GB2300029A - Seal assembly - Google Patents

Abstract

A seal assembly 15 for sealing a shaft 11 rotatably mounted in a housing 12, the seal assembly including annular seal means comprising one or more O-ring type seals 21 located between a pair of axially spaced seal faces 30, 31, clamp means 24 surrounding the O-ring seal(s) for radially compressing the O-ring seal(s) to cause the O-ring seal(s) to sealingly engage the shaft, the seal faces being axially movable relative to one another, and resilient biasing means 60 for resiliently biasing the seal faces toward one another to sealingly engage opposed axial ends of the annular seal means. The assembly allows axial wear on the seal faces to be accommodated.

Description

SEAL ASSEMBLY The present invention relates to a seal assembly, in particular a seal assembly for sealing a rotating shaft.

According to one aspect of the present invention there is provided a seal assembly for sealing a shaft rotatably mounted in a housing, the seal assembly including annular seal means comprising one or more O-ring type seals located between a pair of axially spaced seal faces, clamp means surrounding the O-ring seal(s) for radially compressing the O-ring seal(s) to cause the O-ring seal(s) to sealingly engage the shaft, the seal faces being axially movable relative to one another, and resilient biasing means for resiliently biasing the seal faces toward one another to sealingly engage opposed axial ends of the annular seal means.

In one embodiment, each seal face is movable in the axial direction and the resilient biasing means acts to move each seal face.

In another embodiment, one of the seal faces is static in the axial direction and the other seal face is movable in the axial direction, the biasing means acting to move said other seal face and said seal means toward the static seal face.

Various aspects of the present invention are hereinafter described with reference to the accompanying drawings, in which: Figure 1 is a part axial section through a shaft seal assembly according to a first embodiment of the present invention; Figure 2 is a part axial section through a shaft seal assembly according to a second embodiment of the present invention; Figure 3 is a part axial section through a shaft seal assembly according to a third embodiment of the present invention.

Referring initially to Figure 1 there is shown a shaft 11 which is rotatably mounted in a housing 12. The housing 12 may for example be the housing of a pump and the shaft 11 may be a drive shaft on which a pump impeller is mounted.

The shaft 11 is sealed with respect to the housing 12 by a seal assembly 15 according to the present invention.

The seal assembly 15 includes an annular seal means 20 comprising a pair of side by side O-ring seals 21. An annular clamp member 24 surrounds the O-ring seals 21 and is arranged to compress the seals 21 in the radial direction to seal upon the shaft 11 and to also grip the shaft 11. The degree of grip between the seals 21 and shaft 11 is such as to restrain axial movement of the seals 21 along the shaft under normal operating conditions. Accordingly, the seal means 20 rotates in unison with the shaft. The clamp member 24 may be in the form of a contractable rigid collar or a contractable flexible, in-extensible band.

The seal assembly 15 further includes a pair of axially opposed seal faces 30, 31 inbetween which the annular seal means 20 is located. The seal faces 30, 31 each sealingly engage opposed axial ends of the annular seal means 20 and are connected to the housing 12 so as to be rotationally restrained. Accordingly, the seal faces 30, 31 form a sliding contact with the seal means 20 as the latter rotates with the shaft.

The seal face 30 is formed on an annular seal member 34 which forms part of an annular mounting assembly 40. The seal member 34 is formed from a wear resistant rigid material, preferably a metal such as steel.

The mounting assembly 40 includes a rigid annular mounting plate 41 carrying on its outer face an annular resilient plate 43. The plate 41 is preferably made from steel and plate 43 is preferably made from an elastomeric material such as a natural or synthetic elastomer. The plate 43 may have a thickness in the range of 5-30 mm, more preferably about 10-12 mm.

The plate 41 is preferably bonded to plate 43 to define a single unit and to provide a seal between plates 41, 43.

The unit defined by plates 41, 43 is secured to the housing 12 by bolts 47 (only one shown in the drawings) spaced circumferentially about the annular plate 41. The inner face 41a of plate 41 is sealed against the wall of the housing using a suitable gasket or mastic compound.

A series of bolts 50 are secured to the unit defined by plates 41, 43 and to project axially therefrom. The bolts 50 are circumferentially spaced about the plates 41, 43 and pass through bores 53 formed in a seal plate 52. The seal plate 52 is thereby slidingly supported on the bolts 50 for sliding movement in the axial direction of shaft 11. Seal plate 52 has an end face 54 which defines said seal face 31 and is made from a suitable rigid, wear resistant material. Preferably plate 52 is made from a suitable metal such as steel.

Biasing means 60 are provided for resiliently biasing plate 52 in an axial direction toward plates 41, 43 so as to resiliently bias the seal face 31 into contact with one axial end of seal means 20. Preferably the biasing means 60 comprises a series of spring washers 61, such as Belville springs, located on each bolt 50 and which are placed under a predetermined compression by an adjustable nut 65 screw threadedly received on the bolt 50.

Accordingly, as wear takes place between the seal means 20 and seal face 31 sealing contact is maintained by virtue of the biasing means 60 maintaining contact between plate 52 and sealing means 20.

As stated above, the seal means 20 does not move axially relative to the shaft 11 under normal operating conditions. Accordingly, the biasing means 60 do not act to resiliently urge the sealing means 20 in a direction toward seal face 30.

Sealing contact between seal face 30 and sealing means 20 is maintained by resiliently urging seal face 30 in an axial direction toward plate 52.

