AU5140698A

AU5140698A - Dynamic packing type seal

Info

Publication number: AU5140698A
Application number: AU51406/98A
Authority: AU
Inventors: Ganesh Murugan
Original assignee: Individual
Current assignee: Individual
Priority date: 1996-12-02
Filing date: 1997-12-02
Publication date: 1998-06-29
Also published as: WO1998025056A1

Description

DYNAMIC PACKING TYPE SEAL

This invention relates to seals, and in particular to dynamic seals for sealing about rotating members such as shafts.

Prior art dynamic seals, such as packing seals, are known which have a stuffing box surrounding the rotating shaft. The shaft passes through a closely toleranced opening at one end of the stuffing box. At the other end of the stuffing box a gland encloses the packing space. The gland is often bolted to the stuffing box. The gland includes an opening which is closely toleranced to the shaft, allowing the shaft to pass through the stuffing box. The packing space is filled with a packing material. The packing material varies according to the application and working conditions, but vegetable materials such as cotton fibres are commonly used. Tightening of the bolts fixing the gland to the stuffing box will increase the axial pressure against the packing material. This creates a corresponding increase in the radial pressure in the material. The radial pressure of the material against the shaft effects the seal. As such systems rely on axial pressure to increase the radial pressure, the efficiency of this sealing, in comparison with the forces exerted by the gland, is governed by the Poisson's ratio for the material. Good packing materials, which have durability and high heat transfer characteristics, tend not to have a good Poisson's ratio. It is an object of the present invention to provide a dynamic seal which will at least go some way towards overcoming the above disadvantage or will at least provide industry with a useful choice.

In one aspect the invention consists in a dynamic seal comprising: a gland housing, a shaft means passing through said gland housing and having an annular base thereon extending substantially perpendicularly from the axial surface of said shaft means, a gland follower, an annular stuffing cavity surrounded by said gland follower, said gland housing, said perpendicularly extending annular shaft means face and said axial shaft means surface, the volume of said cavity adjustable by movement of said gland follower, and packing in said stuffing cavity, such that when under compression from said gland follower dynamic seal faces are induced at the interface between said packing and said shaft means axial surface and at the interface of said packing and said perpendicularly extending face.

To those skilled in the art to which the invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention as defined in the appended claims. The disclosures and the descriptions herein are purely illustrative and are not intended to be in any sense limiting.

Preferred forms of the present invention will now be described with reference to the accompanying drawings in which;

Figure 1 is a side elevation in cross section of a dynamic seal according to one embodiment of present invention, Figure 2 is a side elevation in cross section of part of a dynamic seal according to a second embodiment of the present invention,

Figure 3 is a side elevation in cross section of part of a dynamic seal according to a third embodiment of the present invention.

Figure 4 is a side elevation in cross section of part of a dynamic seal according to a fourth embodiment of the present invention.

Figure 5 is a side elevation in cross section of part of a dynamic seal according to another embodiment of the present invention, incorporating a double seal,

Figure 6 is a side elevation in cross section of part of a dynamic seal according to a sixth embodiment of the present invention, Figure 7 is an end elevation of the sleeve incorporated in the dynamic seal of

Figure 6, and

Figure 8 is a side elevation in cross section of a dynamic seal according to a seventh embodiment of the present invention.

With reference to Figure 1 a dynamic seal is shown generally referenced 1. The dynamic seal has a shaft assembly 3 which in the embodiment depicted in Figure 1 includes a shaft 2 and a sleeve 4 on the outside of the shaft. The sleeve 4 may be provided as it is less costly to replace when worn than the entire shaft. The shaft assembly 3 passes through a stuffing box 5 or gland housing. A packing space is defined by the interior surface 6 of the stuffing box, and by the exterior surface 8 of the shaft assembly. The packing space is in use filled with a packing material 7. At one end the shaft assembly passes out of the stuffing box through an opening

10 in the end 1 1 of the stuffing box. The shaft assembly 3 has a section 12 thereof having a diameter which is substantially larger than the diameter of the section 13 enclosed by the stuffing box 5 and surrounded by the packing space. The section 12 is disposed at the position where the shaft passes through the opening 10. The opening 10 is closely toleranced to the diameter of the section 12. The diameter of the opening 10 is slightly larger than that of the section 12, and a small clearance is allowed between the opening and the surface 16 of the section 12.

