GB2218166A

GB2218166A - Jacking pipe seals

Info

Publication number: GB2218166A
Application number: GB8809321A
Authority: GB
Inventors: Thomas William Wildgoose
Original assignee: Victaulic Co PLC
Current assignee: Victaulic Co PLC
Priority date: 1988-04-20
Filing date: 1988-04-20
Publication date: 1989-11-08
Anticipated expiration: 2008-04-20
Also published as: GB2218166B; GB8809321D0

Abstract

The invention provides a seal 1 for a jacking pipe joint, and a joint between a pair of juxtaposed spigot 3 and socket jacking pipes wherein the spigot is provided on its outer periphery with an annular groove 2 having sharply defined shoulders 4,5 at each axial end thereof, the sealing member being in use tightly located within the groove, and the sealing member in its non-compressed condition bulging on its radially outer side in a curve 7 from each axial end to an area adjacent its axial centre point, and further the sealing member having shoulders 8,9 at each axial end thereof closely abutting the shoulders of the spigot groove. <IMAGE>

Description

Jacking Pipe Seals This invention relates to jacking pipe seals, and more specifically jacking pipe seals for jacking pipe arrangements utilizing interjack stations.

The pipe jacking technique is an increasingly popular method of installing pipe lines underground. The technique takes the place of earlier procedures of laying pipes into open trenches which are then filled and made good.

The technique essentially consists of forming an appropriately sized hole slightly larger than the pipes to be laid, by means of a boring machine. Pipes are then pushed behind the boring machine by means of large jacks, usually of hydraulic operation.

Essentially the form of pipe-joint construction of interest in relation to the present invention in connection with pipe jacking techniques is that in which one end of the pipe is at least internally enlarged in one way or another to form a socket, into which the spigot of an adjacent pipe is entered, sealing being provided by means of a resilient annular sealing member between the spigot and the socket, usually contained within a annular groove either within the socket or upon the spigot.

In such jacking techniques, in order to increase efficiency, smaller additional jacking units are positioned at intervals along the pipeline and, as more pipes are inserted into the bored tunnel, these are used to effect a series of small forward movements along the line. When the movement begins at the front of the drive, subsequent movements in series move the whole line without pressure from the main jacking unit. After this series of movements the main unit continues to jack pipes on the reduced load.

The smaller interjack movements have the effect of producing at the relevant joint between pipes in the pipeline, a series of reciprocations of each spigot within its respective socket, the spigot and socket joints being partially opened and closed many times. In practise this creates severe difficulties of operation for the sealing meter between the spigot and socket. Thus, in order to maintain the integrity of the interior of the pipeline during jacking, it is highly desirable that the seal be maintained during these reciprocations of the spigot within the socket, and also that the sealing member itself is not damaged by movement in either direction between the spigot and socket.

Previous proposals have included an '0' ring seal, which has good sealing properties but tends to be displaced with repeated reciprocation, and an anchored gasket, which is firmly located to prevent movement during repeated reciprocations but tends to suffer damage from the repeated movement and become less effective in sealing.

It is an object of the present invention to provide a sealing arrangement between the spigot and socket of a pair of juxtaposed jacking pipes which overcomes or at least substantially reduces the above-mentioned problems.

In accordance with one aspect of the present invention, there is provided a resilient annular sealing member for a spigot and socket jacking pipe joint, the sealing member being adapted to be fitted tightly within an outer annular groove in a pipe spigot, and comprising a radially outwardly extending bulbous portion curving outwardly from each axial end of the gasket, the sealing member being provided at each axial end with shoulders for abutting against corresponding shoulders of the groove in the spigot.

In accordance with another aspect of the present invention, there is provided a joint between a pair of juxtaposed spigot and socket jacking pipes wherein the spigot is provided on its outer periphery with an annular groove having sharply defined shoulders at each axial end thereof, and a sealing member tightly located within the groove, the gasket in its non-compressed condition bulging on its radially outer side in a curve from each axial end to an area adjacent its axial centre point, the sealing member having shoulders at each axial end thereof closely abutting the shoulders of the spigot groove.

The radially inner face of the sealing member is preferably provided with an annular recess to accommodate displaced gasket material during compression thereof.

The sealing member or gasket of the invention may be totally symmetrical about its axial centre plane so as to -provide identical sealing performance in both directions of the reciprocating motion of the intermittent jacking operation of the pipe and spigot and joints. The axial centre point of the outer periphery of the gasket will in this case be the point of highest stress when under compression and thus the most effective sealing position.

The outer peripheral surfaces on each side of this area of high stress are designed to "fall away" in that the outer peripheral surface of the gasket curves radially inwardly from the peak of the bulg. This creates a reduction in pressure and thus a reduction in friction between the gasket and the surface of the socket when carrying out the necessary reciprocating movements during intermediate jacking.

