AU6647381A - High pressure seal - Google Patents

Description

HIGH PRESSURE SEAL Technical Field

This invention relates to a rotary mechanical face seal of the type used to provide a seal between two members when one is moving in rotation relative to the other, for example a seal between the stationary wall of a housing of a pump or engine and a shaft extending through the wall. Such mechanical seals are used to prevent leakage of fluid between the shaft and the housing while permitting rotation of the shaft. Background Art

The invention is herein described with emphasis on a mechanical seal for use to prevent leakage of a fluid under a pressure higher than atmospheric pressure from a housing containing the fluid to atmospheric pressure outside the housing. The term "upstream" is herein used to mean a pressure on the high pressure side of a leakage path or potential leakage path of the fluid. Unless the context otherwise requires references to fluid pressure herein refer to the difference between the pressure inside and outside the housing and assume atmospheric pressure outside the housing and a higher than atmospheric pressure in the fluid. It will however be understood that in other embodiments of the invention apparatus generally similar to that to be described may be used when pressure outside the housing is higher than that inside the housing.

In a conventional type of rotary mechanical seal there is provided a tubular passage through which a shaft extends coaxially, a stationary seal seat mounted to and providing a seal with the passage, a drive ring mounted for rotation with the shaft and a ring element surrounding the shaft between the seat and the drive ring. The ring element is typically extended in the axial direction and has a ring face which is urged against the stationary seat face by springs acting between the drive ring and the ring element with a force sufficient to prevent leakage across a primary seal interface between the rotating ring face of the ring element and of the seat face of the stationary seal seat.

Such seals suffer from the disadvantage that the ring element may easily become misaligned with the shaft resulting in the face of the stationary seal seat and the face of the ring element intended to bear there against becoming misaligned. Misalignment of the faces results in excessive wear, tendancy to leak, and fretting of the shaft.

In order to alleviate those problems seals have been employed in which the ring element defines an annular recess between it and the shaft upstream from

OMPI /, WIPO the primary interface. The drive ring extends into the annular recess and provides a surface which permits limited sliding movement of the ring element with respect thereto in the axial direction while substantially maintaining the alignment of the ring element. An 0-ring seal grooved in the drive ring forms a secondary seal between the ring element and the drive ring and an O-ring between the drive ring and the shaft prevents leakage along the shaft surface.

In such seals the forces acting on the ring element to produce a reactive force at the primary interface act on an area of the ring element which is smaller than the area of the primary interface. Spring pressure between the drive ring and the ring element is required to ensure adequate sealing at the primary interface. As the fluid pressure which the seal is intended to withstand increases stronger and more elaborate spring means are required to maintain a seal at the primary interface. Consequently a range of seal designs has been required to cater for various applications. It has hereto been believed that to achieve a hydraulic loading of the ring element sufficient for provision of adequate sealing abutment of the ring face against the stationary seat at the primary interface would require a reduction in the area of the primary interface by an amount greater than the cross section of the annular recess upstream thereof, consequently shortening the leakage path across the primary interface, which has been considered undesirable, or by stepping the shaft diameter which is generally inconvenient or otherwise undesirable.

Moreover hydraulically loaded seals tend to sieze at the interface when very high pressures exist upstream of the interface unless special precautions are taken. Such seals when intended for use at pressure above 500 psi are costly and those for use at 1000 psi or 2000 psi are very costly.

In practice therefore rotating mechanical seals which rely substantially on hydraulic pressure acting on the ring element to provide sufficient abutment thereof with the seal seat to provide an effective seal at the primary interface have been avoided, especially when the seal is intended to withstand very high hydraulic pressures. Disclosure of Invention

The present invention stems from the suprising discovery that a very light hydraulic loading urging the ring element against the stationary seal seat will suffice to maintain a seal at fluid pressures upstream of the primary interface of up to in excess of 2000 psi and without seizure if the seal member is damped against movement away from the seal face.

