MECHANICAL SEAL

Abstract: A mechanical seal incorporates a metal bellows arrangement (1) which has a bellows unit (3) located between first and second end rings (5 and 7). The first end ring carries a seal face (9) and the second end ring is attached to a further seal component (11). The second end ring is associated with a sealing ring (17, 19) which is located between the second end ring and the other seal component. The second end ring is shaped to accommodate the sealing ring in a plurality of different cross-sectional shapes.

Description: MECHANICAL SEAL FIELD OF THE INVENTION This invention relates to mechanical seals and, in particular, mechanical seals with bellows units. BACKGROUND OF THE INVENTION A mechanical seal comprises a "floating" component which is mounted around a rotatable shaft for axial movement relative thereto. The rotatable shaft may be that of, for example, a pump. The seal includes a "static" component which is axially fixed, typically being secured to a housing. The floating component has a flat annular end face (seal face) directed towards a corresponding seal face of the static component. The floating component is urged, usually by means of one or more springs, towards the static component to close the seal faces together to form a sliding face seal. In use, one of the floating and static components rotates and is termed the rotary component. The other of the floating and static components does not rotate and is termed the stationary component. A seal whose floating component is rotary is described as a rotary seal. If the floating component is stationary, the seal is a stationary seal. If the sliding seal between the rotary and stationary components is assembled and pre-set prior to despatch from the manufacturer, the seal is termed a "cartridge seal". If the seal is despatched by the manufacturer in unassembled form, the seal is termed a "component seal". As mentioned above the floating component is generally axially energised by the use of at least one spring member. However, bellows units are often employed and they axially energise a mechanical seal face without the requirement for a dynamic, moving elastomer. This is an advantage in high temperature applications as the elastomer often limits the extent to which the seal can operate successfully. The in the bellows unit also facilitate heat dissipation within a barrier fluid system commonly employed with mechanical seals. Such heat dissipation, due to the large surface area of the bellows unit, helps to prolong seal survival. Typically, a metal bellows arrangement has a bellows unit welded to and located between first and second end rings. One of said end rings carries the seal face and the other is attached to some other seal component, thereby anchoring the bellows arrangement within the seal. For instance, in a rotary seal, the bellows arrangement may be anchored to the rotable shaft in a component seal and to the sleeve in a cartridge seal. Some form of sealing ring is required between the anchored end ring and the component to which it is attached. In many cases the sealing ring is an elastomer in the form of an O-ring. Such a sealing ring is adequate for many applications. However with seals exposed to extreme conditions of, for instance, speed and/or temperature, an O-ring is not sufficiently robust. In such cases a seal in the form of a grafoil wedge is typically used. Such a seal may have approximately the same inner and outer diameter as the O-ring but has a greater axial length and is wedged-shaped with its inner axial length greater than its outer axial length. In known metal bellows seals, the anchored end ring is shaped to accommodate either an O-ring or a grafoil wedge. Accordingly stocks of metal bellows arrangements have to include both those for use with O-rings and those for use with grafoil wedges. The metal bellows arrangements are very expensive. Furthermore, if in practice, it is found that the seal incorporating an O-ring is not suitable, then the metal bellows arrangement has to be removed and replaced by one which can accommodate a grafoil wedge. There is a need for a metal bellows seal which has greater flexibility with regard to the use of the metal bellows arrangement and seals associated therewith. STATEMENTS OF INVENTION According to the present invention there is provided a mechanical seal incorporating a metal bellows arrangement having a bellows unit located between first and second end rings, said first end ring carrying a seal face and said second end ring anchoring the arrangement to another seal component, said second end ring having associated therewith a sealing ring located between said second end ring and said another seal component, said second end ring being shaped to accommodate said sealing ring in a range of different cross-sectional shapes. Preferably the mechanical seal is a rotary seal although it should be understood that the invention may be applied to a stationary seal. A mechanical seal in accordance with the present invention may be of the component type or of the cartridge type. BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings are as follows:- Figure 1 shows the bellows arrangement of a known seal with an O-ring; Figure 2 shows the bellows arrangement of a known seal with a grafoil wedge; Figure 3 shows the cartridge mechanical seal of the invention having an O- ring; Figure 4 