This is primarily achieved by compressing the portion of resilient plate 43 located inbetween seal member 34 and plate 41 by pressing the seal means 20 axially toward housing 12 prior to operating clamp member 24 to compress the seal means 20 to grip the shaft 11. Accordingly, after operating clamp member 24, seal means 20 is unable to move axially away from the housing 12 and so the plate 43 remains under compression and thereby resiliently urges face 30 in an axial direction toward seal means 20. Thus as wear takes place between face 30 and the seal means 20, the face 30 is moved axially under the resilient bias of plate 43 to maintain sealing contact.

Preferably, as shown in Figure 1, each bolt 50 has an enlarged head 57 which is located in a blind bore 58 formed in plate 43. The heads 57 of the bolts are arranged to lie inbetween the plate 41 and seal member 34 and thereby serve to transmit a portion of the biasing force generated by biasing means 60 to the seal member 34 for urging it in a direction toward seal means 20. The biasing force transmitted by the heads 57 serves to supplement the resilient biasing force generated by the compressed plate 43.

Alternatively, the bolts 50 may be secured to the plate 41 such that the resilient bias on seal member 34 is solely due to the compressed plate 43.

It is envisaged that, as shown in broken lines, bolts 47 may be axially extended and plate 52 radially extended to be slidingly secured on the extended bolts 47. Such an arrangement serves to assist parallel guidance of plate 52 as it moves axially.

A second embodiment 100 is illustrated in Figure 2 wherein components similar to those in Figure 1 have been designated by the same reference numerals.

In embodiment 100, bolts 50 are secured to plate 41 and they each extend through bores 80 formed in plate 43. Biasing means 90, preferably in the form same as biasing means 60, are provided, housed in each bore 80, for biasing seal member 34 towards seal means 20. Accordingly, biasing means 90 is preferably in the form of a series of spring washers 61.

For both embodiments it will be appreciated that seal member 34, plate 52 and seal means 20 may move in unison a small distance in both axial directions due to both seal member 34 and plate 52 being axially movable.

Accordingly the seal assembly can accommodate axial oscillations of the shaft 11 as for example may occur at start-up.

In addition, due to both seal member 34 and plate 52 being independently biased toward one another, sealing contact is automatically maintained between seal means 20 and faces 30, 31 without the need for adjustment as wear takes place.

It is envisaged that the biasing means 60, 90 may be in the form of helical compression springs or blocks of resilient material.

In the embodiments described and illustrated with respect to Figures 1 and 2, the clamp member 24 preferably acts to urge the seal assembly 20 to grip the shaft 11 so as to restrain axial movement therebetween.

Accordingly, each seal face 30, 31 is provided with independent biasing means for biasing the respective seal face into axial contact with the seal assembly 20.

An alternative embodiment 200 is illustrated in Figure 3 wherein the clamp member 21 acts to deform the seal assembly 20 to sealingly engage the shaft 11 but still permit some axial movement therebetween.

In embodiment 200 seal face 30 is static and is preferably formed by an end wall 241 of a housing 210.

A single biasing means 60 acts upon the seal plate 52 to axially urge the seal plate 52 toward the seal face 30, the degree of bias generated by the biasing means 60 being chosen to exceed sliding friction between the seal assembly 20 and shaft 11 such that the seal assembly 20 is also urged to move axially toward the seal face 30. Accordingly the biasing means 60 in embodiment 200 acts to urge both seal faces 30, 31 into axial engagement with the seal assembly 20.

Preferably the biasing means 60 in embodiment 200 comprises a series of circumferentially spaced compression springs 261. The springs 261 are located between the plate 52 and a compression plate 255 which forms an end wall of the housing 210.

Preferably the compression plate 255 is axially movably mounted in the housing 210 so as to enable the degree of biasing force generated by biasing means 60 to be adjusted. In this respect, the plate 255 has a screw thread formation formed about its periphery and is screw threadedly received within a tubular sleeve 211 which forms a side wall of the housing 210. Locking means 230 are preferably provided to retain the plate 255 at a desired axial position.

It is envisaged that for all embodiments the seal means 20 may comprise a single O-ring seal or more than two side by side O-ring seals.

It is also envisaged that the O-ring seals may be split to enable the seals to be radially located onto the shaft.

The seals 21 are made from a rigid yet deformable material such that the clamp 24 is able to deform the material of the seals 21 to sealingly grip the shaft 11. Suitable materials are, for example, plastics such as polytetrafluoroethylene, polyamides which may be filled, or soft metals such as copper or alloys.

Claims (4)

1. A seal assembly for sealing a shaft rotatably mounted in a housing, the seal assembly including annular seal means comprising one or more O-ring type seals located between a pair of axially spaced seal faces, clamp means surrounding the O-ring seal(s) for radially compressing the O-ring seal(s) to cause the O-ring seal(s) to sealingly engage the shaft, the seal faces being axially movable relative to one another, and resilient biasing means for resiliently biasing the seal faces toward one another to sealingly engage opposed axial ends of the annular seal means.

2. A seal as claimed in claim 1 wherein each seal face is movable in the axial direction and the resilient biasing means acts to move each seal face.

3. A seal as claimed in claim 1 wherein one of the seal faces is static in the axial direction and the other seal face is movable in the axial direction, the biasing means acting to move said other seal face and said seal means toward the static seal face.

4. A seal substantially as described herein with reference to one or more of Figures 1 to 3.