GB2400153A

GB2400153A - A pipe fitting for use in making a branch connection

Info

Publication number: GB2400153A
Application number: GB0406152A
Authority: GB
Inventors: Ralph Potter
Original assignee: POTABLE PIPE FITTINGS Ltd
Current assignee: POTABLE PIPE FITTINGS Ltd
Priority date: 2003-03-18
Filing date: 2004-03-18
Publication date: 2004-10-06
Also published as: EP1646821A1; GB0406152D0; GB0306196D0; WO2004083708A1

Abstract

A pipe fitting, such as a ferrule strap, arranged to be fitted to a primary pipe comprises two semi-circular parts 11, 12 arranged together to fit around the primary pipe 2 and fixing means, such as tapered wedges 13, 14 are arranged to fix the respective edges of the semi-circular parts 11, 12 together to cause the fitting 1 to grip the pipe 2. Each semi-circular part 11, 12 is formed from an outer layer of a first material which is adapted to flex to adapt to the cross-sectional shape of the pipe 2 while carrying the stress necessary for the fitting 1 to grip the pipe 2, and an inner layer 15 of a second material arranged, in use, to contact the external surface of the pipe 2 and to distribute the force applied by the outer layer across the surface of the pipe 2. In use one of the semi circular parts 11, 12 is preferably arranged to cooperate with a hole 21 of a predetermined size in the pipe 2 so that a branch connection can be made therefrom. A sensor can be provided to measure the contact pressure between the fitting 1 and the pipe 2. The first layer is preferably stainless steel while the second layer is preferably EPDM rubber.

Description

2400 1 53 PIPEWOR1( The present invention relates to fittings for pipes.

It is of particular relevance in the utilities industry, for instance the distribution of mains water or gas supplies, where it is desired to create a branch from a mains supply pipe.

As is well known, utility companies distribute water and gas from a mains network of pipes which are arranged to pass close to where points of supply are likely to be required. For instance, a mains water pipe may run under the ground along a residential street. It is necessary to take a branch pipe (commonly known as a service connection) from the mains pipe to each required point of supply, for example each house along the street, and for this purpose an arrangement is required which can create a junction to a branch pipe at any point along the mains pipe.

Historically, when the main pipes were typically made of iron, it was possible simply to tap directly into the pipe. However, subsequent materials have made such direct tapping into me fabric of the pipe impossible without problems of major leakage and, therefore, the technology of ferrule straps has been developed.

Essentially a ferrule strap is an item arranged to grip around the mains pipe covering and sealing around a hole made in that pipe for the purpose of providing the branch and also providing a fitting onto which the branch can be fitted.

One particular type of ferrule strap in the context of which the present invention has been developed, but to which it is not limited, is that of a self-tapping ferrule strap. In this arrangement, the fitting on the ferrule strap is configured to include a part which can cut a hole in the wall of a plastics pipe after the strap has been fitted to the pipe such that, in use, the strap can be fitted together with at least some of the associated branch pipe work after which the hole can be cut and the cutter is typically withdrawn from the pipe but retained within the fitting so that no leakage occurs during the fitting of the branch pipe work. This operation can be carried out while the pipe is under pressure and without disrupting supply to other users.

Generally speaking, the ferrule strap is constructed of two parts each of which has a generally semicircular cross section sized to fit around the external diameter of a mains pipe and some form of fixing by which the edges of the two parts of the strap can be fixed together to form a generally circular cross section arrangement which can be fitted to and tightened around the exterior of the pipe. Typically the fitting for the branch pipe work would be provided in the centre of one of the two semicircular parts.

In one of the most basic forms of ferrule strap, the fixing means to hold the two parts of the strap together may simply comprise a nut and bolt on each side which would be tightened up by an installer to fix the strap in position.

Other proposals for the manufacture of such ferrule straps have included proposals to form the entire device of plastics and to fix the two parts of the strap together by means of items known in the art as wedges. Essentially the ends of the two parts of the strap are provided with flanges over which a fixing member can be caused to slide in the axial direction of the pipe. Fixing members on each side of the pipe overlapping the flanges therefore hold the strap together. To allow for tightening of the strap it is known that these flanges, and correspondingly the wedges, can be tapered whereby the strap is fixed more tightly the more the wedge is pushed onto the fitting.