Preferred embodiments of the invention provide a seal which is substantially self-aligning, which withstands high pressures, which is effective over a wide range of pressures and which is relatively inexpensive to manufacture and install in comparison especially with previously available high pressure rotary seals.

According to a first aspect the invention consists in a mechanical seal apparatus for providing a seal between two members when one member is rotating relative to the other said apparatus comprising: a seal seat fixedly mounted to and sealed with one of said members, said seal seat having a seat face, a ring element having a ring face adapted in the operating position of the ring element to bear against said seat face to provide a primary seal at the interface therebetween, said ring element being mounted to the other of said members by means permitting tanslational movement of said ring face towards or away from said seat face while maintaining a seal between the ring element and said other member; and wherein said ring element in order to move away from its operating position must displace a non-compressible fluid from a sealed chamber having a restricted aperture means permitting inlet and outlet of said fluid from said chamber.

According to a second aspect the invention consists in apparatus according to the first aspect wherein said chamber is in communication with a location at the ring element ring face which is between the upstream (as herein defined) and the downstream (as herein defined) edge of the primary interface. Brief Description of Drawings

The invention will now be described by way of example only with reference to the accompanying drawings in which:

Figures 1 to 2 and 4 to 6 are schematic diagrams showing a portion of various embodiments, each different from the other, of a seal assembly in diametric section.

Figure 3 shows a part of the embodiment of Figure 2, viewed in the axial direction.

Figure 7 shows a preferred embodiment of the invention in section.

Figure 8 shows a part end view of a ring element being a part of the embodiment shown in Figure 7. Best mode of carrying out the Invention

With reference to Figure 1 there is shown, by way of example only, schematically a first embodiment according to the invention.

The embodiment is a mechanical seal permitting rotation of shaft 1 with within a housing 2 in which oil at a pressure P greater than atmospheric pressure A is maintained. Shaft 1 extends to outside housing 2 which is at atmospheric pressure A.

The seal comprises an annular seal seat member 21 having a seat face 22 and sealed by means (not shown) with housing 2.

The seal further comprises a ring element 3 and a drive ring 4. Drive ring 4 is mounted to shaft 1 and comprises a generally cylindrical member sleeved oh shaft 1 and having an annular space defined between an inner cylindrical collar 40 adjacent to shaft 1 and an outer cylindrical collar 42 spaced radially apart therefrom.

The annular space is thus between a first cylindrical surface 41 on the radially outer side of inner collar 40 and a second cylindrical surface 43 on the inner side of outer cylindrical collar 42.

The annular space of drive ring 4 so defined is closed at one end by a wall 44 of drive ring 4 and is open at an end 45 which faces seat face 22.

Ring element 3 is interposed between seat face 22 and drive ring 4 and surrounds shaft 1. Ring element 3 has a ring face 31 which in the working position of ring element 3 is in abutment with seat face 22 at a common interface which is the primary seal interface. The opposite end of seal ring element 3 is annular, having an outer annular surface 32 and an inner annular surface 33 and is housed within the annular space defined between walls 41 and 43 of drive ring 4.

Drive ring 4 is mounted to shaft 1 by suitable means, for example, by threaded engagement therewith. First seal means being an "O" ring 51, grooved in drive ring 4 at its innermost circumference, provide a seal between drive ring 4 and shaft 1 preventing leakage of fluid under a pressure P greater than atmospheric pressure A upstream from seal along the shaft outer circumference towards the outer circumference towards the atmospheric pressure.

A second seal means being an "O" ring 52 is grooved in first cylindrical surface 41 of inner cylindrical collar 40 of drive ring 4 and extends between collar 41 and the outer annular surface 33 of ring element 3. A third seal means being an "O" ring 53 grooved in drive ring 4 extends between second cylindrical collar 42 of drive ring 4 from the second cylindrical surface 43 to outer surface 32 of ring element 3.

