COUPLING

The present invention relates to a coupling for connecting tubular conduits, in particular for connecting lengths of pipe as part of a fluid transport system.

Fluid transport systems are known for conveying materials, such as liquids and gasses, with common examples including fuels such as gas and oil. The systems may vary from domestic plumbing systems installed in a building for conveying water to oil and gas pipelines for conveying fuel over thousands of miles. The tubular conduits used in fluid transport of fuel may be made of different metals, including steel, iron, copper, aluminium and plastic.

For smaller diameter pipes, push fit couplings can be used, for example as described in GB2,378,992. However, for pipe diameters above around 5cms, the force required to push the end of a pipe into such a push fit coupling becomes too high for manual connection. In addition, pipes connected by push fit couplings are able to rotate relative to each other, which can cause valve taps to move out of an optimum position.

For larger diameter pipes, welded joints can be used. However, welded joints have the disadvantage of requiring skilled workers as well as having negative health and safety and environmental implications. For example, construction of a gas conveying pipeline made from 40 metre long lengths of steel pipe, and with a 1 metre diameter, conventionally use welded joints. Each joint can take a skilled team a whole day to make, when taking into consideration, the

deployment of equipment at the joint location and inspection of the joint by X- ray equipment. Also, around 1 in 10 of such welded joints will have to be repaired after such an inspection. This makes pipelines expensive and time consuming to construct.

Where plastic pipes are used, heat fused joints may be used, in which the ends of the pipes to be connected are heated up and then fused together.

Push fit couplings, welded joints and fused joints are difficult to disconnect, for example for repair or maintenance, with such disconnection often causing damage to the pipes.

Various attempts have been made to construct pipe couplings including radially extending fixing elements, for example, US4,288,114, which describes a coupling in which fixing elements pass through the coupling and engage pre-drilled holes in a pipe end. One problem with such fixing elements is that they tend to shear when a force acts between the coupling and the pipe, in a direction parallel to the longitudinal axis of the pipe. Such forces are created, for example, where the coupling comprises a valve. Then when the valve is closed, the weight of fluid in the pipe, upstream of the valve, has to be supported by the connection between the valve and the pipe. This can generate significant forces between the coupling and the pipe, in a direction parallel to the longitudinal axis of the pipe.

A first aspect of the present invention aims to overcome at least some of the problems set out above by providing a coupling having at least one coupling end for connection to a tubular conduit, wherein each coupling end comprises: a housing defining a tubular wall of a receiving recess for receiving an end of such a tubular conduit, the housing comprising a plurality of through holes, formed with an outer internally threaded portion and an inner portion, and extending from an external surface of the housing through to the tubular wall of the receiving recess; and a plurality of fixing elements, corresponding to the plurality of through holes, wherein each fixing element comprises: an outer portion formed with an external screw thread engageable with the internally threaded portion of the corresponding though holes; and an inner tapered portion tapering from a wider end closer to the outer portion to a narrower end, the tapered surface for face to face engagement with sidewalls of a correspondingly tapered bore formed in an external surface of such a tubular conduit.

The coupling may be designed so that movement of the fixing elements into the corresponding though holes in the coupling end housing is limited by the tapered surface of the inner portion of each fixing element engaging the tapered surface of the corresponding bore.

A coupling end according to the present invention may ensure a face to face engagement between a tapered face of each fixing element and a correspondingly tapered face of the corresponding bore in the tubular conduit, for example around 360°, which helps to prevent the fixing element from

shearing due to longitudinal forces acting between the coupling and a tubular conduit fitted within it. To this end it is preferred that the tapered face of the fixing element is not threaded and is preferably smooth. It is also preferred that the tapered face of a corresponding bore in such a tubular conduit is also not threaded and is preferably smooth.

