GB2255379A - Back-up shaft seals - Google Patents

Abstract

A shaft seal in which a rotary seal member 13 fast with a rotatable shaft 19 is in face to face rubbing contact with a stationary seal member 12 fast with a stationary housing 10 surrounding the rotatable shaft. The stationary seal member is supported by a radially-extending flexible annular diaphragm 22 the outer edge of which is clamped to the housing. An annular support plate 24 is mounted on the housing adjacent a low pressure side of the diaphragm so that when a pressure differential appears across the seal the diaphragm is displaced towards the annular support plate. The support plate extends radially inwards from the clamped peripheral edge of the annular diaphragm to adjacent the stationary seal member. The diaphragm is arranged so that, in the initial assembled condition of the shaft seal, it is inclined out of face to face contact with the annular support plate except at its clamped peripheral edge. <IMAGE>

Description

BACK-UP SHAFT SEALS This invention relates to shaft seals and in particular back-up shaft seals.

A common form of shaft seal well-known to those skilled in the art is a mechanical seal comprising a rotary seal member fast with a rotatable shaft and a stationary seal member fast with a stationary housing surrounding the rotatable shaft, the seal members being in face-to-face rubbing contact, and means, for example mechanical springs or bellows, being provided to apply contacting pressure to the seal members and to take up or compensate for wear occurring during use. Such mechanical springs or bellows are secured against rotation and are axially disposed between the stationary housing and the stationary seal member of the mechanical seal.

The fitment of such an axially-extending mechanical springs or bellows complicates the manufacture of mechanical seals and their presence imposes a restriction on the overall length of mechanical seals i.e. imposes a greater axial length cn the mechanical seal than is often desirable.

In our PZT application No. GB90!00527 (publication No. 1 fO90il2230) we proposed a simpler pressure-applying means for the stationary seal member of a mechanical seal with the added advantage cf permitting a reduction in the overall axial length of the mechanical seal.

This was achieved by providing a shaft seal in which the stationary seal member is supported by, and is connected to, the stationary housing by a radially-extending elastomeric carrier, which is capable of flexing to ensure wear take-up resulting from use of the shaft seal.

The elastomeric carrier which is in the form cf an annular diaphragm is fixedly clamped in position at its outer peripheral edge and provided only a low face contact between the seal members in order to reduce wear and increase the working life of the shaft seal.

Further, the diaphragm was liable to distortion under low pressure conditions, for example 0.2 bar above atmospheric, with consequent unsatisfactory functioning of the diaphragm and shaft seal.

It is an object of the present invention to obviate or mitigate the above drawbacks and to provide an improved version of our aforesaid shaft seal.

According to this invention the shaft seal has the stationary seal member supported by, and connected to, a radially-extending flexible annular diaphragm, and the shaft seal is characterised by the provision of a radially-extending annular support plate of a radius substantially equal to the radial length of the annular diaphragm between its clamped peripheral edge and the stationary sealing member, and Ab the disposition of the stationary and rotating seal members relative to the annular support plate which is such that the annular diaphragm, in its initial assembled condition, is axially inclined out of face-to-face contact with the annular support plate save at its clamped peripheral edge.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a fragmentary half-sectional side elevation of a shaft seal according to the invention in its initial assembled condition; Fig. 2 is a similar view of the shaft seal in an operational condition; and Fig. 3 is a similar view of the shaft seal showing the seal members worn and requiring replacement.

Referring to the drawing the stationary housing of, for example a pump, is indicated by the reference 10 and the rotating shaft by the reference 11.

The shaft seal comprises a stationary sealing ring 12 and a rotatable sealing ring 13 in face-to-face rubbing contact.

The rotatable sealing ring 13 is supported in a carrier 14 of annular form through the intermediary of an annular elastomeric backing member 15 of L-shaped cross-section, which engages adjacent radial and axial faces of the rotatable sealing ring 13 which is bonded, welded or otherwise secured to the backing member 15 so that they operate (e.g. rotate) as a unit.

The carrier 14 is secured to a support ring 16 by axially extending pins 17 (only one shown).

The support ring 16 is, in turn, secured by axially extending pins 18 (again only one shown) to a shaft sleeve 19 rotatable with the shaft 11.