Typically also, the ferrule straps in the prior art include an O ring or other circular seal which is located around the hole made in the mains pipe in order to provide the seal around that hole.

A number of problems have been identified with the use of such prior art ferrule straps, in particular in the context of their use with modern plastics piping, which problems are exacerbated as the plastics pipes are developed with stronger materials and therefore thinner walls.

The problems essentially arise due to tightening of the ferrule straps onto the pipes to the wrong degree. With the first type of ferrule strap mentioned above where the tightening is effected by a simple nut and bolt arrangement, typically with the ferrule strap being made of gun metal, over tightening of the strap can easily occur where an installer desires to tighten the strap sufficiently to ensure that the O ring seal is secure. In such circumstances however the over tightening can cause deformation of the plastics pipe which may result in the later development of cracks and leaks in particular starting from the edges of the parts of the strap, or the straps themselves have been known to break.

Additionally, such straps are not able to conform to any lack of exact roundness of the primary pipe which again leads to uneven distribution of pressure on the outside of the pipe and further contributes to failure.

It is also found that under tightening of the ferrule strap can also cause problems of leakage. It has been found that, even where the strap is tightened sufficiently to cause a proper seal of the O ring around the hole drilled in the plastic mains pipe, it may be the cause that the tension in the walls of the plastic pipe caused by the pressurization of the water supply inside can be sufficient to cause cracks to propagate from the edges of the hole drilled in the pipe to cause leaks in the pipe over a period of time. Such problems are particularly likely to occur in the abovementioned plastics ferrule straps where the design of the strap may not provide significantly more resistance to strain than the plastics material forming the pipe itself.

The present invention provides a pipe fitting arranged to be fitted to a primary pipe, the fitting comprising two substantially semi-circular parts adapted to be arranged together to fit around the primary pipe and fixing means arranged to fix the respective edges of the semi-circular parts together to cause the fitting to grip the pipe, said semi-circular parts being formed of an outer layer of a first material and which is adapted to flex whereby to adapt to the cross-sectional shape of the primary pipe while carrying the stress necessary for the fitting to grip the pipe, and an inner layer of a second material arranged to contact the external surface of the pipe, in use, and to distribute the force applied by said outer layer across the surface of said pipe.

In this arrangement, a good fit is obtained to the primary pipe because, unlike prior arrangements, the fitting is strong enough to grip the pipe to the required degree while also adapting to the shape of the pipe whereby to distribute the forces applied to the pipe more evenly which reduces failure of the fitting and pipe combination.

In a principal embodiment the pipe fitting is a ferrule strap comprising a branch fitting in one of said semi-circular parts arranged to cooperate, in use, with a hole of a predetermined size in said primary pipe to provide a branch therefrom.

Preferably in this arrangement a portion of said inner layer is shaped to provide a seal around said hole.

In general terms, the first material typically has a higher stiffness or modulus than said second material, and preferred example materials for the first and second materials are stainless steel and EPDM rubber.

A further preferred and advantageous feature of the invention is that the fixing means is adjustable whereby the force with which the fitting, in use, grips the pipe is selectable or adjustable. This enables the fitting to be fitted in an optimum fashion, avoiding being either under- or overtightened whereby to improve its performance.

In this context, the pipe fitting may further comprise sensing means arranged to provide an electrical signal indicative of the force with which, in use, the fitting is gripping the pipe. This can be used to provide feedback to an installer to assist with correct fitting. The sensing means may for instance be provided as a sensor placed between said inner layer and said pipe or as at least a portion of the inner layer, the material of which is constituted to provide the electrical output.

A preferred form of adjustable fixing means for the fitting is a tapered wedge arrangement. Such an arrangement may include a fixing member which is arranged to engage edges of the semi-circular parts and to pull said edges closer together with movement in a direction generally parallel with the longitudinal axis of the pipe.

The invention additionally encompasses a system comprising such a pipe fitting and fixing apparatus arranged to apply a predetermined maximum force to the fixing member according to a desired gripping force to be applied by the fitting to the pipe. Preferably the fixing apparatus comprises means arranged to adjust said maximum force to be applied to said fixing member.

When using a fitting which provides an electrical output as mentioned above, the fixing apparatus may be responsive to said electrical signal to adjust said fixing means to cause said fitting to grip said pipe with a desired force.

