WO1990008911A1

WO1990008911A1 - Shaft seal arrangement

Info

Publication number: WO1990008911A1
Application number: PCT/GB1990/000103
Authority: WO
Inventors: Neil Mcintosh Wallace; Jacobus Anton Martinus Ten Houte De Lange
Original assignee: Flexibox Ltd
Current assignee: Flexibox Ltd
Priority date: 1989-01-26
Filing date: 1990-01-25
Publication date: 1990-08-09
Anticipated expiration: 1991-07-26
Also published as: AU4959090A; GB8901656D0

Abstract

A shaft seal arrangement comprises a main mechanical seal (14) and a back-up mechanical seal (15) with a barrier fluid reservoir communicating with the latter. A pumping ring (21) surrounds and is rotatable with the rotating sealing ring (16) of the back-up mechanical seal (15) and is disposed relative to the latter so that the rotating and stationary sealing rings (16)(17) are subjected to a positive fluid pressure during use resulting in enhanced wearlife of the back-up mechanical seal (15).

Description

SHAFT SEAL ARRANGEMENT

This invention relates to a shaft seal arrangement.

Such an arrangement commonly comprises a mechanical seal comprising a rotatable seal element fast with a rotating shaft or shaft sleeve and in running or rubbing contact with a stationary seal element secured to a casing within which the shaft rotates.

It is common practice to provide a pumping ring to rotate with the rotating seal element and which cooperates with ducting surrounding the mechanical seal to circulate a barrier fluid around the seal elements and between the latter and a barrier fluid reservoir.

It is an object of the present invention to provide a shaft seal arrangement comprising a mechanical seal with an associated barrier fluid pumping ring which provides for an increased wearlife of the mechanical seal compared with existing shaft seal arrangements.

According to the present invention there is provided a shaft seal arrangement comprising a mechanical seal constituted by a rotatable seal element having an annular sealing face in running contact with an annular sealing face of a stationary seal element, and a pumping ring for controlling flow of a barrier fluid to the seal elements and disposed relative to the mechanical seal so that the latter is located on the discharge side of the pumping ring whereby the annular sealing faces are placed under positive barrier fluid pressure.

Also according to the present invention there is provided a shaft seal arrangement comprising, in tandem, main and back-up mechanical seals, each constituted by a rotatable seal element having an annular sealing face in running contact with an annular running face of a stationary seal element, and a pumping ring associated with the back-up mechanical seal for controlling flow of a barrier fluid to the back-up mechanical seal which is disposed on the discharge side of the pumping ring so that the annular sealing faces thereof are placed under positive barrier fluid pressure.

As a result of this positive pressure the wearlife of the mechanical seal Is substantially enhanced.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:-

Fig. 1 is a half-sectional longitudinal view of a shaft seal arrangement according to the present invention;

Fig. 2 is a similar view of a second shaft seal arrangement;

Fig. 3 is a fragmentary longitudinal sectional view of a third shaft seal arrangement; and

Fig. 4 is a fragmentary sectional view of a fourth shaft seal arrangement.

In Fig. 1_. there is shown a casing 10 traversed by a rotating shaft 11 in which is made fast, as indicated at 12, a shaft sleeve 13.

A pair of mechanical seals 14 and 15 (main and back-up seals) seal the product fluid in the casing 10 from the shaft 11 and shaft sleeve 13.

The back-up mechanical seal 15 comprises a rotating sealing ring 16 fast with the shaft sleeve 13 and a stationary sealing ring 17 secured at 18 to the casing 10 to prevent rotation but not axial movement of the sealing ring 17.

A barrier fluid, as is customary, is circulated from a reservoir (not shown) to the sealing rings 16 and 17 and back to the reservoir. The inlet and outlet for the barrier fluid in the casing 10 are indicated respectively at 19 and 20 and are closely-adjacent one to another in axial terms.

A surrounding pumping ring 21 is secured to the rotating sealing ring carrier portion 22 of the shaft sleeve 13, the pumping ring 21 having an outer circumference of scroll or screwthreaded configuration as indicated at 23. The pumping ring 21 and its associated flow path as hereinafter described is arranged relative to the back-up mechanical seal 15 so that the latter is disposed on the discharge side of the pumping ring 21, as a result of which the sealing rings 16 and 17 are placed under positive pressure with consquent increase in their" wearlife.

A ducting ring 24 is fixed to the casing 10 as indicated at 25 and comprises a wall portion 26 surrounding the pumping ring 21 in closely-adjacent, radially-spaced relationship.

The ducting ring 24 downstream of the pumping ring 21, in terms of barrier fluid flow, has a series of angularly-spaced holes 27 permitting flow of the barrier fluid of the interior of the ducting ring 24 and its exterior.

The barrier fluid inlet 19 communicates with an inlet passage 28 in the casing 10 defined, inter alia, by a wall 29 which stops short of the shaft sleeve 13 to provide an annular opening 30 through which barrier fluid can flow to the pumping ring 21 which is thus disposed radially outwards of the annular opening 30.