Each fixing element may also comprise an intermediate portion, located between the outer threaded portion and the inner tapered portion, carrying a first annular seal for engaging a part of the inner portion of the corresponding through hole so as to form a fluid tight seal between the fixing element and the through hole. The internal surface of the inner portion of each through hole is preferably not threaded and is preferably smooth. The seal on the intermediate portion of the fixing element ensures a fluid tight seal between each fixing element and the coupling end.

The coupling end design ensures a face to face engagement and sealing, around 360°, which is effective for tolerance variations, in particular, in the thickness and the shape of the tubular conduit end.

The coupling may additionally comprise an abutment surface extending inwardly of the tubular wall for abutting an end of a tubular conduit; and a second annular seal for making a fluid tight seal against an external surface of the tubular conduit. In this case the second seal may be located at a position between the fixing elements and an open end of the receiving recess. Such an arrangement provides an accurate positioning of the tubular conduit within

the coupling end, in particular prior to or during drilling of the tapered bores in the end of the tubular conduit, if they are drilled with the tubular conduit positioned within the coupling end. The second seal may be an annular seal mounted within an annular recess formed in the tubular wall of the receiving recess. The abutment may be an annular shoulder extending from the tubular wall into the receiving recess or may be an end face of the coupling end. In one arrangement, the second seal may be adjacent to an open end of the receiving recess, the abutment may be remote from the open end of the receiving recess and the fixing elements may be located between the second seal and the abutment.

Generally, the tubular conduit will be a right cylindrical pipe, in which case, the tubular wall of the receiving recess may have the shape of a right cylinder. The tubular wall may have a longitudinal axis of symmetry and the or each fixing element and through hole may be concentric with a line extending and a direction substantially radially of the longitudinal axis. While is a preferred embodiment the fixing elements extend substantially radially, they may be angled to the radius, for example up to 45°.

The coupling may comprise two or more coupling ends and a conduit between the coupling ends. The conduit between the coupling ends may comprise a valve or a junction or other such element which may be commonly found in pipe couplings.

The intermediate portion of each fixing element may comprise an annular recess within which is located the first annular seal. In this way the first annular seal is able to provide a seal between the intermediate portion of the fixing element and the coupling housing. Adequate sealing is ensured even if the fixing element is fitted into a corresponding through hole in the coupling end housing with the annular seal located to a different depth within the through hole. The depth at which the first seal is located may vary due to tolerance variations in the size and shape of the tubular conduit in order to ensure face to face contact between the tapered inner portion of the fixing element and the corresponding tapered bore in the end of the tubular conduit.

The tapered surface of the inner portion of the fixing element and the corresponding tapered portion in the bore in the tubular conduit may be substantially frusto-conical. This prevents shearing of the fixing elements regardless of the final rotational position of the fixing elements within the corresponding through holes and bores. In addition, it simplifies the drilling of the corresponding tapered bore in the tubular conduit end and ensures face to face engagement of the tapered surfaces of the fixing elements and corresponding bores around 360° regardless of the final position of the fixing element. The tapered surfaces may taper at an angle to the longitudinal axis of the coupling end of between 10° and 60°, more preferably between 20° and 40° and more preferably around 30°.

The fixing elements may additionally comprise a fourth substantially cylindrical portion, located inwardly of the tapered portion, having a diameter less than or

equal to the minimum diameter of the tapered portion. The tapered and fourth portions may extend through such a corresponding through bore formed through such a tubular conduit, with the tapered portion in face to face engagement with the tapered portion of the bore and the fourth portion extending through the remainder of the bore to the internal surface of the tubular conduit.

Each through hole may have a radially inner end of the inner portion adjacent to the tubular wall of the receiving recess which tapers from a first diameter to a second smaller diameter at the tubular wall. Correspondingly, the tapered inner portion of each fixing element may match the tapered portion of the through hole. Then with a tubular conduit end fitted into the receiving recess, the tapered inner end of the fixing element extends from the tapered inner end of the through hole into a correspondingly tapered bore formed within the tubular conduit end so as to provide a strong shear resistant fixing between the tubular conduit and the coupling. The length of the tapered inner portion of each through hole may be less than 50%, in particular less than 33% of the entire length of the through hole.

