GB2155120A

GB2155120A - Mechanical face seal

Info

Publication number: GB2155120A
Application number: GB08504931A
Authority: GB
Inventors: Samuel Clifford Walt Wilkinson
Original assignee: Crane Packing Ltd
Current assignee: Crane Packing Ltd
Priority date: 1984-03-03
Filing date: 1985-02-26
Publication date: 1985-09-18
Also published as: GB8504931D0; GB2155120B

Abstract

A mechanical face-seal includes a flexible tubular element (16) in the form of a bush, diaphragm or bellows unit which serves to provide a fluid-tight seal between a seal face member (15) and an associated component (10) whilst permitting relative axial movement there between; a resilient member (19) is interposed between the tubular element and the component, the resilient member being a close fit to the tubular member, so as to provide a secondary sealing element in the event that the tubular member is pierced, whilst permitting movement of the tubular member to accommodate relative movement of the seal face member and associated component. The resilient member may also provide a coolant/lubricant reservoir. <IMAGE>

Description

SPECIFICATION Mechanical face seals This invention relates to mechanical face seals and in particular to mechanical face seals in which the seal face member is sealed to its associated component by means of a flexible tubular element, for example a diaphragm or bellows unit.

With mechanical face seals of this type, the integrity of the rather vulnerable flexible tubular element presents problems. This is particularly so with the relatively small mechanical face seals located, for example, between the propeller shaft and stern tube in the bilge of a boat, where the flexible tubular element is liable to damage by debris in the bilge and, because they are not easily accessible, there is a serious risk that heavy leakage might occur before repair could be effected.

Another problem with this type of seal is to maintain the radial stability of the seal face member, also if the seal face member and flexible tubular element are mounted on a rotating component centrifugal force will cause the tubular element to distort which may reduce the axial loading between the sealing faces of the seal face member and seat.

According to one aspect of the present invention a mechanical face seal for providing a seal between a pair of relatively rotatable components comprises; a seat fixed both axially and rotationally, and sealed with respect to one of said components; a seal face member associated with said other component, said seal face member being fixed rotationally but movable axially of its associated component and being urged axially into sealing engagement with said seat; a flexible tubular member secured in fluid-tight manner, at one end to the seal face member and at the other end to the component associated with the seal face member, to provide a seal between the seal face member and its associated component and permit relative axial movement therebetween; and a resilient member interposed between the flexible tubular member and component associated with the seal face member, said resilient member fitting closely with the flexible tubular member.

With this construction, if the flexible tubular member is pierced, the resilient member will act as a secondary seal to reduce leakage. Furthermore the resilient member will heip control radial stability of the seal face member and distortion of the flexible tubular member.

The resilient member is preferably formed from an elastomeric sponge material and substantially fills the void between the flexible tubular member and component associated with the seal face member. The resilient member should be sufficiently resilient to maintain a close fit with the flexibe tubular member, but should not prevent the latter from distorting to permit axial movement of the seal face member to accommodate wear of the sealing faces. In many applications it is desirable to supply a liquid lubricant or coolant to the void between the flexible tubular member and the component associated with the seal face member. In these circumstances it is advantageous to form the resilient member from an open pored sponge or other absorbent material so that it will act as an emergency reservoir for the lubricant or coolant in case the supply is temporarily interrupted.The resilient member is preferably moulded to conform with the desired shape of the tubular member, this may be done prior to assembly or in situ.

The flexible tubular member may be made of an elastomeric or plastics material and may be in the form of a bush, diaphragm or bellows unit. Where the tubular member is made of a resilient material it may also be used to apply an axial load on the seal face member urging it into sealing engagement with the seat. Other spring means may however be used for this purpose or to reinforce the load applied by the tubular member. Alternatively or in addition to using these elements to load the seal face member, the resilient member may be arranged to apply an axial load on the seal face member.

An embodiment of the invention is now described, by way of example only, with reference to the accompanying drawing which illustrates in sectional side elevation, a mechanical face seal according to the present invention.

The accompanying drawing illustrates a propeller shaft seal for a small powerboat. The seal is fitted at the in-board end of the stern tube 11. The propeller shaft 10 passes through the stern tube 11 and is mounted therein on a rubber bearing 12.