At the other end 20 of the stuffing box the packing space is left open, and is unrestricted by an "end". A gland follower 17 is provided which has a protruding portion 18 configured to be insertable into the packing space. The gland follower 17 has a bore 19 there through. The shaft assembly 3 passes through the bore 19 in the gland follower 17. The bore 19 is closely toleranced to the outside diameter of the section 13 of the shaft within the stuffing box, being slightly larger in diameter. The outside surface 21 of the gland follower 17 is closely toleranced to the interior surface 6 of the stuffing box, being slightly smaller. The packing space may have circular axial cross section or could be have any other axial cross section depending on the circumstance or application of the seal.

The protruding portion 18 of the gland follower 17 has an end face 22 which in use exerts pressure against the packing material 7 enclosed within the packing space. The gland follower 17 has a flange 25 extending outwardly at the end thereof which is outside the stuffing box 5. The stuffing box 5 may also include a flanged portion 27 at the end 20 thereof, the flange 27 extending outwardly. The stuffing box has an end face 26 which may include the flange 27. The flange 25 of the gland follower 17 overlaps the end face 26 of the stuffing box 5. The flange 27 of the stuffing box 5 is provided with a plurality of threaded holes 29. Bolts 30 pass through clear holes 31 in the flange 25 of the gland follower 17, and are threaded into the threaded holes 29 in the flange 27 of the stuffing box 25.

Tightening the bolts 30 draws the protruding portion 18 of the gland follower 17 further into the packing space of the stuffing box, thereby compressing the packing material 7. Compression of the material 7 in an axial direction will cause an increase in the radial compressive stress in the material in accordance with the Poisson's ratio of the material. It will also directly cause an axial compressive stress in the material which will be substantially greater than the radial compressive stress. The radial compressive stress will determine the effectiveness of the seal against the outside surface 8 of the shaft assembly 3. As shown in Figure 1 the section 12 of the shaft assembly 3 has an end face 35 inside the stuffing box 5, the end face 35 being the transition between the larger and smaller diameter sections of the shaft. The end face 35 is substantially perpendicular to the shaft axis.

The axial compressive stress in the packing material 7 will cause the material to press against the end face 35 of the section 12 of the shaft assembly 3. This allows for a substantial portion of the sealing effect of the packing seal to be exerted by the axial stress in the material. As the axial stress is directly set up by the gland follower 17 compressing the material it is substantially larger than the radial stress in the material. This greatly improves the efficiency of the seal against the shaft surface. Alternative embodiments of the seal are shown in Figures 2 to 8. Figures 2 to 4 show different configurations of the larger diameter section of the shaft assembly and its relation to the stuffing box and the opening in the end thereof. The remainder of the seal is substantially as shown and described in Figure 1.

With reference to Figure 2 the shaft assembly 40 comprises a shaft only, there being no outer sleeve. The section of larger diameter is in the form of a flange 41 formed directly on the shaft.

With reference to Figure 3 the shaft assembly 44 is shown wherein the diameter of the larger diameter section 45 is close to the inside diameter of the packing space 46. Effectively the stuffing box 47 has no end face, the packing space maintaining its diameter right through. This configuration exposes the largest possible amount of perpendicular face 48 on the shaft assembly 44, and has greatest sealing efficiency. With reference to Figure 4 the shaft assembly is shown having an alternative sleev configuration to that shown in Figure 1. Otherwise the two embodiments are substantially the same.

It will be readily appreciated that the embodiments of Figures 1 , 2 and 4 might be easily retrofitted into existing installations. In many situations these embodiments will require no modification to the gland housing or follower, needing only a cut down sleeve, replaced sleeve or welded flange on the shaft assembly.

Referring now to Figure 5, the figure depicts a double seal configuration in which a pair of stuffing box housings 50 and 51 are used to impart dynamic seal surfaces 52, 53 on each side of a flange 54. The flange 54 is carried on a sleeve 55 in the drawing, however this is clearly not a necessary feature and the flange 54 may extend directly from the shaft as earlier described. Dynamic sealing surfaces are also imparted between the packing material 56 and the axial surface 57 of the sleeve 55. The packaging box housings 50 and 51 are retained within gland housing 58, and are provided with a static seal comprising O-rings 59 in channels 60. The housings 50 and 51 are provided with means to draw in together to thereby compress the packing 56, the means being for example threaded shaft 61 drawn by nuts 62 extending through passages in the stuffing box housings.

In this form of the invention the flange 54 of the sleeve 55 is preferably of substantial length, so that each of the stuffing box housings 50 and 51 may overlap their ends 63 and 64 thereof respectively with the flange 54. It is readily apparent that drawing together the stuffing box housings 50 and 51 to compress the packing 56 will tend to equalise the packing pressure within the stuffing cavities, there being for example no particular restraint on the stuffing box housings 50 and 51 within the gland housing 58, while the shaft will generally be annularly fixed. The sleeve 55 is of course secured to the shaft, for example by keying and appropriately sealed in a static manner, for example by O-rings thereto.