The inner tapered end of each fixing element may be dimensioned to pass through the correspondingly tapered bore in the tubular conduit through to the inwardly facing surface of such a tubular conduit.

The coupling end may be an end cap comprising the tubular wall terminated by an end wall, which end wall may form the abutment surface. End caps in

fluid transport systems are often subjected to high strain and so the tapered fixing elements and correspondingly tapered through hole are particularly useful where the coupling end is an end cap. The portion of each fixing element, radially outwardly of the tapered inner portion, may be untapered.

There is also provided a coupling assembly comprising the coupling as described above with a tubular conduit fitted thereto, in which the inner portion of each fixing element is in face to face engagement with the sidewalls of a correspondingly tapered bore portion formed into an external surface of the tubular conduit. As described above this face to face engagement helps to prevent shearing of the fixing elements. An end of the tubular conduit may abut the abutment surface and the second annular seal may make a fluid tight seal against an external surface of the tubular conduit. The fourth portion or the inner tapered portion of the fixing elements may extend right through to an internal surface of the tubular conduit.

There is also provided a fixing element, which may be suitable for use in the coupling described above, in which the fixing element comprises: an outer portion formed with an external screw thread; an intermediate portion, inwardly of the outer portion, carrying a first annular seal; and a inner tapered portion, inwardly of the intermediate portion and tapering from a wider end adjacent the intermediate portion to a narrower end. The intermediate portion of the fixing element may comprise an annular recess within which is located the first annular seal. The intermediate portion and or the inner portion of the fixing element preferably have an unthreaded surface, preferably a smooth

surface. The tapered surface of the inner portion of the fixing may be substantially frusto-conical. In addition, the fixing element may also include a fourth portion , which may be substantially cylindrical and which may be located inwardly of the inner portion and which may have a diameter less than or equal to the minimum diameter of the tapered inner portion.

There is also provided a method of fixing a tubular conduit in a coupling of the type described above, comprising the steps of: fitting an end of the tubular conduit within the receiving recess of the coupling, drilling a first tapered bore in the tubular conduit by directing a drilling tool through one of the through holes in the coupling end housing; and fixing one of the fixing elements through the through hole in the coupling end to engage the first bore in the tubular conduit. The method of fitment is relatively quick and simple. It ensures that the bores in the end of the tubular conduit are correctly positioned. The coupling end housing may be provided with a plurality of guide bosses, which extend radially outwardly of each through hole in order to guide a drilling tool, fitted with a suitable shaped drilling bit. The guide bosses, may act to guide the drilling tool to drill a bore within the end of the tubular conduit, which bore is aligned with the corresponding through hole in the coupling. The guide bosses may also include a stop surface for limiting the depth to which the bore in the end of the tubular conduit is drilled. The drilling and fixing steps may then be repeated for each fixing element. The tapered bores in the tubular conduit end may be drilled partially through a wall of the tubular conduit or they may be drilled completely through a wall of a tubular conduit.

The invention will now be described by way of example only and with reference to the accompanying schematic drawings, wherein:

Figure 1 shows a partial longitudinal cross-section through one end of a coupling according to the present invention with an end of a pipe length connected to the coupling;

Figure 2 shows a plan view of a coupling according to the present invention;

Figure 3 shows a side on view of a coupling, incorporating a valve, according to the present invention;

Figure 4 shows a cross-sectional view through a tapered bore in a pipe end, according to the present invention;

Figure 5 shows a partial longitudinal cross-section through a coupling according to the present invention with an end of a pipe length connected to the coupling;

Figure 6 shows the profile of a drilling tool and a forward part of a chuck in which the drilling tool is fixed, suitable for making bores in pipe ends to be fitted into a coupling of the present invention;

Figure 7 shows a longitudinal cross-section through a pipe coupling according to the present invention in the form of an end cap into which an end of a pipe is fitted; and

Figure 8 shows a longitudinal cross-section through a fixing element of the coupling of Figure 7.