O-rings 20 and 21 are respectively disposed between the carrier 14 and the shaft sleeve 19 and the shaft sleeve 19 and the shaft 11 for sealing purposes.

The stationary sealing ring 12 is supported by a flexible elastomeric annular diaphragm 22 which extends radially of the shaft 11.

The annular diaphragm 22 defines an inner radial flange 23A which engages the radial surface of the stationary sealing ring 12 remote from the rotatable sealing ring 13 and an axial flange 23B intermediate the inner and outer circumferences of the annular carrier 22 which engages the external circumference of the stationary sealing ring 12.

The radial and axial flanges 23A and 23B of the annular diaphragm 22 are bonded, welded or otherwise secured in any convenient way to the adjacent radial and axial surfaces of the sealing ring 12.

The annular diaphragm 22 is clamped at its outer peripheral edge between the housing 10 and an annular frigid support plate 24, of metal for example, which is bolted to the housing 10 as indicated at 25 with the bolts 25 traversing the clamped edge of the annular diaphragm 22.

The effective radial length L1 of the annular support plate 24 is substantially equal to the radial length L2 of the annular diaphragm 22 between its clamped peripheral edge and the stationary sealing ring 12.

When the shaft seal is initially assembled around the shaft 11 the contact face line CF between the sealing rings 12 and 13 is disposed relative to the annular support plate 24 such that the annular diaphragm 22 is axially biased into an inclined disposition clear of face-to-face contact with the annular support plate 24 save at its clamped peripheral edge, or substantially so (see Fig. 1).

During operation (see Fig. 2) the annular diaphragm 22 is forced under pressure against the annular support plate 24 which serves to prevent bulging of the annular diaphragm 22 as was the case in the shaft seal disclosed in our aforesaid Patent Application.

There is a significant reduction in the face load due to the change in the balance line and hence a reduction in the area of pressure application as the area of face-to-face contact between the annular diaphragm 22 and annular support plate 24 increases radially inwardly from the clamped peripheral edge.

As wear occurs (see Fig. 3) the annular diaphragm 22 makes more and more face-to-face contact with the annular support plate 24 with consequential face load reduction. In the Fig. 3 condition the shaft seal needs replacement.

It is to be noted that the spring rate of the flexible annular diaphragm 22 is unaffected by the presence of the support plate 24.

It will be manifest that the radial disposition of the annular diaphragm 22 permits shortening of the overall length of the shaft seal compared with existing shaft seals and the fact that the annular diaphragm 22 is elastomeric in nature means that it will provide the necessary sealing ring contacting pressure and wear take up for the mechanical seal.

The annular diaphragm 22 may be radially compressed during assembly into the shaft seal to provide a low axial stiffness in the sealing ring supporting region of the diaphragm 22, namely the region defined by the flanges 23A and 23B.

Such low axial stiffness permits long axial travel of the sealing ring 12 in response to forces applied there against by, or through rhe intermediary of, the rotatable sealing ring 13 during mechanical seal operation.

It is also envisaged that radial stretching of the annular diaphragm 22 during assembly will provide the high axial stiffness and short axial travel for use in situations where radial length availability for the shaft seal is particularly short.

The word "elastomeric!! used herein is to be construed as including rubber, natural and synthetic, and any suitable plastics materials.

Claims (3)

CLAIMS:

1. A shaft seal comprising a rotary seal member for mounting on a rotatable shaft and a stationary seal member for mounting on a housing arranged around the rotatable shaft such that the rotary and stationary seal members are in face to face contact, the stationary seal member when mounted on the housing being supported by, and connected to, a radially-extending flexible annular diaphragm the peripheral edge of which is clamped to the housing, wherein the shaft seal is characterised by the provision of an annular support plate on a low pressure side of the diaphragm, the support plate extending radially inwards from the clamped peripheral edge of the annular diaphragm to adjacent the stationary seal member such that, in the initial assembled condition of the shaft seal, the annular diaphragm is inclined out of face to face contact with the annular support plate save at its clamped peripheral edge.

2. A shaft seal according to claim 1, wherein the stationary seal member is received between two axially extending annular flanges defined adjacent the radially inner edge of the annular diaphragm.

3. A shaft seal substantially as hereinbefore described with reference to Figures 1 to 3 or Figure 4 of the accompanying drawings.