At the end of ring element 3 opposite ring face 31 there is a face 34 which together with surface 44 of drive ring 4, a portion of drive ring cylindrical surfaces 41 and 43 and "O" rings 52 and 53 defines a substantially sealed chamber.

A narrow passageway 8, or preferably a plurality of passageways provides an inlet and outlet communicating between the interior of the sealed chamber and are under pressure P surrounding the drive ring 4 when the apparatus is in use.

Pin means 11 having one end received in a blind hole in drive ring 4 and having the other pin and received in a blind hole of ring element 3 are adapted to drive ring element 3 in rotation with shaft 1 while permitting axial movement of ring element 3. "O" rings 52 and 53 also permit limited movement in the axial direction of ring element 3.

In use the sealed chamber becomes filled with oil under pressure and urges the ring element into engagement with the stationary seal seat at a primary seal interface of surface 22 and surface 31.

It is believed that any tendancy of the ring element to move away from the seat face requires displacement of fluid from the sealed chamber through narrow passageway 8 and is resisted by the fluid in the sealed chamber. Forces acting to maintain the ring element 3 in abutment with the seat increase as the pressure in the fluid increases, that is to say as the pressure against which the seal is effective increases. In practice the area of surface 34 may be small in comparison with that of the primary seal interface.

Since there is no, or only a small, nett component of force acting to urge the ring element into abutment with the seal face when fluid upstream of the primary interface is the same as or similar to the pressure downstream thereof, springs 13 may be interposed between drive ring 4 and ring element 3.

However the apparatus does not rely on those springs to maintain a primary seal at above a low pressure.

With reference to Figures 2 to 6 there is shown a second embodiment of a seal according to the invention. Numerals used to identify parts in Figure 1 are used to identify parts of corresponding function in Figures 2 to 9.

The embodiment of Figure 2 is similar to that shown in Figure 1 but differs in that passageways 8 extend in an axial direction through ring element 3 and communicate with a location on ring face 31 of ring element 3 between the outer radial and inner radial circumference thereof of ring face 3.

For preference a groove 35 more clearly visable in Figure 3 is recessed in the ring face 31 at a radius intermediate the inner and outer radial edge thereof. One or more passageways 8 (of which four are shown in Figure 3) communicate between groove 35 and the chamber defined between walls 34 and 44 (Figure 2) .

With reference to Figure 4 there is shown an embodiment in which a fourth "O" ring 54 grooved in drive ring 4 extends between ring element inner surface 33 and drive ring surface 41 intermediate ring face 31 and "0" ring 52.

Ring element 3 is stepped diameter on its internal surface having a greater diameter at the ring face 33 than at the opposite end 34. The step indicated at 36 occurs between seals 52 and 54. Drive ring 3 is stepped on surface 41 in the opposite sence as indicated at 46. In the present embodiment a sealed chamber is defined between surfaces 33 and surface 41 between seals 54 and 52 and including stepped surfaces 36 and 46.

Communication between the chamber so defined and fluid at pressure P surrounding ring element 3 is by at least one passage means 8 extending in a radial direction through ring element 3. - li ¬ lt should be noted that in this embodiment the chamber defined between surfaces 34 and 44 is not a sealed chamber containing a fluid and may communicate with atmosphere for example via a passageway (not shown) on shaft 1. The force acting on the ring element 3 with a component tendency to urge it towards seat face 21 in the embodiment of Figure 4, acts on a very small annular area of drive ring 3 at step 36.

For any differential in pressure of fluid between inside and outside housing 2 there is always a force acting on ring element 3 urging ring face 31 against seat face 21. The force increases as the differential in pressure increases but is sufficiently light to prevent seizure at the interface at very high pressure.

In the embodiment of Figure 5, drive ring 4 defines an annular space between inner cylindrical surface 43 of outer collar 42 and shaft 1.

A thrust element 9 which is also of generally annular shape is housed within the annular space between shaft 1 and cylindrical surface 43.