Figures 2 and 3 and 7 show couplings (1a, 1b, 1c) according to the present invention, each comprising at least one coupling end (2) of the type shown in

Figures 1 , 5 and 7. A length Qf tubular conduit or pipe (4) is shown connected to the or each coupling end (2) of each of the couplings (1 a, 1 b, 1 c). A central portion (3) of the couplings (1a, 1 b) may comprise a simple conduit connecting the ends of the pipes (4) or may comprise a valve, junction or connection to another section of pipe. The coupling (1c) of Figure 7 comprises an end cap.

A first embodiment of each coupling end is shown in cross-section in Figure 1 and has an end of a length of tubular conduit or pipe (4) connected to it. The coupling end comprises a housing (2) defining a tubular wall (14) of a receiving recess for receiving an end of the pipe (4). The coupling end is tubular and in Figure 1 is shown as a cylinder with a circular cross-section at its inwardly (14) and outwardly (16) facing surfaces. An annular abutment (6) extends radially inwardly from inwardly facing surface or tubular wall (14) of the coupling end, at a set distance Di from an open end (8) of the coupling end (2). An annular recess (10) is formed in the inwardly facing surface of the tubular wall (14) of the coupling end (2) for housing a second annular seal (12), at a set distance D ₂ from the open end (8) of the receiving recess of the coupling end.

A plurality of through holes (18) are formed through the housing of the coupling end (2) from the external surface (16) to the tubular wall (14) of the coupling end. The bore of each through hole (18) is substantially concentric with a line (20) extending substantially radially from the longitudinal axis (21 ) of the coupling end (2). It is not essential that the through holes (18) extend

radially, as they may extend at an angle to the radius. In the example shown in Figure 1 , six such though holes (18) are formed in the coupling end (2), each a distance D ₃ from the open end (8) of the coupling end. Distance D ₃ is greater than distance D ₂ and is less than distance Di. Each through hole (18) has an outer threaded portion (18a) adjacent the outwardly facing surface (16) of the coupling end (2) and an inner portion (18b), which is not threaded, adjacent the inwardly facing face (14) of the coupling end. The inner portion (18b) has a smaller diameter than the outer portion (18a). Thus, a step is created between the outer threaded portion (18a) and the inner portion (18b). A fixing element (24) is fixed within each through hole (18) and passes through each through hole to engage a corresponding bore, which tapers outwardly at its radially outer end, in the wall of the pipe (4) fitted within the coupling end (2), as is described below.

The fixing element (24) comprises a head (26), with a slot (28) formed in the top of the head, suitable for engagement with a screwing tool, such as a screwing tool suitable for fitment in and driving by a power tool, such as a drilling and/or driving power tool. Accordingly, the slot (28) can be suitable shaped (See Figure 2) to provide good engagement with the type of screwing tools known in the art. Adjacent the head (26) of the fixing element (24), is a first outer portion (24a) of the fixing element, which is externally threaded so as to engage the internally threaded outer portion (18a) of the through holes (18) of the coupling end (2). The fixing element (24) also comprises a second intermediate portion (24b) of reduced diameter as compared to the outer portion (24a), sized to smoothly fit within the inner portion (18b) of the through

hole (18). The fixing element (24), when fitted within the through hole (18) extends radially inwardly of the inwardly facing surface (14) of the coupling end (2). The fixing element has a third inner portion (24c) radially inwardly of the second intermediate portion (24b), which tapers from the larger diameter of the intermediate portion (24b) to a smaller diameter of a fourth portion (24d). The fourth portion (24d) is located at the radially inner end of the third inner portion (24c). Preferably, the tapered third portion (24c) is frusto- conical. An annular groove is formed around the second intermediate portion (24b) of the fixing element (24), preferably with the groove adjacent to the first outer portion (24a). A first annular seal (22) is located within the annular groove.

