AU620569B2 - A mechanical seal - Google Patents

Description

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INTERNATIONAL APPLI I UQU UsSH 5 U R e PATENT COOPERATION TREATY (PCT) (51) International Patent Classification 4 (11) International Publication Number: WO 89/ 02555 F16J 15/36 Al (43) International Publication Date: 23 March 1989 (23.03.89) (21) International Application Number: PCT/GB88/00726 (81) Designated States: AT, AT (European patent), AU, BB, BE (European patent), BG, BJ (OAPI patent), BR, (22) International Filing Date: 2 September 1988 (02.09.88) CF (OAPI patent), CG (OAPI patent), CH, CH (European patent), CM (OAPI patent), DE, DE (European patent), DK, FI, FR (European patent), GA (31) Priority Application Number: PI 4303 (OAPI patent), GB, GB (European patent), HU, IT (European patent), JP, KP, KR, LK, LU, LU (Euro- (32) Priority Date: 11 September 1987 (11.09.87) pean patent), MC, MG, ML (OAPI patent), MR (OA- PI patent), MW, NL, NL (European patent), NO, (33) Priority Country: AU RO, SD, SE, SE (European patent), SN (OAPI patent), SU, TD (OAPI patent), TG (OAPI patent), US.

(71) Applicant (for all designated States except US): FLEXI- BOX LIMITED [GB/GB]; Nash Road, Trafford Park, Published Manchester M17 ISS With international search report.

(72) Inventor; and Inventor/Applicant (for US only) KNIGHT, John, Anthony [AU/AU]; 10 Tulloch Court, Bacchus Marsh, 25 MAY 189 VIC 3340 P. 2 5 MAY 1989 (74) Agent: MASSEY, Alexander; Marks Clerk, Suite 301, Sunlight House, Quay Street, Manchester M3

AUSTRALIAN

3JY 17 APR 1989 PATENT OFFICE (54) Title: A MECHANICAL SEAL (57) Abstract A mechanical seal to seal a rotating shaft that extends from a housing which contains a product fluid to be retained within the housing comprises a first seal (11) element coupled to the shaft and a second seal element (13) coupled to the housing The mechanical seal is characterised by the provision of an elastomeric bellows (19) connected at one end to the second seal element (13) and at the other end to the housing the bellows (19) having a radially disposed surface responsive to the pressure of the product fluid, whereby the closing force acting on the second seal element (13) is a combination of the spring action of the bellows (19) and the pressure of the product fluid acting on the surface. As a result of this arrangement the bellow. (19) is responsive to changes in pressure in the product fluid to vary the area of the surface thereby to vary the closing force.

r 1989 PT/B I0 0726 113 9-1 A MECHANICAL SEAL The invention relates to a mechanical seal to seal a rotating shaft that extends through a stationary housing which contains a fluid product.

GB-A-1335642 discloses a mechanical seal for preventing leakage between a housing and a rotating shaft extending through and out of the housing of a liquid under pressure contained within the housing.

The mechanical seal comprises a first seal element coupled to the shaft for rotation therewith, and a second and non-rotatable seal element coupled to the housing, the seal elements being in face-to-face contact as is customary.

A flexible bellows bowed outwardly of the rotating shaft is clamped at one end between the housing a fixed annular support member, and has its other end sealed in a groove in an axially-movable, non-rotatable carrier member which supports the non-rotatable seal element.

The liquid under pressure within the housing acts on the outer shaft-remote surface of the outwardly bowed bellows to generate a wedging action tending to cause an axial extension of the bellows to urge the non-rotatable seal element against the rotating seal element to resist the aforesaid leakage. The closing force applied to the non-rotatable seal element is therefore a combination of the spring action of the bellows and the liquid pressure acting on the exterior of the bellows.

It is an-e jee t of the present invention to provide a mechanical seal of the same general character as that disclosed in GB-A-1335642 which has a bellows configuration Sallowing an improved and more efficient application of the pressure liquid component of the closing force.

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According to the present invention there is provided a mechanical seal to seal a rotating shaft that extends from a housing which contains a product fluid to be retained within the housing, comprising: a first seal element coupled to the shaft; a second seal element coupled to the housing; and an elastomeric annular bellows of substantially Ucross-section surrounding the shaft with one end thereof connected to the second seal element and the other end to the housing and with the closed end of the U-bellows adjacent to the shaft, the limb of the U-bellows adjacent and connected to the second seal element defining a radially-disposed annular surface constituting a second seal element loading area adapted to vary in response to variations in the pressure of the product fluid acting on the closed end of the U-bellows to vary the position of the closed end relative to theI shaft to increase or decrease the loading area thereby varying the seal element-to-seal element closing force, which is a 20 combination of the spring action of the bellows and the pressure of the product fluid.

The arrangement is such that at relatively low pressure the annular, radially-extending surface area responsive to the pressure of the product fluid is relatively low. As a consequence, the closing force is also relatively low. However, as the pressure of the product fluid increases the bellows expands radially inwardly to reduce the inner diameter of the bellows and increase the annular, radially-extending surface area thereof. The expansion of the bellows causes an increase in the surface area responsive to the pressure of the product fluid so that the closing force increases. The inner diometer of the bellows, the material from which the bellows is formed and the thickness are elected to allow a predetermined variation in inner diameter and surface area over a range of pressures of product fluid.

It is preferred that the mechanical seal further comprises an annular support sleeve radially inwards of the bellows to limit the inward expansion of the bellows.

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i 1 .1 In a preferred arrangement the first seal element is connected to a sleeve which is mounted by an annular collar onto the shaft. The second seal element is connected to one end of the bellows by mechanical means such as press fits, clamp rings or adhesives. The other end of the bellows is clamped to the housing thus allowing reaction torques to be transmitted from the second seal element to the housing and thereby effectively keeping the second seal element from rotating whilst still allowing second seal element to axially and angularly travel to accommodate normal wear, floats and runouts.