shows a cartridge mechanical seal of the invention having a grafoil wedge; Figure 5 shows a component seal of the invention having an O-ring; and Figure 6 shows a component seal of the invention having a grafoil wedge. DETAILED DESCRIPTION OF THE INVENTION Embodiments of the present invention will now be described, by way of examples only, with reference to the accompanying drawings. Figures 1 and 2 of the accompanying drawings show the bellows arrangements of a known seal. In each case the bellows arrangement 1 is provided with a bellows unit 3 which is welded to end rings 5 and 7. End ring 5 carries the seal face 9 and end ring 7 is attached to a further seal component 1 1 which may itself be attached directly to a drive shaft 13 in the case of a component seal or be attached to or form part of a sleeve 15 in the case of a cartridge seal. Bellows arrangement 1 is made out of stainless steel and is a relatively expensive item. As illustrated in Figures 1 and 2, the end rings 1 are differently shaped according to whether they are associated with an O-ring 17 or a grafoil wedge 19, each of which provides sealing between the bellows arrangement and the structure to which it is fixed. Accordingly it is necessary to carry stocks of both bellows arrangements so that the appropriate one can be chosen for use with an O-ring or a grafoil wedge according to the operating conditions. Referring to Figure 3 of the accompanying drawings, there is illustrated a cartridge seal having a sleeve 21 located about a pump shaft 23. The rotary components include a bellows arrangement 25 including a bellows unit 27, a first end ring 29 carrying seal face 31 and a second end ring 33 which is attached to end flange 35 of seal 21 by means of screws 37. Sleeve 21 is profiled to accommodate a first O-ring 39 in sleeve recess 41, this O- ring providing sealing between sleeve 21 and the shaft 23. A second, outwardly facing recess 43 in sleeve 21 accommodates a second O-ring 45 which bears against the inner surface of end ring 33. It will be seen that end ring 33 is broadly wedge-shaped at least adjacent bellows unit 27 where the inner diameter decreases in a direction towards sleeve flange 35. Sleeve 21 is correspondingly shaped in this region. Extending towards flange 35 from the wedge-shaped portion of ring 33 is a constant diameter portion against the inner surface of which O-ring 45 bears. Referring now to Figure 4 of the accompanying drawings, there is shown essentially the same cartridge seal but with a small number of components changed so that the seal operates with a grafoil wedge seal 51 in substitution for the O-ring 45. Importantly, the end ring 33 is not substituted, the same end ring being used whether the seal is an O-ring or a grafoil wedge. What is changed is the sleeve 21 which, at its left hand end (as viewed in Figure 4), is shaped to accommodate the inner surface of the grafoil wedge. At its other end, sleeve 21 is shaped to accommodate a further grafoil wedge which, in this case, provides the sealing between the sleeve and the shaft 23. It will be appreciated that, although the sleeve 21 is changed between the two situations, as depicted in Figures 3 and 4, this is a relatively cheap component as compared to the expensive bellows arrangement. Referring to Figure 5 of the accompanying drawings, there is illustrated a bellows arrangement used in connection with a component seal and incorporating an elastomer O-ring 61. In this case, the O-ring bears directly against the shaft 63 and the space between the wedge shaped portion of ring 65 and shaft 63 is occupied by a small ring of triangular cross-section. Referring to Figure 6 of the accompanying drawings, there is illustrated the bellows arrangement for a component seal in which sealing is provided by a grafoil wedge 71. It will be seen that the grafoil wedge occupies the entire space between end ring 65 and the shaft 63 and, accordingly, the same bellows unit can be used in the Figures 5 and 6 situations. Indeed, the only change that is required is the incorporation of the small triangular cross-section ring 67 in the case where an O-ring is to be used.

Claims: CLAIMS 1. A mechanical seal incorporating a metal bellows arrangement having a bellows unit located between first and second end rings, said first end ring carrying a seal face and said second end ring anchoring the arrangement to another seal component, said second end ring having associated therewith a sealing ring located between said second end ring and said another seal component, said second end ring being shaped to accommodate said sealing ring in a range of different cross-sectional shapes. 2. A mechanical seal according to Claim 1 in the form of a rotary seal. 3. A mechanical seal according to Claim 1 in the form of a stationary seal. 4. A mechanical seal according to any of the preceding claims which is of the component type. 5. A mechanical seal according to any of Claims 1 - 4 which is of the cartridge type. 6. A mechanical seal according to any of the preceding claims wherein the sealing ring has a substantially circular cross-section. 7. A mechanical seal according to any of Claims 1 - 6 wherein the sealing ring is substantially wedge-shaped.

Inventors: RODDIS ALAN, RODDIS, ALAN
Applicants: AES ENG LTD, RODDIS ALAN, AES ENGINEERING LIMITED, RODDIS, ALAN
Application year: 2000
Main classification: F16J15
IPC codes: F16J15