To fix a pipe (4) within a coupling end (2), first the fixing elements (24) are removed from the coupling end (2) and the pipe (4) is slideably mounted within the coupling end, until the end face of the pipe abuts the annular abutment (6). The tubular wall (14) of the coupling end (2) is sized so that it fits smoothly around the external surface of the pipe end (4).

Then with the pipe in place, a bore (30) of a suitable size to fit the tapered portion (24c) and the fourth portion (24d) of the fixing element (24) is drilled or machined through the wall of the pipe end (4) by passing a suitably shaped drill bit (32), as shown in Figure 6, of a drilling tool through one of the through holes (18) in the coupling end (2). In this way, the bore (30) in the pipe (4) is aligned with a corresponding one of the through holes in the coupling end. A tapered bore (30) is made corresponding to each of the through holes (18) in

the coupling end (2), by passing the drilling tool through each of the through holes in turn. A guide is provided between the drilling tool and the body of the coupling end (2), in order to ensure that the drill bit (32) is positioned to drill a bore (30) in the pipe, which bore is symmetric about the axis (20) of the through hole (18) and which makes a bore with the tapered portion extending to a predetermined depth within the wall of the end of the pipe (4). Accordingly, as shown in Figure 4, the bore (30) in the pipe (4) has a radially inner section with a diameter matching the diameter of the fourth portion (24d) of the fixing element (24) and a radially outer tapered portion which tapers to a larger diameter towards the outer surface of the pipe. The taper of the bore in the pipe (4) is drilled to match the taper of the third inner portion (24c) of the fixing element (24).

Then one of the fixing elements (24) is fitted within one of the through holes (18) so that the fixing element passes through the through hole (18) and its inner portions (24c, 24d) passes into the corresponding bore (30) of the pipe (4). The fixing element (24) is screwed into position by engaging the internal thread of the outer portion (18a) of the through hole (18) with the external thread of the first outer portion (24a) of the fixing element (24) and rotating the fixing element until the tapered surface of the fixing element inner third portion (24c) abuts the mating taper of the bore (30) in the pipe (4), as is shown in Figure 1.

It is important that the fixing elements (24), coupling through holes (18) and the bores (30) in the pipe end (4) are shaped so that the forward movement of

each fixing element into the bore in the pipe is limited by the engagement of the tapered surface of the inner third portion (24c) of the fixing element with the corresponding tapered surface of the bore in the pipe end.

Referring to the fixing element (24) in the upper half of Figure 1 , the fixing element is screwed into the through hole (18) and the bore (30) in the pipe (4) until the tapered surfaces of the fixing element and the bore engage. The first annular seal (22) forms a fluid tight seal between the intermediate portion (24b) of the fixing element and the inner portion (18b) of the through hole (18). The step between the outer (24a) and intermediate (24b) portions of the fixing element abuts the corresponding step between the outer (18a) and inner (18b) portions of the through hole (18).

Now referring to the fixing element (24) in the lower half of Figure 1 , the fixing element is screwed into the through hole (18) and the bore (30) in the pipe (4) until the tapered surfaces of the fixing element and the bore engage. However, as the engagement of the tapered surfaces of the fixing element (24) and the bore (30) in the pipe (4) limit the forward movement of the fixing element into the through hole (18), there is small gap between the step between the outer (24a) and intermediate (24b) portions of the fixing element and the corresponding step between the outer (18a) and inner (18b) portions of the through hole. Nevertheless, the annular seal (22) forms a fluid tight seal between the intermediate portion (24b) of the fixing element (24) and the inner portion (18b) of the through hole (18). In this way, the fixing element

(24) is designed to take into account small variations in the dimensions of the end of the pipe and of the coupling end (2).