End wall 44 has_^equiangularly spaced blind holes 14 drilled therein to receive springs 91 which bear against flange 93 of the thrust element and urge it into abutment with ring element 3 at wall 34, in turn urging ring face 31 against seat face 21.

Thrust element 9 does not seal with shaft 1. However the outer annular surface 92 of thrust element 9 acts similarly to surface 41 of the embodiment of Figure 4. It is similarly stepped between "O" ring seals 54 and 52 with ring element 3. In the embodiment of Figure 5 a sealed chamber is provided between seals 54 and 52 the stepped outer surface 92 of thrust element 9 and a stepped inner surface 33 of ring element 3 communication with fluid at pressure P is via grooves 8 for preference communicating with ring face 31.

. Figures 7 and 8 show in more detail a preferred embodiment and the same numerals are used to describe the embodiment as are used to describe similar parts of earlier embodiments.

In the embodiment of Figures 7 and 8 the chamber defined between surfaces 33, 92 and "0" rings 52, 54 communicates with ring face 3 by two passageways 8. The passageways intercommunicate at the ring face by a coaxial groove 35 as also shown in the embodiment described with reference to Figure 3.

Figures 7 and 8 also show drive pins 11 which extends from a recess in drive ring 4 through flange 93 of thrust element 9 and into a cavity of ring element 3.

Three drive pins 11 are provided at equiangular spacing.

Intermediate the drive pins and at equiangular spacing are springs 13 received in blind holes 14 of drive ring 4, the springs bearing at one end against the flange of thrust element 9.

Springs 13 maintain ring face 31 in contact with seat face 22 when fluid in the apparatus is substantially not under pressure.

Apparently fluid bending to escape aacross the primary seal interface enters the sealed chamber via passageway 8 under pressure.

When fluid within housing 2 is under pressure thrust element 9 moves away from seat element 21. However its movement is limited by abutment thereof against the drive ring 4. Ring element 3 is urged by fluid pressure within the chamber towards the primary interface and leakage is thereafter prevented.

Figure 6 illustrates an embodiment in which a sealed chamber is provided between drive ring face 44, seal 53 and face 34 of ring element 3. In this case inlet and outlet of fluid to the chamber is at an annular gap at the periphery of the chamber. A passage thru shaft 1 communicates with the space defined between seals 52, 51 and 53 and has no significant effect on the normal working of the seal.

Figure 9 illustrates an embodiment in which the ring element has a collar which sleeves the drive ring and in which the sealed chamber is defined between shaft 1 drive ring wall 44, ring element wall 34 and seal 53.

It will be understood that in practice, embodiments shown in Figures 1 to 6 also require means for driving the ring element with the drive ring such as for example pins 11 of Figure 7 and require springs to prevent leakage when the fluid in the sealed chamber is not under pressure such springs 13 of Figure 7. It will further be understood that drive ring 4 may be mounted to shaft 1 by other means for example grub screws.

The seal interface preferably has a carbon seat member and a steel face ring.

Those skilled in the art will readily appreciate that the seal may be modified for situations in which a pressure within the housing is lower than that outside the housing and that the elements described herein as mounted to the rotating member may in other embodiments be exchanged with those mounted to the stationary member without departing from the invention herein described. Industrial Applicability

The invention has industrial application in pumps, motors, compressors and generally when leakage of fuild between a shaft and stationary parts.

Claims (17)

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:-

1. A mechanical seal apparatus for providing a seal between two members when one member is rotating relative to the other said apparatus comprising: a seal seat fixedly mounted to and sealed with one of said members, said seal seat having a seat face, a ring element having a ring face adapted in the operating position of the ring element to bear against said seat face to provide a primary seal at the interface therebetween, said ring element being mounted to the other of said members by means permitting translational movement of said ring fa.ce towards or away from said seat face while maintaining a seal between the ring element and said other member; and wherein said ring element in order to move away from its operating position must displace a non-compressible fluid from a sealed chamber having a restricted aperture means permitting inlet and outlet of said fluid from said chamber.

