GB2080891A

GB2080891A - Shaft seals

Info

Publication number: GB2080891A
Application number: GB8121188A
Authority: GB
Original assignee: Crane Packing Ltd
Current assignee: Crane Packing Ltd
Priority date: 1980-07-24
Filing date: 1981-07-09
Publication date: 1982-02-10
Also published as: GB2080891B

Abstract

In a mechanical face seal incorporating a bellows unit 16, an emergency sealing element 25 is located between a seal face member 15 and a retaining ring 20 and is arranged to prevent or control the leakage of fluid from a high pressure region to a low pressure region, in the event that a failure occurs in the bellows unit. The emergency sealing device also acts to centre the bellows and seal face member associated therewith radially with respect to the component upon which they are mounted and may also act as a dirt excluder. The sealing element 25 can be of deformable material and with sealing lips 26 as shown, or of rigid material and provided with a close clearance to the shaft 10. <IMAGE>

Description

SPECIFICATION Mechanical face seals 'this invention relates to mechanical face seals nd in particular mechanical face seals incorporating a bellows unit.

According to one aspect of the present invention a mechanical face seal for providing a seal between a pair of relatively rotatable components to separate a relatively high pressure fluid region frorn a relatively low pressure fluid region, comprises a first seal face member or seat which is secured to one of said components in a fluid-tight manner, a second seal face member which is secured and sealed to the other component by means of a bellows unit, the first and second seal face members being arranged so that sealing faces of the members are held in sealing engagement, and an emergency sealing element located between said second seal face member and its associated component and arranged to prevent or control the leakage of the fluid from the high pressure region to the low pressure region, in the event that a failure occurs in the bellows unit.

In addition to acting as an emergency seal, the emergency sealing element may also serve to locate the bellows and seal face member secured thereto radially, with respect to the component upon which they are mounted.

Furthermore the emergency seal may also act as a dirt excluder, preventing material entering and clogging the bellows.

The invention is now described, by way of example only, with reference to the accompanying drawing which shows diagrammatically a part sectional view of a mechanical face seal, formed in accordance with the present invention.

As illustrated in the accompanying drawing a mechanical face seal between a rotary shaft 10 and a housing 11 in, for example, a pump assembly, comprises a first annular seal face member or seat 1 2 which is retained in a recess in the housing 11 and is sealed thereto by means of an elastomeric '0' ring 1 3.

A second seal face member 15, made of sintered carbon, is located in a metal retaining ring 20, the sealing face 1 4 of said second seal face member 1 5 being urged into sealing engagement with an opposed sealing face on the seat 1 2 by means of a metal bellows unit f6 which also serves to create a fluid-tight seal between the second seal face member 1 5 and the shaft 10. The bellows unit 16 comprises a series of annular discs 21 which are welded together circumferentially, adjacent discs 21 being welded together alternately at their inner and outer peripheries, to form a series of convolutions.The bellows unit 1 6 is welded at one end 22 to the end of the retaining ring 20 which is remote from the seal face member 1 5 and at the other end 23 to a collar 17, which is secured to the shaft 10 by means of a series of radially disposed grub screws 24 and is sealed thereto by means of an '0' ring 18.

An emergency sealing element 25, in the form of an annular disc made of PTFE, is mounted about the shaft 10 and is sealed thereto by means of a pair of lips 26 on its inner circumference. The sealing element 25 projects radially outwardly from the shaft 10 and into a recess formed by a radially inwardly directed flange 27 on the retaining ring 20 and the rear face 28 of the seal face member 1 5. The portion of the sealing element 25 which is opposed to the face 28 of the seal face member 1 5 is provided with a corresponding sealing face 29.By this means, in the event that the bellows unit 1 6 fails and high pressure fluid is permitted to pass through the bellows unit 1 6. the fluid will force the emergency sealing element 25 towards the seal face member 1 5 and the faces 28 and 29 will be forced into sealing engage ment, thereby preventing escape of fluid from the high pressure region P.

The outer periphery 30 of the sealing element 25, projects into close proximity or abutting relationship with a co-axial surface 31 of the retaining ring 20. By this means the sealing element 25 also serves to locate the bellows unit 16, retaining ring 20 and seal face member 15, radially with respect to the shaft 10.

Under normal operating conditions, as the emergency sealing element 25 rotates in unison with the shaft 10, bellows unit 16, retaining ring 20 and seal face member 15, there will be no relative movement between these parts and consequently there will be no wear on the lips 26, sealing face 29 or outer periphery 30 of the sealing element 25.

The emergency sealing eiements of the present invention may be made of a deformable material such as PTFE or rubber or alternatively from a more rigid material such as sintered carbon.

Where deformable materials are used, the emergency sealing element may be arranged to deform, under the influence of the pressure of the fluid to which it will be exposed upon failure of the bellows unit, so that it comes into sealing engagement with the second seal face member. Alternatively the sealing element may be slidably mounted on the component associated with the second seal face memeber so that the pressure of the fluid will move it into contact with the second seal face member.