Figure 4 shows a cross-sectional view through a pipe end (4) wall, showing the shape of the bores (30) in the pipe end. As indicated above, it is preferred that the tapered section of the bore (30) is frusto-conical. The angle α of the taper is preferably between 10° and 60°, more preferably between 20° and 40° and more preferably around 30°.

The tapered abutting faces of the bores (30) in the pipe ends (4) and the inner third portion (24c) of the fixing element distributes forces acting longitudinally (substantially in the direction of the longitudinal axis (21 ) of the pipe (4)) and so helps to prevent shearing of the fixing element (24)at the interface between the internal surface (14) of the coupling end (2) and the external surface of the pipe (4). Significant longitudinal forces can be generated, for example, in the type of pipe joint shown in Figures 3 and 7, where a substantial weight of fluid is held in the pipe system above the pipe joint, for example, above the upwardly extending pipe in Figure 3. In the example of Figure 3, while the valve (3) is open, fluid is free to flow, under the action of gravity, down the upwardly extending pipe, change direction through 90° in the pipe coupling (1b) and then flow away from the coupling along the horizontally extending pipe. However, on closure of the valve (3), the connection between the pipe coupling (1b) and the upwardly extending pipe, all of a sudden, has to support the weight of water in the pipe system above the upwardly extending pipe. This leads to a sudden increase in the longitudinal forces acting between the

coupling (1b) and the upwardly extending pipe (4). Shearing of the fixing elements (24) is prevented by the tapered shape of the fixing element and the face to face engagement of the tapered section (24c) of the fixing element and the tapered section of the bore (30) in the pipe end (4) around 360°.

The pipe (4) is thus connected to the coupling end (2) and secured there against rotation. The drilling of the bores (30) and fitting of the fixing elements (30) procedure is then repeated for each of the fixing elements (24) and corresponding through holes (18), until all of the tapered portions (24c) of the fixing elements (24) engage corresponding bores (30) drilled within the pipe end (4), as shown in Figure 1.

Pipelines tend to vibrate, and such vibration can cause the fixing elements (24) to come loose. To avoid this, a connector can be fitted between the head (26) of the fixing element (24) and the outwardly facing surface (16) of the coupling end (2) so as to hold the fixing element (24) against rotation.

The couplings (1a, 1 b, 1c) according to the present invention with coupling ends (2) as described herein, are simple and easy to fit to a pipe (4), without requiring a skilled workforce of welders and only a simple drilling tool. The couplings (1a, 1b, 1c) are relatively cheap to make and are much simpler to install, especially where the pipes (4) are part of a pipeline of large diameter, for example, for transporting gas or oil. The couplings (1a, 1 b, 1c) are safe to fit, as they do not require welding. Cold drilling, cooled by running water, can be used to drill the bores (30) in the pipe (4), so as to prevent the generation

of sparks. The first and second seals (22, 12) provide a good seal between the coupling end (2) and the pipe (4) fitted within it and so is not susceptible to leaks. The pipes (4) fitted within the couplings (1a, 1b, 1c) are secured against rotation. Also, the fitting of the coupling end (2) to the pipe (4) does not obstruct the flow of fluid within the pipe. In addition, the pipes (4) can be removed from the couplings (1a, 1b, 1c), by simple removal of the fixing elements (24), for maintenance or repair purposes.

A second example of a pipe coupling according to the present invention is shown in Figure 5. Figure 5 shows a longitudinal cross-section similar to that shown in Figure 1 , in which the pipe coupling (1c) comprises a pipe end cap, which may optionally include a valve and/or a connection to another section of pipe. An end of a pipe (4) is fitted within the coupling end (2) of the pipe coupling (1c).