An annular seat 13 is bolted to the in-board end of the stern tube 11 by means of a plurality of circumferentially spaced bolts 14, so that it surrounds the propeller shaft 10. A stout resilient rubber diaphragm unit 16 is mounted on the shaft 10 and is clamped thereto, at the end remote from the seat 13, by means of a clamping ring 17 which is secured by tangential bolts (not shown). The end of the diaphragm unit 16 adjacent the seat 13 carries an annular seal face member 15. The diaphragm unit 16 is clamped to the shaft 10 in a position such that the diaphragm unit 16 is compressed axially and the seal face member 15 is urged axially into sealing engagement with the seat 13.

The diaphragm unit 16, seal face member 15, seat 13 and portion of the stern tube 11 in-board of the rubber bearing 12, thereby provides a chamber 18. Water from the cooling system of the boat's engine is fed through inlet 20 into the chamber 18.

This water cools and lubricates the engaging sealing faces of the seat and seal face member 15 and also leaks down the stern tube 11 to lubricate the rubber bearing 12.

A moulded water absorbent sponge rubber ring 19 is located within the portion of chamber 18 defined by the diaphragm unit 16. This sponge ring 19 conforms closely with the internal surface of the diaphragm unit 16 and may be formed as a separate unit which is inserted into the diaphragm unit 16 during the assembly of the seal or may be moulded into the diaphragm unit 16.

The sponge ring 19 assists in maintaining the required shape of the diaphragm unit 16, whilst per mitting distortion thereof to load the seal face member 15 into sealing engagement with the seat 13 and allow for axial movement of the seal face member 15 as the seat 13 and seal face member 15 wear. The sponge ring 19 will also reduce leakage of fluid through the diaphragm unit 16, should it become cut or perforated. Some leakage will occur in view of the absorbent nature of the sponge ring 19. but this leakage will only be a fraction of that which would occur if there was only a diaphragm unit.

During normal operation, the sponge ring 19 will absorb some of the water that is introduced into the chamber 18 through inlet 20 and will thus become saturated. Should the supply of water to the chamber 18 be interrupted for some reason, the sponge ring 19 will then act as an emergency reservoir and, for a limited period, will feed sufficient water to the sealing faces of the seal face member 15 and seat 13 for cooling and lubricating purposes.

Various modifications may be made without departing from the invention. For example, while the ring 19 is formed from sponge rubber any material which will provide the required degree of resilience may be used. Also while diaphragm unit 16 is made of rubber, other flexible materials, for example other elastomers, plastics (eg PTFE) or even thin metal may be used. While in the above embodiment the ring 19 is made from absorbent sponge rubber so as to provide an emergency reservoir for coolant or lubricant, if this requirement is unnecessary the secondary sealing performance may be enhanced by the use of a closed pored sponge or pressure sponge.

Claims

1. A mechanical face seal for providing a seal between a pair of relatively rotatable components comprising; a seat fixed both axially and rotationally, and sealed with respect to one of said components; a seal face member associated with said other component, said seal face member being fixed rotationally but movable axially of its associated component and being urged axially into sealing engagement with said seat; a flexible tubular member secured in fluid-tight manner, at one end to the seal face member and at the other end to the component associated with the seal face member, to provide a seal between the seal face member and its associated component and permit relative axial movement therebetween; and a resilient member interposed between the flexible tubular member and component associated with the seal face member, said resilient member fitting closely with the flexible tubular member

2. A mechanical face seal according to claim 1 in which the resilient member is formed from an elastomeric sponge material.

3. A mechanical face seal according to claim 1 in which the sponge is open pored.

4. A mechanical face seal according to any one of claims 1 to 3 in which the resilient member substantially fills the void between the flexible tubular member and the component associated with the seal face member.

5. A mechanical face seal according to any one of claims 1 to 4 in which the resilient member is moulded to conform with the desired shape of the flexible tubular member.

6. A mechanical face seal according to any one of claims 1 to 5 in which the resilient member is arranged to apply an axial load to the seal face member.

7. A mechanical face seal for providing a seal between a pair of relatively rotatable components, substantially as described herein with reference to, and as shown in the accompanying drawing.