It is to be appreciated that to adjust the sealing capability of the gasket, the hardness of its rubber or synthetic rubber composition can be varied thus enabling a range of performance requirements to be met using one simple but effective cross-section.

The gasket will conveniently be stretch-fitted on to the spigot thus ensuring a firm tight fit in the outer peripheral groove to resist dislodgement of the gasket during movement between the associated spigot and socket.

By means of the invention, the pressure sealing capability of a joint at an intermediate jacking position is improved, and there is also provided a satisfactory ability to withstand friction and abrasion created by the multiple reciprocations.

The use of a balanced and symmetrical gasket in axial cross-section is particularly suitable for meeting the requirement for the performance of the gasket to be equally efficient in both the opening and the closing modes and movements of the jacking pipes at the intermittent jacking positions.

In one embodiment of the invention, pairs of seals may be used in each joint, a pair of axially spaced grooves being provided around the spigot into each of which a gasket is stretch-fitted. Such an arrangement provides the advantage of reducing the abrasion during normal operation, with the additional benefit of retaining one sealing surface should, for any reason, the other sealing surface fail prematurely.

In order that the invention may be more readily understood, one embodiment thereof will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a schematic cross-section of part of a concrete jacking pipe spigot carrying a sealing gasket in accordance with the invention; and Figure 2 is a schematic cross-section of part of the socket of one pipe and the interengaging spigot of another incorporating an intervening gasket in accordance with the invention Referring now to Figure 1, it is to be seen that an annular sealing gasket 1 of rubber is located within a groove 2 in a concrete pipe spigot 3. The gasket in cross-section is adapted to fit within the inclined walls 4, 5 of the groove tightly and with precision by means of side shoulders 8, 9, and will have been stretched into position within the groove 2. It is to be observed that the gasket is radially outwardly bulbous with a curved periphery reaching from the edges of the groove to the top of the bulb position. A radially inner recess or groove 6 is disposed around the gasket within the concrete pipe groove.

The sealing gasket is axially symetical about the highest point 7 which is thereof in use the point of highest stress and the most effective sealing portion.

The surface on each side of this high stress area falls away creating, in use, reduction in pressure and thus a reduction in friction between seal and the surface of the socket during movement in either direction during the intermediate jacking operation creating reciprocation between the spigot and socket.

Reference to Figure 2 will show the compressed disposition of the outer periphery 10 of the gasket when a socket is located thereabove. Even in this situation the stress distribution axially about the mid-point of the gasket is still the same, i.e. the high stresses are at more or less the centre point and fall away on either side. It is to be seen that the radially inner groove 6 in the gasket has, due to the compression of the gasket, decreased in volume.

It is manifest that the gasket, with its distribution of rubber on its outer periphery and its axial symetry is ideally suited for use in jacking pipes to be subjected to intermediate jacking operation. It can be said that the configuration of the gasket is very similar to an "anchored 0 ring" which therefore combines the advantages of the 0 ring and an anchored gasket without the disadvantages normally associated with either.

Claims

CLAIMS:

1. A resilient annular sealing member for a spigot and socket jacking pipe joint, the sealing member being adapted to be fitted tightly within an outer annular groove in a pipe spigot, and comprising a radially outwardly extending bulbous portion curving outwardly from each axial end of the gasket, the sealing member being provided at each axial end wlth shoulders for abutting against corresponding shoulders of the groove in the spigot.

2. A sealing member as claimed in Claim 1 wherein the radially inner face thereof is provided with an annular recess to accommodate displaced gasket material during compression of the sealing member.

3. A sealing member as claimed in Claims 1 or 2 wherein the member is symmetrical about its axial centre plane.

4. A joint between a pair of juxtaposed spigot and socket jacking pipes wherein the spigot is provided on its outer periphery with an annular groove having sharply defined shoulders at each axial end thereof, and a sealing member tightly located within the groove, the sealing member in its non-compressed condition bulging on its radially outer side in a curve from each axial end to an area adjacent its axial centre point, the sealing member having shoulders at each axial end thereof closely abutting the shoulders of the spigot groove.

5. A joint as claimed in Claim 4 wherein the radially inner face thereof is provided with an annular recess to accommodate displaced gasket material during compression of the. sealing member.

6. A joint as claimed in Claims 4 or 5 wherein the member is symmetrical about its axial centre plane.

7. A joint as claimed in Claims 4, 5 or 6 wherein the sealing member is stretch-fitted on to the spigot.

8. A joint as claimed in any one of Claims 4 to 7 wherein a pair of axially spaced grooves are provided around the spigot into each of which a sealing member is stretch-fitted.

9. A joint between a pair of juxtaposed spigot and socket jacking pipes substantially as shown in and as hereinbefore described with reference to the accompanying drawings.

10. A resilient annular sealing member substantially as shown in and as hereinbefore described with reference to the accompanying drawings.