The coupling end (2) of Figure 5 is similar to that of figure 1 , with like parts identified by like numerals. Differences between the embodiments of Figures 1 and 5 are set out below. In Figure 5, the annular abutment is formed by the end surface (36) of the coupling (1c). In Figure 5, outwardly directed cylindrical bosses (38), extend radially (with respect to the longitudinal axis (21 ) of the coupling end (2)) outwardly of the remainder of the body of the coupling end so as to extend the through holes (18) outwardly, as compared to the through holes (18) of Figure 1. The through holes (18) of the embodiment of Figure 5 are not stepped as in Figure 1 , instead the radially (with respect to the longitudinal axis (20) of the bosses (38)) innermost part of

the internal thread on the outer portion (18a) of the through holes (18) has the same internal diameter as the inner portion (18b) of the through holes. The radially (with respect to the longitudinal axis (20) of the fixing elements (24)) innermost part of the external thread on the outer portion (24a) of the fixing elements (24) has the same diameter as the diameter of the intermediate portion (24b) of the fixing elements. In addition the annular recess in the intermediate portion (24b) of the fixing elements (24), which contains the first annular seal (22) is spaced slightly from the outer externally threaded portion (24a) of the fixing elements.

A drill bit (34) of the type shown in Figure 6 is fitted into a chuck (34) of a drilling or machining tool, so that the drill bit extends a predetermined distance forwardly of a forward end face (41) of the chuck (34). The drill bit (32) is rotatingly driven by the drilling tool via the chuck (34). The drill bit (32) is formed with a rearward non-cutting section (32a) with an external diameter matching the internal diameter of the inner portion (18b) of the through holes (18) shown in Figure 5. In this way the drill bit (32) is smoothly guided within the bosses (38) to ensure that the bores (30) drilled in the pipe end (4) are concentric with the longitudinal axis (20) of the through hole (18). The drill bit (32) has a forward cutting end, behind which is a cutting portion (32c) designed to cut the inner cylindrical portion (30b) of the bore (30) in the pipe end (4), to the precise diameter to receive the fourth portion (24d) of the fixing element (24). The drill bit (32) has a central cutting portion (32b), which is tapered so as to cut the outer tapered portion (30a) of the bore (30) in the pipe end (4), to the precise dimensions so as to receive, with face to face

engagement, the tapered portion (24c) of the fixing element (24). The drill bit (32) can advance forwardly within the through holes (18) cutting through the pipe end (4) to form the bores (30) until the forward face (41 ) of the chuck (34) abuts the outer end face (40) of the bosses (38). This ensures that the tapered portion (30a) of the bore (30) in the pipe end (4) is drilled to the correct depth within the pipe end.

Like parts are represented by like numerals, as in Figures 1 to 6, in each of the Figures 7 and 8.

Figure 7 shows an end of a pipe length (4) fitted within a coupling end (2) of a pipe coupling (1c) according to the present invention. In the example of Figure 7, the pipe coupling (1c) is in the form of a high pressure end cap assembly suitable for use in a valve arrangement, pump arrangement, boiler arrangement or as a pipe fitting termination. Alternatively, the pipe coupling may have more than one coupling end (2) connected by a conduit so as to couple two lengths of pipe. In this case, the conduit between the coupling ends of the pipe coupling may additionally comprise a valve or a connection to another section of pipe.

The coupling end (2) of Figure 7 is formed as a housing with a tubular wall (14) defining a receiving recess for receiving the pipe end (4). For example, in Figure 7, the housing has a substantially cylindrical outwardly facing surface (16) with a substantially circular cross-section and it has a substantially cylindrical inwardly facing surface (14) with a substantially circular cross-

section. The coupling end (2) also comprises an end wall (36) which terminates the receiving recess at one end of the tubular wall.

An annular recess (10) is formed in the inwardly facing surface (14) of the tubular wall of the coupling end (2) for housing a second annular seal (12). The second annular seal forms a seal between the outwardly facing surface of the pipe end (4) and the inwardly facing face (14) of the tubular wall. The coupling end (2) and the pipe end (4) are dimensioned so that the pipe end (4) slideably fits within the receiving recess of the coupling end with tight tolerances.