2. Apparatus according to claim 1 wherein said chamber is in communication with a location at the ring element ring face which is between the upstream (as herein defined) and the downstream (as herein defined) edges of the primary seal interface.

3. Apparatus according to claim 1 or claim 2 wherein said chamber is in communication with a groove recessed in said ring element ring face said groove extending in a direction coaxial with said ring face and lying between the upstream edge and the downstream edge of the primary seal interface.

4. Apparatus according to claim 1 wherein said aperture means is in communication with a fluid under pressure upstream from the upstream edge of the primary seal interface.

5. Apparatus according to any one of the preceding claims wherein said aperture means comprises a

' plurality of ducts of restricted cross section.

6. Apparatus according to any one of the preceding claims wherein the net area of the ring element against, which said non compressible fluid can exert a force having a component urging the ring element towards the seat face is small in comparison with the area of the primary seal interface.

7. Apparatus according to any one of the preceding claims further comprising resilient means for biasing the ring element in abutment with the seal seat if said non-compressible fluid is at the same pressure or is at a small pressure, greater than the pressure on the downstream side of said interface.

8. Apparatus according to any one of the preceding claims wherein one of said members is a rotating shaft and the other is a tubular passageway through which the shaft extends coaxially, said apparatus comprising a seal seat mounted to and providing a seal with said passage, a drive ring mounted for rotation by the shaft, a ring element surrounding the shaft between the seal seat and the drive ring and being driven in rotation by the drive ring by means permitting some movement of the ring element in the shaft axial direction, first seal means providing a seal between the drive ring and the shaft, and second seal means providing a seal between the drive ring and the ring element while permitting said movement in the shaft axial direction.

9. Apparatus according to claim 8 wherein said drive ring has a cylindrical collar which encircles a torroidal portion of the ring element.

10. Apparatus according to claim 8 or claim 9 wherein said second seal means extends between the inner radial face of the collar and the outer radial face of the torroidal portion of the ring element.

11. Apparatus according to claim 10 further comprising a chamber between a third seal means and a fourth seal means spaced apart in the axial direction from the third seal means, the third and fourth seal means each extending between an inner radial surface of the ring element and a surface encircled by said ring element inner radial surface, said surface encircled extending between said third and fourth seal means.

12. Apparatus according to any one of claims 8 to 10 further comprising a thrust element which is resiliently biased from the drive ring and which acts on the ring element to urge it towards the primary seal interface.

13. Apparatus according to claim 12 when dependant on claim 11 wherein an outer radial surface of the thrust element is a surface encircled by the ring element and extending between the third and fourth seal means.

14. Apparatus according to any one of claims 11 to 13 wherein said chamber is in communication with a fluid upstream from said primary seal interface by means of at least one narrow passageway extending through the ring element to an outer radial surface thereof.

15. Apparatus according to any one of claims 11 to 13 wherein said chamber is in communication with the ring element ring face by means of at least one narrow passageway extending through the ring element.

16. Apparatus according to claims 8, 9 or 10 wherein a third seal means extends between an inner radial surface of the ring^* element and said shaft, said third seal means permitting said axial movement, a chamber between said drive ring and said ring element, said chamber being in communication with fluid upstream from the primary seal interface at a narrow circumferential gap between the ring element and the drive ring.

17. Apparatus according to any one of claims 8 to 10 wherein said drive ring comprises a torroidal space defined between a first cylindrical surface and a second cylindrical surface spaced radially outwards from the first, said ring element has a torroidal portion partially housed within said torroidal space; second seal means extending between the outer torroidal surface of the ring element and said second cylindrical surface, and third seal means extending between the inner torroidal surface of the ring element and said first cylindrical surface; said drive ring, ring member and said second and third seals defining a sealed chamber, and passage means communicating between said sealed chamber and fluid upstream of the downstream primary seal interface edge.