The flow of barrier fluid is indicated by arrows and is radially inward through inlet 19 and passage 28 to the shaft sleeve 13, through sleeve 13, through opening 30, radially outwards to the pumping ring 21, axially through the narrow annular passage between the pumping ring 21 and the ducting ring 24 (a screw pump arrangement), radially inwards into contact with sealing rings 16 and 17, radially outwards through the holes 27 and finally axially and radially outwards through an outlet passage 31 to the outlet 20.

In Fig. 2, parts identical to those of Fig. 1 are designated by the same references with the suffix "A".

In this embodiment, the pumping ring 32 has an annular slot 33 adjacent the rotating sealing ring carrier 22A and with which communicate a series of angularly-spaced radial holes 34.

The ducting ring 35 is fixed to the casing 10 A as indicated at 36 and comprises an axial wall 37 terminating adjacent the pumping ring 32 downstream, in terms of barrier fluid flow, of the holes 34 and is formed with a hole 38 aligned with the outlet passage 31A and outlet 20A for the barrier fluid.

The ducting ring 35 downstream of the hole 38 and radially inwards thereof is formed with a series of angularly-spaced holes 39.

The axial wall 37 of the ducting ring 35 is of multiple scallop configuration which defines a series of angularly-spaced, parallel, axial flow ducts.

In this embodiment, the barrier fluid flow is radially inwards through the inlet 19A and the inlet passage 28A, through opening 30A and radially outwards to the pumping ring passage 33, radially outwardly through holes 34 (centrifugal pumping action), axially through the scalloped insert ducts, radially inwards through holes 39 to contact sealing rings 16A, 17A axially and finally radially outwards through hole 38, outlet passage 31A and outlet 20A.

Referring now to Fig 3, the casing is indicated at 40 and has barrier fluid inlet and outlet passages 41 and 42.

The back-up mechanical seal comprises, as usual, a rotating sealing ring 43 in annular running contact with a stationary sealing ring 44.

The rotating sealing ring 43 is fast with a shaft sleeve 45 and is surrounded by a pumping ring 46 having an outer scroll or screwthread surface.

The pumping ring 46 is fast with an annular spring carrier 47 which rotates with the rotating sealing ring 43 and houses angularly spaced springs 48 serving to urge the rotating sealing ring 43 against the stationary sealing ring 44 as is usual.

An annular axial passage 49 is provided between the spring carrier 47 and the rotating sealing ring 43 for passage of barrier fluid into the spring carrier 47 from which it egresses through axial holes 50 to outlet passage 42.

This arrangement ensures that any vapour accumulating in the region of the sealing rings 43, 44 is entrained back by the flowing barrier fluid towards the reservoir via the outlet passage 42.

The total cross-sectional area of the holes 50 is selected to ensure that a positive pressure prevails at the sealing rings 43 and 44.

In Fig. 4, the casing is designated 50 and the barrier fluid inlet and outlet 51 and 52 respectively.

The rotating sealing ring is indicated at 53 and the stationary sealing ring is indicated at 54.

The stationary sealing ring 54 has connected thereto an anti- rotational annulus 55 with a scalloped annular insert defining axial ducts 56 between the stationary sealing ring 54 and the anti-rotational annulus 55.

These ducts 56 open to spring housings 57 in which are located springs 58 urging the annular running faces of the sealing rings 53 and 54 in contact.

A pumping ring 59 which may be an integral part of a shaft sleeve 60 surrounding a rotatable shaft 61, or a seperate component rotatable therewith is disposed between a barrier fluid inlet passage 62 opening from the barrier fluid inlet 51 to the shaft sleeve 60.

The pumping ring 59 is formed with a series of angularly-spaced radial holes 63 which communicate with the inlet passage 62 via an annular gap 64 at the shaft sleeve 60.

A ducting ring 65 surrounds the sealing rings 53 and 54 and defines therewith an annular axial passage 66 for the barrier fluid centrifugally egressing from the radial holes 64.

This passage 66 is in communication with the ducts 56 and/or with the radial holes 67 in the ducting ring 65 adjacent the anti- rotational annulus 55.

The radial holes 67 communicate with a barrier fluid outlet passage 68.

The spring housings 57 also communicate with the barrier fluid outlet passage via a radial/axial passage 69.

It is to be understood that both the ducts 56 and the radial holes 67 can be provided, or either of them, to provide communication between the axial passage 66 and the barrier fluid outlet passage 68.

A sealing ring 70 is provided between the pumping ring 59 and the ducting ring 65 to resist any return flow of the barrier fluid centifugally egressing from the radial holes 63 to the barrier fluid inlet passage 62.

With this shaft seal arrangement, the pumping ring 59 again has on its discharge side the sealing rings 53 and 54 which consquently, in use, are under positive fluid pressure giving an enhanced wearlife thereto.