As described above, when the emergency sealing element is made of deformable material, one or more sealing lips 26 may be provided to seal the element to the associated component 10. Similar sealing lips may be provided to engage the seal face member 15, in place of the sealing face 29 or to engage the surface 31. In an alternative embodiment, the emergency sealing element 25 may be slidingly located on the shaft 10, with a close clearance.

Where rigid materials are used, the emergency sealing element must be arranged to slide on the component associated with the second seal face member so that it will slide into engagement with the second seal face member, under the influence of the pressure of fluid to which it is exposed on failure of the bellows unit. This may be done by providing a close clearance between the component and the emergency sealing element.

Whichever method is used to mount the emergency sealing element with respect to the associated component, it should be capable of movement with the seal face member, relative to the component, in order to take account of wear between the sealing faces of the seal face members, and any resistance to such movement should easily be overcome by the force applied by the bellows unit or other means of loading the seal face members.

The emergency sealing element according to the present invention may be used either as a restrictor to control the escape of pressurised fluid or as a seal to prevent the escape of pressurised fluid, in the event of a bellows failure.

Various modifications may be made without departing from the invention, for example while it is normal practice to secure the beW lows unit and seal face member attached thereto, to the rotating component, these and the emergency sealing element associated therewith may be attached to the stationary component.

The bellows unit of the present invention may be formed from metal or other similar rigid resilient material for example a rigid plastics material, or from elastomeric materials. The bellows may be formed by welding as described above, by deforming a tubular blank or by any other appropriate means.

While in the above description the seal face member 1 5 was made of sintered carbon, both this seal face member and the first seal face member or seat 12 may be made of any suitable material. Furthermore, alternative methods may be used to secure the bellows unit 1 6 to the seal face member 1 5 and the associated component. For example, the retaining ring may be dispensed with and the seal face member may be secured directly to the bellows unit. Also instead of welding the ends of the bellows unit to its associated components, other methods, for example, swaging or brazing, which produce fluid-tight joints, may be used.

Claims

1. A mechanical face seal for providing a seal between a pair of relatively rotatable components to separate a relatively high pressure fluid region from a relatively low pressure fluid region, comprising a first seal face member or seat which is secured to one of said, components in a fluid tight manner, a second seal face member which is secured and sét to the other component by means of a bellows unit, the first and second seal face members being arranged so that sealing faces of the members are held in sealing engagement, and an emergency sealing element located between said second seal face member and its associated component and arranged to prevent or control the leakage of fluid from the high pressure region to the low pressure region, in the event that failure occurs in the bellows unit.

2. A mechanical face seal according to Claim 1 in which the emergency sealing ele ment is arranged so that it will be moved into sealing contact with the second seal face member, under the influence of the pressure of the fluid to which it is exposed upon failure of the bellows unit.

3. A mechanical face seal according to Claim 1 or 2 in which the emergency sealing element is slidable with respect to the component associated with the second seal face member, so that it may be moved into sealing contact with the second seal face member under the influence of the pressure of fluid, to which it is exposed upon failure of the bellows unit.

4. A mechanical face seal according to Claim 1 or 2 in which the emergency sealing element is arranged so that it is deformed into sealing engagement with the second seal face member, by means of the fluid pressure to which it is exposed upon failure of the bellows unit.

5. A mechanical face seal according to any one of Claims 1 to 4, in which the emergency sealing element is sealed to the component associated with the second seal face member.

6. A mechanical face seal according to any one of the preceding Claims in which the emergency sealing element is made of a flexible material.

7. A mechanical face seal according to Claim 6 in which the emergency sealing element is made of PTFE or an elastomeric composition.

8. A mechanical face seal according tQ Claims 6 or 7 in which the emergency sng element is provided with a sealing lip to engage the second seal face member.

9. A mechanical face seal according to Claim 6 or 7 in which the emergency sealing element is provided with a sealing face to engage a corresponding sealing face on the second seal face member, upon failure of the bellows unit.

10. A mechanical face seal according to Claim 6, 7, 8 or 9 in which the emergency sealing element is provided wffi orie or more sealing lips to engage the component associ ated with the second seal face member.

11. A mechanical face seal according to any one of Claims 1-5 in which the emeragency sealing element is formed from a rigid ,,material, a sealing face on the emergency sealing element being arranged to make seal ing engagement with a corresponding face on the second seal face member, upon failure of the bellows unit.

12. A mechanical face seal according to Claim 11 in which the emergency sealing element is formed from sintered carbon.

13. A mechanical face seal according to any one of the preceding Claims in which the emergency sealing element engages or ex tends into close radial proximity to, a surface on or secured to the second seal face mem ber, said surface being co-axial with the com ponent associated with the second seal face member so that the emergency sealing ele ment serves to locate the second seal face member and bellows unit radially with respect to the component with which they are associ ated.

14. A mechanical face seal substantially as described herein with reference to, and as shown in the accompanying drawing.