A plurality of through holes (18) is formed through the housing from the outwardly facing surface (16) to the inwardly facing surface (14). The bore of each through hole is substantially concentric with a line (20) extending substantially radially of the longitudinal axis (21 ) of the tubular wall. In the example shown in Figure 7 between two and eight through holes (18) are formed in the coupling end (2). It should be noted that the distance between the through holes (18) and an open end face (8) of the coupling end (2) is greater than the distance between the second annular seal (10) and the open end face.

Each through hole (18) has a radially outer threaded portion (18a) (radial with respect to the longitudinal axis (21) of the coupling end (2)) adjacent the outwardly facing surface (16) of the tubular wall and an inner portion (18b) comprising a central portion (19a) which is not threaded and a radially inner

tapered inner portion (19b) adjacent the inwardly facing surface (14) of the tubular wall. The tapered portion (19b) tapers from a wider part (first diameter (D)) adjacent the central portion (19a) to a narrower part (second smaller diameter (d)) adjacent the inwardly facing surface (14) of the tubular wall. Each through hole (18) has a length (L) in a radial direction (20) and the tapered portion (19b) has a length (/) in the radial direction which is less than 50% and preferably less than 33% of the length (L).

A fixing element or screw (24), which is also shown in Figure 8, is fixed within each through hole (18) and passes through each through hole to engage a bore (30) in the pipe end (4), as is described below. Each screw (24) has a radially outer externally threaded portion (24a) (radially with respect to the longitudinal axis (21 ) of the coupling end (6) when the fixing element is fitted within a through hole as shown in Figure 7) matching the dimensions of the internally threaded portions (18a) of the through holes (18), an intermediate portion (24b) matching the dimensions of the central portions (19a) of the through holes (18) and an inner tapered portion (24c) matching the dimensions of the tapered portions (19b) of the through holes (18). The inner tapered portion (24c) tapers continuously to an end face making the tapered inner portion of the screw frusto-conically shaped. When one of the screws (24) is fitted within a corresponding through hole (18), as is shown in Figure 7, part of the tapered inner portion (24c), extends radially inwardly of the through hole to engage a correspondingly tapered bore (30) formed in the pipe end (4). The intermediate portion (24b) of the screw (24) is formed with an annular recess (35) for receiving a first annular sealing ring (22). When the

screws (24) are fitted within the through holes (18), the annular sealing ring (22) of each screw seals between the screw and the adjacent central portion (19a) of the through hole (18). The screw (24) has an outer end surface (26) formed with a slot (28) suitable for engagement by a screwing tool, as is described above in relation to Figures 1 and 5.

To fix a pipe (4) within the coupling end (2) the screws (24) are removed from the coupling end (2) and the pipe end (4) is slideably mounted within the coupling end (2), until the pipe end abuts the end wall (36) forming the annular abutment. With the pipe end (4) in place a set of tapered bores (30), suitably tapered to receive the inner tapered end (24c) of each screw (24) is drilled through the pipe end (4) by passing a suitably shaped drilling bit of a drilling tool through each of the through holes (18) in turn and drilling through the pipe end (2) to form the tapered bores (30), as is described above in relation to Figures 1 and 5. In this way the bores (30) in the pipe end (4) are aligned with the through holes (18) in the coupling end (2). Then a screw (24) is passed into each of the through holes (18) and screwed therein to mate the internal thread of the outer portion (18a) of the through holes (18) with the external thread of the outer portion (24a) of the screws (24). Thus, the inner tapered ends (24c) of the screws (24) pass beyond the through holes (18) and into the tapered holes (30) of the pipe end (4), as is shown in Figure 7. Alternatively, the tapered holes (30) in the pipe end (4) may be formed prior to fitting of the pipe end into the coupling (1c).