing being in contact with both the
bore of the housing and of the shaft. The packing i5 then
loaded by means of an adjustable gland plate positively posi- -
tioned relative to the face of the housing. An axial loading
is produced in the packing in the direction of the axis of the
shaft and housing. The packing is then deformed by the axial
load both axially and radially so that the existing contacts
between the packing, housing bore and shaft become sealing `
~0 contacts resisting the tendency of fluid to leak from the
machinery. The disadvantages of the conventional soft packed
stuffing box outlined above are uneven loading in the axial
length of the packing, difficulties in the replacement of the `
packing and where the shaft revolves, uneven shaft wear and
frequent ad~ustment of the gland plate.
It has been proposed to provide a soft packed seal of
a radially-loaded nature, the radial loading being effected by
a fluid medium.
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: However, the construction of seal employed in such
proposal is difficult to instal and the loading fluid distri-
bution is non-uniform, and it is an ohject of the present
invention to obviate or mitigate these drawbacks.
According to the present invention there is provided
a stuffing box assembly comprising a shaft rotatably mounted
within a housing, a soft packing formed as a cylindrical sleeve,
surrounding the shaft, an encapsulating flexible elastomeric
cylindrical imperforate carrier surrounding the soft packing
and having at each end an inturned end flange abutting the
adjacent end of the soft packing, a rigid sleeve surrounding
the flexible carrier in contiguous relationship therewith,
spaced formations on the cylindrical surface of the flexible
carrier to define therebetween and the rigid sleeve a passage-
way for dispersion over the surface of the flexible carrier of
a loading fluid, and axially spaced radially extending holes ;
in said soft packing for penetration of a fluid to be sealed
into the soft packing.
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The soft pac~ing and flexible carrier may be diamet-
rically split in an axial direction.
The sealing means according to the present invention
permits a uniform radial loading of the packing; a reduction in
the frequency of adjustment of the packing; standardisation of
the paclcing arrangement for a given size of shaft or other
determining factor; easier adjustment; and simpler replacement ~ -
of a worn packing.
An embodiment of the present invention will now be
described by way of example, with reference to the accompanying
drawing, in which: -
Fig. 1 is a diagrammatic section of a stuffing box
assembly suitable for use with a pump; -
Fig. 2 is a fragmentary view of a modification of the
stuffing box assembly shown in Fig. 1. ``
In Figure 1, the stuffing box assembly comprises a ~;
pump shaft 1 surrounded by a housing 2. It is desired to pre-
vent leakage of fluid through the annular
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space 3 between the housing 2 and the shaft 1 which is rotatable.
A packing 4 of, for example, an asbestos composite is arranged
around the shaft 1 and is encapsulated in a carrier 5 of a flex- -
ible nature. The packing 4 may be preformed to a cylindrical
shape and may consist of a single component or be split along
the axis of the shaft to provide two or more components. Simi-
larly, the carrier 5 is axially split to match the packing 4 and
is constructed of an elastomeric flexible material, such for
example, as synthetic rubber. The carrier 5 is also provided
with circumferential and/or axial pro~ections 6, grooves or -
other arrangements on its outer circumferential surface to faci-
litate distribution or dispersion of a loading fluid. The
carrier 5 is located in a metal sleeve 7 against an inwardly
turned lip 8.thereof at the fluid or inner end, the sleeve 7
being in contiguous contact with the carrier 5 along its inner
diameter. The radial thickness of the sleeve 7 is so arranged
that it is easily accommodated within the annular space 3. The
sleeve 7 may alternatively or additionally be provided loading ;;
fluid dispersion arrangements.
The sleeve 7 is of greater length than the carrier 5
and has a radially outwardly directed flange 9 at its outer end.
The flange 9 is sealed against the face of the housing 2 by a ;
gasket 10, and is held in position by a gland plate 11, an '0'-
ring 12 being interposed between the gland plate 11 and flange
9. The sleeve 7 may, if desired, be located on the gland plate
11 by a spigot arrangement for ease of location and fitting.
Alternatively, the spigot arrangement may be omitted and the
carrier 5 may be the same length as the plate 7, the packing
4 being appropriately dimensioned.
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The gland plate 11 is held positively in relation to the housing
2 by retaining bolts 13 or similar, and is arranged to project
into the sleeve 7 so that it is in abutment with the carrier 5
as indicated at 14. A passageway 15 is arranged in the gland -
plate 11 to facilitate the transfer of a loading fluid from a
convenient point on the gland plate to the annular space 16
between the sleeve 7 and the carrier 5. Several such passageways
may be arranged between this annular space and convenient points -~
on the gland plate. One of the passageways 15 is provided with
a pressure relief valve 17 to prevent overload of the assembly.
It is preferred that the relief pressure of the valve 17 be set
to a value that is close to and slightly in excess of the loading
fluid pressure.
~ In Figure 2, a series of axially and circumferentially
spaced holes 4A are provided which extend radially through the
packing 4 to prevent undue pressure build up and permit a free
transfer-of fluid from the shaft area into the packing. Similarly,
a series of axially and circumferentially spaced holes 5A are
provided which extend radially through the carrier 5. These
holes 4A and/or 5A prevent undue pressure build up between the
carrier 5 and the packing 4, for example, due to heat, and, when
the holes 4A and 5A are both provided, allow access of the
loading fluid from the annular spaces 16 to the interface between
the carrier 5 and the packing. However, in accordance with the
invention, only the holes 4A are provided.
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In operation, the loading fluid, for example grease or
hydraulic fluid, is injected into the passageway 15 or one or
more thereof under pressure. The fluid flows into the annular
space 16 between the sleeve 7 and the carrier 5 being uniformly
dispersed around the outer diameter of the carrier 5. In the -
embodiment in accordance with the invention, i.e. when holes 5A ~
are not used, leakage of the loading fluid is sufficiently pre- -
vented by the radial sealing effect of the sleeve 7 and the
gland plate 11 with the end faces of the carrier 5. The pres-
sure of the loading fluid is transmitted vla the carrier 5 to
the packing 4 and the shaft 1. As the pressure is evenly dis- -
tributed over the carrier 5 then the pressure between the shaft
1 and the packing 4 is substantially uniform over the contact
area of the packing.
Replacement of the packing 4 is by way of loosening
bolts 13, sliding the gland plate 11 away from the housing 2
and then extracting the sleeve 7 with the packing 4 and carrier
5 within it. Having relocated the packing 4 and carrier 5 exter-
nal to the housing 2 the sleeve 7 may then be returned into the ~-
housing 2, a~ the used packing 4 and carrier 5 having been
removed from the shaft 1 and been replaced by a similar unused
set. The sleeve 7 is then returned over the packing 4 and
carrier S and the entire unit relocated by returning the gland
plate 11 to its ori~inal position, finally retaining the assembly
by the bolts 13. Throughout the replacement operation care must
be taken to ensure that the seal 12 and gasket 10 are not dam~
aged and are satisfactorily repositioned.
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Tt will be appreciated that the above arrangemen~
of packing assembl~ is b~ way of example and other arrangernents
, of simila~ nature, utilisin~ the basic packing and carrier
arrangement can be desi~ned.
In a modirication, the sleeve 7 and its fl~nges
8 and 9 are oinitted, the interior of the pump housin~ 2 being
suitably configured to take the place, and serve the function,
of the plate 7.
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