The embodiment of Figure 5 provides the advantages of a double seal between the pressure end, say end 65, and the non-pressure end, say 66, with significant flexibility in positioning of flange 54, housings and means of adjustment.

With reference to Figure 6, a further alternative embodiment is shown having general similarity to Figure 3. In Figure 6 shaft 71 passes through a gland housing 70. The shaft 71 is fitted at the pressure end, with particular reference to examples concerning pumps and the like, say an impeller 72, shown only in part. Various bushes and thrust bearings may be provided, for example, neck bush 74. The shaft 71 is provided with a sleeve 76 which is keyed thereto or otherwise secured against relative rotational movement, and has a static seal therewith such as O-rings 77. The sleeve 76 includes outwardly extending flange 77 thereon, which in the form shown is fitted with a hardened vertical sealing face 78. End 79 of the sleeve 76 may be supported within a bush 75, however this is not crucial to the invention. At the low pressure end of the gland housing 70, the packing space defined by housing 70 and the axial and perpendicular sealing faces of the sleeve 76 is further enclosed by gland follower 73 which may be adjustably moved into that cavity to reduce the volume thereof and thus alter the pressure of the packing. The packing may comprise two or more annular rings 80 of packing material separated by a hard spacer 81. The hard spacer 81 improves the stress distribution within the packing, as large volumes of uninterrupted packing tend to develop non-homogeneous characteristics. The packing material 80 may for example comprise a graphite material of soft, low density physical form such as a graphite foil/fibre mixture.

With reference to Figure 7 where the sleeve 76 is shown, the sleeve may be configured to improve heat transfer by some degree of flushing with the sealing medium. A cavity 86 is provided between the sleeve 76 and the shaft 71, and a plurality of channels, each formed by a perpendicular or radial channel 83 and an axial channel 84 are provided into the cavity 86 adjacent the pressure end of the sleeve. These channels may for example be in relatively easy liquid communication with the high pressure area adjacent the impeller 72. The end 79 of the sleeve 76 is still supported on the shaft 71 by services 82 of the remaining sections 85 of the sleeve 76 at that end. These remaining sections 85 form a castellated appearance on that end of the sleeve. By this means liquid is able to communicate into the cavity 86, and thereby assist cooling, however the cavity is sealed effectively by static seals such as O-rings 77 adjacent its low pressure end.

The sleeve 76 is preferably provided from a material having a high hardness and high heat conductivity. It has been found that the pressures generated in the packing material by the gland follower 73 tend to allow the seal surfaces to run in a dry configuration, with very little seepage past the dynamic sealing surfaces, and that with packing materials such as the graphite material, and with sleeves of sufficiently high hardness, particularly the hardened face 78, exceptional seal life spans can be achieved.

With reference to Figure 8, a further variation is shown having a general configuration similar to that of Figure 6. In Figure 8 a shaft 91 passes through a gland housing 90. The shaft 91 is fitted for example with impeller 92 within a high pressure cavity 93. A sleeve 95 is fitted to the shaft 91, in a non-rotational manner and statically sealed thereto around each end 96 and 97 thereof. A gland follower 94 compresses packing 98 again with a spacer 99 in similar substance to that of Figure 6 within the packing space. A carbon bush 100 with metal sleeve is also depicted.

Figure 8 primarily depicts an alternative cooling system in which liquid is flushed between a flush inlet 101 and high pressure cavity 93, through cavity 102 between the sleeve 95 and the shaft 91. A plurality of inlet passages 103 are provided between the manifold 105 of flush inlet 101 and the cavity 102, and a plurality of outlet passages lead from the cavity 102. The outlet passages 104 preferably communicate between the high pressure cavity 93 and the end of the cooling cavity 102 adjacent the high pressure cavity 93 while the inlet passages 103 communicate between the manifold 105 of inlet 101 and cavity 102 adjacent the end thereof away from the high pressure cavity 93. In this manner a continuous flushing of liquid through the cavity 102 can be provided in either direction. For example it may be provided by introduction of a high pressure supply to the inlet 101 to flush toward the high pressure cavity 93, or it may be provided by bleeding and small and controlled amount of the medium being sealed against from the high pressure cavity 93.