The present invention thus permits a pipe fitting such as a ferrule strap to be fitted to a pipe with the grip of the fitting onto the pipe being tightened to a degree where the compression forces applied by the ferrule strap balance the forces created by the pressurization of the pipe during use whereby the material forming the walls of the pipe within the ferrule strap is under no significant tensile stress.

The present invention further provides a pipe fitting comprising a first part adapted to be fitted to a second part, and fixing means adapted to apply a force to fix said first and second parts together, and a sensor means arranged to be located between said first and second parts and to provide an electrical signal indicative of the force applied between said parts.

In this case it may that either the first and second parts are parts of the fitting, or the second part is at least a portion of a pipe or other element to which the fitting is to be fitted.

The sensor may be formed as part of a sealing or other resilient member of said fitting, and may for instance be of EPDM rubber.

The present invention will be better understood from the following description of preferred embodiments of the invention which is given by way of example only and with reference to the accompanying drawings, in which: Fig. 1 is a cross sectional view of a ferrule strap according to the preferred embodiment; Fig. 2 is a cut away perspective view of the embodiment shown in Fig. 1; Fig. 3 is a plan view of a wedge element forming part of the embodiment shown in Fig.l; Fig. 4 is a schematic view of the strap of Fig. 1 attached to a pipe and an associated tool used in a preferred system for fitting the strap; and Fig. 5 is a schematic sectional view through an exemplary pipe fitting according to the second embodiment.

In the first embodiment, a ferrule strap or similar pipe fitting is formed of two principal layers. An outer layer provides the strength required for the fitting, when strapped around a plastics pipe, to clamp adequately onto the pipe while being flexible to adapt to the shape of the pipe. This layer may be of stainless steel. An inner, rubber, layer distributes the clamping force across the exterior of the pipe.

In the second embodiment, a sensor is incorporated in a pipe fitting, which may or may not be according to the first embodiment, which gives an output indicative of the clamping force which has been applied.

Figs. 1 and 2 show respectively cross sectional and cut away perspective views of the ferrule strap according to the preferred embodiment indicated generally by the numeral 1 assembled around a pipe 2. The ferrule strap 1 carries a fitting 10, illustrated schematically in the drawings, which is arranged to be connected to a further length of pipe (not shown) so as to make a junction between the two pipes.

Fitting 10 is arranged in line with a hole 21 in pipe 2 so as to permit communication between the respective interiors of the two pipes. A preferred form for fitting 10 is the self tapping type, the details of which are well known, but the invention is equally applicable to other types of pipe fitting.

Ferrule strap 1 is made up of two major parts 11, 12 each of which is of a generally semi-circular cross-section such that, as can be seen in particular in Fig.1, they together surround most of the circumference of the pipe 2. Parts 11 and 12 are made of a high strength (modulus) material. This enables these parts to be strong enough in tension (around the hoop formed by the fitting) to bear the load of the compressive forces applied to the pipe, while being thin enough to adapt to the shape of the pipe which may, at any particular location, not be exactly round. A suitable material for this is a metal such as stainless steel.

The edges of parts 11 and 12 which extend axially along pipe 2 are bent over to form, in cross section hook portions 1 la, 1 lb, 12a, 12b respectively which enable parts 11 and 12 to be joined as described below.

Ferrule strap 1 further includes two parts 13, 14 which are referred to herein as wedges. The edges ofwedges 13, 14 are also bent over toformhook portions i3a, 13b, 14a, 14b respectively. To assemble the ferrule strap 1 around the pipe 2, the parts 11 and 12 are positioned around the pipe as shown and wedges 13, 14 are slid onto hook portions 11 a, 11 b, 12a, 12b in the axial direction of pipe 2 such that hook portions 13a, 13b, 14a, 14b engage therewith as shown.

Fig. 3 illustrates a plan view of wedge 13, being a top plan view, or a view looking from the exterior of the pipe fitting shown in Figs. 1 and 2. Along the edges of wedge 13 run respective hook portions 13a and 13b as described above. Pig. 3 further illustrates that wedge 13 is tapered from one end to the other. Typically the angle of the taper is 3.5 - 4 , an angle that is in engineering terms considered to be "self-locking". The extreme edges of hook portions lla and 12a are also arranged to be angled in relation to the axial direction of pipe 2 at the same angle.