While reference has been made to circulation of the barrier fluid it is to be clearly understood that the barrier fluid can be contained with a dead end chamber within the shaft seal arrangement, i.e. no circulation, and the action of the pumping ring will, in this instance, still place the annular sealing faces under positive barrier fluid pressure. It should also be noted that where the shaft seal arrangement contains only a single mechanical seal the fluid subjected to the action of the pumping ring, with or without circulation, is not a barrier fluid and the term "barrier fluid" used herein and in the claims should be construed accordingly.

Claims

1. A shaft seal arrangement comprising a mechanical seal constituted by a rotatable seal element having an annular sealing face in running contact with an annular sealing face of a stationary seal element, and a pumping ring for controlling flow of a barrier fluid to the seal elements and disposed relative to the mechanical seal so that the latter is located on the discharge side of the pumping ring whereby the annular sealing faces are placed under positive barrier fluid pressure.

2. A shaft seal arrangement comprising, in tandem, main and back¬ up mechanical seals, each constituted by a rotatable seal element having an annular sealing face in running contact with an annular sealing face of a stationary seal element, and a pumping ring associated with the back-up mechanical seal for controlling flow of a barrier fluid to the back-up mechanical seal which is disposed on the discharge side of the pumping ring so that the annular sealing faces thereof are placed under positive barrier fluid pressure.

3. A shaft seal arrangement as claimed in claim 1 or 2 in which the or each rotatable seal element is fast with a rotating shaft or shaft sleeve while the or each stationary seal element is secured to a casing within which the shaft rotates.

4. A shaft seal arrangement as claimed in claim 3 associated with a reservoir containing the barrier fluid, the reservoir being connected to a barrier fluid inlet passage and a barrier fluid outlet passage provided in the casing, and circulation of the barrier fluid between the reservoir and the mechanical seal being controlled by the pumping ring.

5. A shaft seal arrangement as claimed in any one of claims 1 to 4 in which the pumping ring surrounds and is rotatable with the rotating seal elelment.

6. A shaft seal arrangement as claimed in claim 4 or 5 in which the barrier fluid inlet passage extends radially inwardly of the pumping ring and opens, for passage of barrier fluid to the pumping ring, at, or immediately adjacent to, the rotating shaft or associated shaft^* sleeve.

7. A shaft seal arrangement as claimed in claim 6 in which a wall of the casing which constitutes part of the barrier fluid inlet passage stops short of the shaft or shaft sleeve whereby the barrier fluid is constrained to pass radially inwardly to the rotating shaft or shaft sleeve and then to reverse direction (radially outwardly) to reach the pumping ring.

8. A shaft seal arrangement as claimed in claim 7 in which the barrier fluid inlet and outlet passages are disposed in closely- adjacent, axially-spaced relationship.

9. A shaft seal arrangement as claimed in any one of claims 4 to 8 comprising a ducting ring axially spaced from the pumping ring and defining therewith a passage for controlled flow of the barrier fluid from the inlet passage around the seal elements to the outlet passage.

10. A shaft seal arrangement as claimed in claim 9 in which the pumping ring has a scroll or screwthread outer circumference closely adjacent to an axial wall of the ducting ring which has a plurality of angularly-spaced holes downstream of the pumping ring, in terms of barrier fluid flow, through which the barrier fluid flows to its outlet passage.

11. A shaft seal arrangement as claimed in claim 9, in which the pumping ring, has a plurality of radial holes through which barrier fluid is centrifugally diverted to flow through parallel ducts defined by an annular scallop-shaped insert disposed between a wall of the ducting ring and the barrier fluid outlet passage, the barrier fluid thereafter flowing to its outlet passage via a hole in the insert between adjacent ducts.

12. A shaft seal arrangement as claimed in any one of claims 1. to 5 in which the barrier fluid inlet passage opens to the pumping ring radially outwards of the latter, an axial passage being provided between the pumping ring and the rotating seal element for return flow of the barrier fluid to its outlet passage.

13. A shaft seal arrangement as claimed in claim 12 in which the axial passage opens to the outlet passage through at least one axial hole in a spring carrier associated with the rotating seal element.

14. A shaft seal arrangement as claimed in any one of claims 1 to 4 in which the pumping ring has a plurality of radial holes through which barrier fluid centrifugally egresses into an axial annular passage defined by a ducting ring surrounding the sealing elements from which the barrier fluid egresses to the barrier fluid outlet passage through radial holes in the ducting ring and/or axial ducts between the stationary sealing element and an associated anti- rotational annulus.

15. A shaft seal arrangement as claimed in claim 14, in which the axial ducts communicate with the barrier fluid outlet passage via the spring housings and a communicating annular passage between the latter and the barrier fluid outlet passage.

16. A shaft seal arrangement as claimed in claim 14 or 15 in which the pumping ring is an intergral part of the shaft sleeve, or is a seperate component rotatable therewith.

17. A shaft seal arrangement as claimed in any one of claims 14 to 16 comprising a sealing ring between the pumping ring and the ducting ring to resist any reverse flow of the barrier fluid back to its inlet passage.