A detailed description of a preferred embodiment of the present invention is now provided with reference to the accompanying drawing in which:- Fig. 1 is a cross-section through a preferred embodiment of a mechanical seal in a closed position to seal a rotating shaft extending from a housing containing a product fluid; and Fig. 2 is a section showing the .effect of varying pressures on the U-shaped bellows shown in Fig. 1.

In Fig. 1 is shown a housing 3 which contains a volume of product fluid under pressure, a rotating shaft 7 extending from the housing 3 and a mechanical seal generally identified by the numeral 9 positioned to prevent the escape of the product fluid through the generally annular gap 10 between the shaft 7 and the housing 3.

The mechanical seal 9 comprises two seal elements 11 and 13 having respective annular faces 1 SU i. -oSUR~i~ i (U7h H3T 4 and 17. In the position shown in the figure the two annular faces 15 and 17 are in contact thereby to define the seal.

The seal element 11 is connected to and rotates with the shaft 7 by means of a sleeve 18 which is mounted to the shaft 7 by a collar 20. The collar 20 comprises two halves (not shown) which act to press the sleeve 18 onto the shaft 7 to provide the necessary drive. The sleeve 18 is split at its end for this reason.

The seal element 13 is supported by an elastomeric bellows 19 which is generally U-shaped in longitudinal half-section. The seal element 13 is positively fixed to the bellows at 21 so that a static seal is arranged at the interface and also so that frictional torque on seal element 13 effectively is transferred to the bellows 19.

In the preferred arrangement a metallic support ring 20 is moulded to the bellows 19 so that the bellows 19 is circumferentially supported to allow radial compression of the elastomeric material between the support ring 20 and the seal element 13 thereby to effect a leak free joint.

It is also envisaged that the leak free joint could be.

effected by the use of separate clamp rings or adhesive bonding.

The mechanical seal bellows 19 also comprises a flanged section 22 which allows the bellows 19 to be positively clamped to the housing 3 by a clamp ring 23 pulled into correct position by set screws 24.

Thus, the seal element 13 (hereinafter referred to as the stationary seal element), is elastically fixed to the housing 3 and elastically urged against the seal element 11 i (hereinafter referred to as the rotary seal element) by preloading the bellows 19 by bending the elastomer into the U-shaped configuration.

0*,42 IN 0 r T The seal elements may be formed from any suitable materials selected in accordance with a number of parameters which include the speed of rotation of the shaft 7 and the nature of the product fluid 5. Suitable materials for the rotary and stationary seal elements 11 and 13 include sintered ceramics, alloy metals and carbon.

Suitable materials for the bellows 19 include any natural and synthetic rubbers and other elastomeric materials such as polyurethane and these may if required be reinforced by fibrous or woven material.

Referring now to Fig. 2, the mechanical seal further comprises a support sleeve 25 which has its outside diameter selected to clear by a predetermined spacing the inside of the bellows at 26. The support sleeve 25 defines a limit stop for the bellows 19, as will be described hereinafter.

In use, as the bellows 19 is pressured by product fluid 5 within the housing 3 it will elastically deform and expand radially inwardly towards the support 25. At zero pressure there will be no inwards stretching effect but as the pressure of the product fluid 5 increases the bellows 19 will reduce in diameter at 26 effectively increasing its radially disposed area. As a consequence, the closing force acting against the stationary element 13 increases.

Thus, it is possible, to select the closing forces per unit pressure of product fluid by reference to the nature of the' elastomeric material and the thickness of the bellows 19.

As a consequence, the seal can be arranged for very low initial hydraulic closing forces without the risk of overbalancingr occurring at higher pressures.

Claims (6)

1. A mechanical seal to seal a rotating shaft that extends from a housing which contains a product fluid to be retained within the housing, comprising: a first seal element coupled to the shaft; a second seal element coupled to the housing; and an elastomeric annular bellows of substantially U- cross-section surrounding the shaft with one end thereof connected to the second seal element and the other end to the housing and with the closed end of the U-bellows adjacent to the shaft, the limb of the U-bellows adjacent and connected to the second seal element defining a radially-disposed annular surface constituting a second seal element loading area adapted to vary in response to variations in the pressure of the product fluid acting on the closed end of the U-bellows to vary the position of the closed end relative to the shaft to increase or decrease the loading area thereby varying the seal *o element-to-seal element closing force, which is a 20 combination of the spring action of the bellows and the pressure of the product fluid.

2. A mechanical seal as claimed in claim 1 comprising a stationary annular support sleeve disposed radially inwardly of the bellows to limit radial inward expansion 25 of the bellows under the pressure action of the product fluid.

3. A mechanical seal as claimed in claim 2, in which the .support sleeve is integral with the housing.

4. A mechanical seal as claimed in any one of claims 1 to 3, in which the first seal element is connected to a sleeve which is mounted by an annular collar onto the shaft, the second seal element is connected to one end of the bellows by mechanical means and the other end of the bellows is clamped to the housing thus allowing reaction I RA 4 q.5 torques to be transmitted from the second seal element to fR r; -i 7 the housing and thereby effectively keeping the second seal element from rotating whilst still allowing the second seal element to axially and angularly travel to accommodate normal wear, floats and runouts.

5. A mechanical seal as claimed in claim 4, in which the mechanical means connecting the second seal element to the bellows comprises a press fit therebetween, clamp ring means or adhesive.

6. A mechanical seal substantially as herein described with reference to the accompanying drawings. DATED this 3rd day of December 1991 FLEXIBOX LIMITED By their Patent Attorneys GRIFFITH HACK CO 0. 0 5 o@ 0 S

11420-F/426