Wedge 13 is assembled onto hook portions 1 la, 12a by sliding the wider end of wedge 13 over the narrower end of hook portions 1 la, 12a. It will be appreciated that, due to the tapering of the wedge and the corresponding hook portions, the further the wedge is pushed on the closer the hook portions 1 la and 12a are pulled.

Wedge 14 and hook portions 1 lb and 12b are arranged identically in the preferred embodiment, whereby the ferrule strap I can be tightened onto the pipe 2 by the adjustment of both of wedges 13 and 14. This provides a tightening mechanism which is symmetrical with regard to the pipe fitting 10 and therefore is suitable for minimising movement of pipe fitting 10 from its intended position during tightening.

However it may be the case that one of wedges 13 or 14 is provided with parallel edges and hooks such that all of the tightening adjustment is made by moving the other one of the wedges.

These wedges can be assembled in the field using a number of methods and/or tools. A preferred system and method of fitting is described later.

Finally, ferrule strap I includes an intermediate layer 15 which is located between the parts 11 and 12 and the exterior of pipe 2. Intermediate layer 15 is of a lower stiffness than the parts 11 and 12, and is shaped to correspond with the other parts of the ferrule strap. In the illustrated embodiment the intermediate layer is provided in two separate pieces, each fitting within one of the two major parts l l and 12. However it may be provided in any suitable form, for instance it may be provided as a single piece which extends around substantially all of the circumference of the pipe 2. It is provided with a hole at a location which corresponds with the location of the pipe fitting to and a sealing element around the hole. , The intermediate layer 15 has a number of functions. Firstly it provides the seal between,the strap 1 and the outer surface of the pipe 2, and it may be provided wills suitable shaping around the hole beneath the pipe fitting 10 to assist in providing the seal at that location.

Secondly, and significantly within this invention, it functions to apply and spread the compressive force active on the host pipe, caused by the tightening of the strap onto the pipe as described above, over a larger area than in the prior art. In particular it will be seen that the illustrated ferrule strap has a significant length in the axial direction of the pipe 2, whereby that length is greater than, and encompasses, the width of the pipe fitting 10. The strap therefore extends along the pipe from one portion of the pipe which is structurally substantially unaffected by the presence of the hole 21 to another.

The ferrule strap 1 itself is able to be tightened to a degree such that all of the forces caused by compression of the fluid carried in the pipe, which are borne by the pipe walls in a straight length of pipe, are instead at least substantially borne by the ferrule strap over the length of pipe enclosed within the strap. This means that the material forming the pipe wall around the hole 21 is substantially unstressed thereby significantly reducing the chances of failure by the formation of cracks in that material. In the prior art, that material tended to be either in compression resulting from over tightening of the strap or in tension resulting from under tightening. Also, prior art straps which were narrow compared to the size of fitting 10 did not enclose all of the material affected by the presence of the hole in the pipe wall.

Fig. 4 illustrates in schematic form, the assembly of strap 1 onto pipe 2 in a plan view and shows the fitting of wedge 13 onto edges 11 a, 12a as described above.

As will be apparent, the wedge 13 is fitted onto edges 1 la, 12a in the direction of arrow A, and further movement in the same direction causes strap 1 to tighten onto pipe 2.

Fig. 4 also illustrates schematically a tool which may be used in the fitting of the strap 1 to pipe 2. Essentially tool 3 comprises a pair of jaws 31, 32 which may be closed by manipulation of handles 35 by a user. In particular movable jaw 32 may be moved closer to fixed jaw 31 by use of handles 35. Movable jaw 32 is carried by arm 33 on rod 34. Preferably either the handle mechanism 35 or the mounting of arm 33 onto rod 34, or another part of the tool, includes a mechanism which acts to limit the maximum closing force which may be applied by jaws 31, 32.

In use, jaws 31, 32 are placed around the strap and wedge arrangement with, for instance, jaw 31 acting on edge l to of strap 1 and jaw 32 acting on edge 13c. The edges on which the jaws act may be specially formed to bear the applied load, or this may not be necessary, depending on the basic construction of the parts.

This fitting system can be used to fit the strap to the pipe so as to markedly reduce the chance of failure of the pipe at the strap location. As discussed above, either over-or under-tightening of the straps can cause failure of the pipe. Depending on the specification of the pipe to which the strap is to be fitted and its operating conditions (such as internal pressure, and temperature) it is possible to calculate the desired compression to be applied by the strap to the exterior of the pipe.