With the configuration in Figure 8 enhanced cooling of the sleeve 95 can be achieved, alleviating some of the difficulties associated with the present invention, notably the high heat output induced by the more efficient application of pressure between the sealing surfaces of the packing 98 and the sleeve 95, particularly in the perpendicular sealing face 106.

Claims

CLAIMS:

1. A dynamic seal comprising: gland means, a shaft means passing through said gland means and having an annular face thereon extending substantially perpendicularly from the axial surface of said shaft means, an annular stuffing cavity defined by said gland means, said perpendicularly extending annular shaft means face and said axial shaft means surface, the volume of said cavity adjustable by stuffing cavity adjustment means, and packing in said stuffing cavity, such that when under compression from said stuffing cavity adjustment means, dynamic seal faces are induced at the interface between said packing and said shaft means axial surface and at the interface of said packing and said perpendicularly extending face.

2. A dynamic seal as claimed in claim 1 wherein said gland means comprises a gland housing and a gland follower, the position of said gland follower adjustable relative to said gland housing, said annular stuffing cavity defined by said gland follower, said gland housing, said perpendicularly extending annular shaft means face and said axial shaft means surface, the volume of said cavity adjustable by movement of said gland follower.

3. A dynamic seal as claimed in either claim 1 or claim 2 wherein said shaft means includes a sleeve fitted over a shaft, said sleeve incorporating said perpendicularly extending annular face and said proportion of said axial shaft surface which surrounds said annular stuffing cavity, said sleeve being secured against rotation relative to said shaft.

4. A dynamic seal as claimed in claim 3 wherein an annular cavity exists between said sleeve and said shaft, said sleeve is sealed around the circumference of said shaft at one end of said cavity, and said sleeve includes passageways into said annular cavity from the other end of said sleeve.

5. A dynamic seal as claimed in claim 4 wherein said passageways into said cavity comprise a plurality of passageways extending in said sleeve from an opening outside said cavity and adjacent the non-sealed end of said sleeve to an opening inside said cavity an adjacent the sealed end of said sleeve, and a plurality of passages extending from an opening adjacent the non-sealed end of said sleeve outside said cavity and an opening adjacent the non-sealed end of said sleeve inside said cavity, there being means to supply or receive liquid from one or other or both of said outside ends of said passages such that in use a liquid may pass through said cavity and aid in cooling said sleeve.

6. A dynamic seal as claimed in any one of claims 1 to 5 wherein said packing includes two or more annular rings of packing material separated by a hard annular spacer.

7. A dynamic seal as claimed in claim 6 wherein said packing material comprises graphite in a low density and soft physical configuration.

8. A dynamic seal as claimed in any one of claims 3 to 5 wherein said sleeve is formed from a hard heat conductive metal chemically compatible with the medium the ends whose passage the seal is acting.

9. A dynamic seal as claimed in claim 1 wherein said shaft means includes a second perpendicularly extending annular face thereon back to back with the first said annular face, and said gland means and said shaft means together define a second said annular stuffing cavity defined by said gland means, said second perpendicularly extending annular shaft means face and said axial shaft means surface, the volume of said second stuffing cavity adjustable by second stuffing cavity adjustment means.

10. A dynamic seal as claimed in claim 9 wherein said gland means includes a pair of stuffing box housings disposed on either side of a flange formed on said shaft by said first and second annular perpendicularly extending faces, each said stuffing box housing defining a said stuffing cavity together with a said perpendicularly extending annular face of said shaft and said axial shaft surface, and said first stuffing cavity adjustment means and said second stuffing cavity adjustment means comprising means whereby said pair of stuffing box housings may be drawn together, to compress said stuffing boxes with pressures therein attempting to equalise.

11. A dynamic seal as claimed in either claim 9 or claim 10 wherein said shaft means includes a sleeve fitted over a shaft, said sleeve incorporating a substantially perpendicularly extending flange having a said perpendicularly extending face on either side thereof, said sleeve being secured against rotation relative to said shaft.

12. A dynamic seal substantially as herein described with reference to and as illustrated by Figure 1.

13. A dynamic seal substantially as herein described with reference to and as illustrated by Figure 2.

14. A dynamic seal substantially as herein described with reference to and as illustrated by Figure 3.

15. A dynamic seal substantially as herein described with reference to and as illustrated by Figure 4.

16. A dynamic seal substantially as herein described with reference to and as illustrated by Figure 5.

17. A dynamic seal substantially as herein described with reference to and as illustrated by Figure 6.

18. A dynamic seal substantially as herein described with reference to and as illustrated by Figure 7.

19. A dynamic seal substantially as herein described with reference to and as illustrated by Figure 8.