Because of possible variation in the exact size and shape of the primary pipe, this desired compression does not translate to an ideal position for wedge 13 on the strap. It does though translate to a desired force applied when fitting wedge 13 onto the strap. When fitting the strap therefore preferably tool 3 is set or selected such that the maximum force it can apply between the jaws is the desired fitting force.

The invention therefore provides an arrangement in which a simple yet easily adjustable tightening mechanism is provided whereby the clamping forces can be controlled, and the applied forces are distributed across the pipe enclosed in the strap.

lO Research has shown that failure to control clamping pressure is a cause of premature failure and leakage in pipe work, and so the present invention also extends to a system using a strap as described above which permits proper monitoring and installation of such a strap to improve its ongoing performance. In particular it is further proposed that not only a desired clamping pressure should be calculated on the basis of the operating condition of the strap, but also that the strap should incorporate means for indicating when such clamping pressure is achieved.

A basic requirement in such a system is to measure the interracial contact pressure between the ferrule strap 1 and pipe 2. This may be achieved by placing a sensor suitable for measuring such pressure between the pipe and the strap or such a sensor may be incorporated into the intermediate layer 15 of the strap described above. By way of example only, the intermediate layer may be wholly or partly made of a conductive polymer arranged to generate an output dependent upon pressure such that it functions as such a sensor. Alternatively a modified EPDM rubber gasket material could be formulated with proportional pressure/conductance characteristics. In either case the output resistance of the sensor varies with pressure and can be used via suitable electronics to control contact pressure during installation. This is schematically illustrated in Fig. 4 which shows wires 45 running from the sensor in the strap to electronics system 4.

A basic system may simply use the electrical response to indicate the clamping pressure such that the strap can be tightened to a desired degree. However, the introduction of sensor electronics also provides an opportunity to record and allow traceability or audit trailing of many parameters associated with the installation process.

In one possible system, the sensor electronics 4 are built into installation tooling or supplied as a separate ruggedized handheld unit. The unit incorporates a means of communication such as a bar code reader, some means of entering alphanumeric data and a means of printing and/or uploading data to a central database.

In such a system, a unique code, such as a bar code, is factory assigned to each ferrule strap and recorded in a database with information such as: À date of manufacture À strap diameter maximum pressure rating

À seal specification

À outlet size À pressure sensor calibration value Other data added to the database by the installer might include: À installer ID À service connection address (possibly GPS location) À target fitting pressure* À date and time of installation À host pipe details: À material À diameter À pressure rating À manufacturer À manufacturers production code À measured operating pressure at time of day Most importantly the actual fitting pressure applied during installation will be measured and logged.

*The target fitting pressure used during installation might be determined from: À the pressure rating of the pipe or the measured operating pressure of the main In operation, the recording of such data can be used to improve the performance of installed ferrule straps. The following description is of one proposed sequence conducted by an installer using a suitable data logger and installing a strap as described above.

Following excavation of a pipe to which a strap is to be fitted, the pipe is cleaned and any visible identification recorded. All the relevant data required is entered into the logger used by the installer. The bar code on the strap is swiped, the ferrule strap is loosely fitted to the pipe, and the logger is connected to the sensor built into the ferrule strap. The fitter tightens the strap until an audible alarm from the logger tells him to stop. This may be a variable spaced pulsed tone with the spacing shortening until a continuous pulse indicates when to stop. The logger is I S disconnected from the strap sensor blocking further data entry and all data may be printed or preferably transmitted via mobile phone link and automated email to a central collection point.

It will therefore be appreciated that the present invention provides a ferrule strap with improved performance as compared to prior art devices, and an improved

system for installation in the field.

In alternative embodiment the invention provides a system using a sensor as mentioned above incorporated into any of a number of types of pipe fitting in which two parts are clamped together with a force. The sensor may be inserted adjacent to or incorporated into a gasket used in a simple flange fitting for instance, as illustrated in Fig. 5.

Fig. 5 is a schematic sectional view of a flanged pipe 51 fitted to a representative member 55 by way of fitting bolts 52. Provided within the fitting is a gasket 53. As discussed above in relation to figure 4 it is desired to measure the interracial contact pressure in the fitting. This may be achieved by placing a sensor suitable for measuring such pressure adjacent to gasket 53 or such a sensor may be incorporated into the gasket 53. As noted above, to achieve this, the gasket 53 may be wholly or partly made of a conductive polymer arranged to generate an output dependent upon pressure such that it functions as such a sensor.

Alternatively a modified EPDM rubber gasket material could be formulated with proportional pressure/conductance characteristics. In either case the output resistance of the sensor varies with pressure and can be used via suitable electronics to control contact pressure during installation. This is schematically illustrated in Fig. 5 which shows wires 45 running from the sensor to electronics system 4.

The possible uses of this output are the same or similar to those outlined above in relation to Fig. 4. In particular, this arrangement enables the tightening of the fitting to be done to a required degree and also monitored. Additionally the further data mentioned above may also be logged in conjunction with the installation of the pipe fitting. This provides advantages in terms of monitoring and auditing which are not available with simple traditional fittings.

Claims

Claims: 1. A pipe fitting arranged to be fitted to a primary pipe, the

fitting comprising two substantially semi-circular parts adapted to be arranged together to fit around the primary pipe and fixing means arranged to fix the respective edges of the semi- circular parts together to cause the fitting to grip the pipe, said semi- circular parts being formed of an outer layer of a first material and which is adapted to flex whereby to adapt to the cross-sectional shape of the primary pipe while carrying the stress necessary for the fitting to grip the pipe, and an inner layer of a second material arranged to contact the external surface of the pipe, in use, and to distribute the force applied by said outer layer across the surface of said pipe.
2. A pipe fitting according to claim 1 comprising a branch fitting in one of said semi-circular parts arranged to cooperate, in use, with a hole of a predetermined size in said primary pipe to provide a branch therefrom.
3. A pipe fitting according to claim 2 in which a portion of said inner layer is shaped to provide a seal around said hole.
4. A pipe fitting according to claim 1, 2 or 3, in which said first material has a higher stiffness or modulus than said second material.
5. A pipe fitting according to claim 4 in which said first material is stainless steel.
6. A pipe fitting according to claim 4 or 5 in which said second material is EPDM rubber.
7. A pipe fitting according to any of claims 1-6 in which said fixing means is adjustable whereby the force with which the fitting, in use, grips the pipe is selectable or adjustable.
8. A pipe fitting according to claim 7 comprising sensing means arranged to provide an electrical signal indicative of the force with which, in use, the fitting is gripping the pipe.
9. A pipe fitting according to claim 8 in which said sensing means comprises a sensor placed between said inner layer and said pipe.
10. A pipe fitting according to claim 8 in which said sensing means comprises at least a portion of said inner layer, the material of which is constituted to provide said electrical output.
1 1. A pipe fitting according to any of claims 7-10 in which at least one of said fixing means comprises a tapered wedge arrangement.
1 2. A pipe fitting according to claim 11 in which said tapered wedge arrangement comprises a fixing member which is arranged to engage edges of said semi-circular parts and to pull said edges closer together with movement in a direction generally parallel with the longitudinal axis of the pipe.
13. A system comprising a pipe fitting according to claim 12 and fixing apparatus arranged to apply a predetermined maximum force to said fixing member according to a desired gripping force to be applied by said fitting to said pipe.
14. A system according to claim 13 in which said fixing apparatus comprising means arranged to adjust said maximum force to be applied to said fixing member.
15. A system comprising a pipe fitting according to any of claims 8-10 and fixing apparatus responsive to said electrical signal to adjust said fixing means to cause said fitting to grip said pipe with a desired force.
16. A pipe fitting comprising a first part adapted to be fitted to a second part, and fixing means adapted to apply a force to fix said first and second parts together, and a sensor means arranged to be located between said first and second parts and to provide an electrical signal indicative of the force applied between said parts.
17. A pipe fitting according to claim 17 in which said first and second parts are parts of the fitting.
lS 18. A pipe fitting according to claim 17 in which said second part is at least a portion of a pipe or other element to which the fitting is to be fitted.
19. A pipe fitting according to claim 16, 17 or 18 in which said sensor is formed as part of a sealing or other resilient member of said fitting.
20. A pipe fitting according to claim 19 in which said sealing or other member is of EPDM rubber.