PIPE JOINT, PARTICULARLY FOR LIGHT WEIGHT POLYETHYLENE PIPES

The invention relates to a pipe joint comprising a tubular pipe union for the end of a pipe to be fitted thereon, which union has an intermediate cylindrical section with a conical widening portion at the end designed to be fitted into the pipe and an abutment member at the opposite end, such as a radial shoulder or the like, acting as a limit stop for the pipe on said union, a nut being provided for locking the pipe on the union, which nut has a conical inner surface, which conical surface widens towards the fitting end of the union, i.e. the conical end of the union, whereas , at least over an area of shorter internal diameter, said nut has an internal diameter that is equal to or slightly smaller than the external diameter of the pipe to such an extent as to provide preliminary elastic engagement between the pipe and the nut when the latter is in the joint opening position, i.e. over the cylindrical section of the union and/or in the retracted position of abutment against the radial shoulder acting as a limit stop for the pipe, the pipe being clamped between the inner conical surface of the nut (3) and the outer conical surface at the end of the union by axial displacement of the nut towards the conical widening portion at the end of the union. Pipes of this type are well known in the art. Prior art joints are also formed of a body in the form of a union, and a nut. Prior art joints have the same operation and assembly characteristics as described

above . The pipe is fitted to abutment against an annular stop shoulder . When the pipe reaches its limit stop position it is elastically forced into the nut, which acts as a locking ring or between the cylindrical part of the union and said ring . Thus , the ring becomes integral with the pipe . By pulling the pipe in the pull-out direction" relative to the union, the clearance between the inner conical surface of the nut and the conical surface of the body progressively decreases until the pipe is clamped.

Among prior art joints, a particular joint has three axial tabs which extend the peripheral or skirt wall of the nut on the smaller diameter side, which tabs are 120° from each other. These tabs have three teeth at their ends , which serve two functions . The first function is not to allow the nut to be released from the union of the joint and the second function is to hold the pipe still during pipe mounting operations . In this case , the tabs have no effect on pipe clamping . However, connectors are clamped, like in the other prior art joints, by the conical surfaces of the nut and the union .

Particularly, these types of joints as well as the joints of the present invention are particularly suitable for PE pipes and especially for driplines that require simple and quick installation without using of equipment or tools .

Joints of this type can be joined together to form a joint for connection of two lengths of pipe or three or more lengths of pipe. Is in the former case, two unions and associated nuts are fixed in opposed, possibly coaxial positions, to form a single tubular union having conical widening surfaces at the two

opposite facing ends, a radial shoulder, particularly of annular shape, being provided in an intermediate area of a cylindrical section, to act as a stop abutment for the ends of the two lengths of pipe over the corresponding pipe union, whereas a nut is associated to each of the two unions respectively. When three unions are used to join together three lengths of pipe, such unions may be connected to form a T or Y shape, with an annular or radial stop abutment for the pipe being provided for each union. When even more unions are provided, these are interconnected to form a cross or star shape. The joint may obviously have one or more unions for connection to an end of a pipe, which communicate with one or more connection terminals of the type having threads or a glue and/or weld socket or a flange for connection to another correspondingly threaded, flanged or weld or glue socket-shaped terminal .

Prior art unions suffer from the drawback that, once that the connector has been mounted to the pipe, any displacement of the nut, caused by shocks or stresses that do not generate a corresponding displacement of the pipe, requires the pipe to be pulled off and the assembly procedure to be repeated. Furthermore, prior art joints are not reliable and resistant in terms of sealing and mechanical locking thereof over the pipe.

The invention has the object of providing a joint of the type as described hereinbefore which can obviate the drawbacks of prior art joints without requiring a complex and costly construction.

The invention fulfils the above objects by providing a joint as described hereinbefore and as

defined in the preamble of claim 1 and wherein the nut has internal threads extending along the conical section of the nut, wherefore clamping or final locking of the pipe on the union can occur in either one of two different modes .

A first mode in which the nut is moved into a wedging position oh the conical widening portion of the union by the pipe itself by a pulling action in the pull-out direction of the pipe and a second mode in which only the nut is pushed in the pull-out direction of the pipe relative to the pipe itself and the union while being rotated in its tightening direction over the conical widening portion of the union while the pipe is being clamped. Advantageously, the threads of the nut may have either a sawtooth section or other types of section to create friction with the outer surface of the pipe.

The internal threads of the nut extends along a part or the whole of the inner surface of the nut. The nut may have a ring of axial extension tabs on the smaller diameter side facing towards the annular abutment shoulder .

The inner surface of the tabs may be smooth or have ridges arranged in various patterns over such surface. Otherwise, the internal threads of the nut may be arranged to also extend along the inner surface of such tabs to that the tabs also form an extension of the conical threaded surface. The threads of the tabs may have structural characteristics identical to or different from the internal threads of the nut.

The nut extension tabs, by their elasticity and the possible provision of ridges or the like, act as elastic means for preliminary crimping of the pipe end

to move the nut together with the pipe, in the clamping mode with the nut being designed to be moved by partially pulling out the pipe, and further allow the nut to remain in its mounted position on the union of the joint, even when no pipe is present, and regardless of any accidental stresses possibly occurring during transport, storage ^* and assembly of the joint.

Also, the elasticity of the tabs allows easy removal of the nut from the union and the gaps between the tabs give evidence of the abutment of the pipe against the radial, particularly annular stop shoulder. tn accordance with a further feature, the outer surface of the nut skirt may be smooth or provided with a ring of axial ribs acting both as gripper means and as nut stiffening or reinforcement means against widening stresses, with the pipe being locked on the union .

This particular form of nut may be provided in combination with a conical widening portion of the union, which may have either a smooth or a stepped configuration or be equipped with a series of disorderly arranged sector-shaped projections and/or annular projections in the form of annular teeth, which are placed in different axial positions of the overall axial extension of the conical widening section . A continuous helical projection may be provided, extending along the conical widening section of the union, from the smaller-diameter end of the conical widening portion to the maximum diameter end. According to yet another feature, said maximum diameter end of the conical widening section of the pipe union may have a lead-in extension formed on a conical surface which tapers in a direction opposite to

that of the conical widening portion, i.e. toward the end of the union designed to be fitted into the pipe.

In this case, the ridge or projection or helical tooth may also extend along said conical lead-in projection.

By this arrangement, the union may be more easily inserted in the ^" pipe, e.g. by rotating it in the tightening direction of the helical tooth or the like , wherefore the union is fitted into the pipe while being guided by said helical tooth and with a lower effort.

The operation of the joint and the assembly thereof over the pipe follow two steps .

In the first assembly step, the pipe is fitted onto the union by being slipped onto the conical section and possibly onto the ridges, crimping edges or crimping rings, if any, i.e. a succession of cylindrical or conical surfaces having increasing diameters and different from each other, which form progressively widening annular step-like portions forming such conical widening section . During insertion of the pipe, the nut, which is mounted on the body, automatically reaches a retracted position behind the union end with the conical widening section . Particularly, the nut is moved back to abutment against the annular shoulder that acts as a limit stop for the union in the pipe, and is also known as retaining ring. Thanks to the provision of the elastic tabs, the pipe is forced into the gap between the union, namely the cylindrical section of the union, and the nut until it contacts the radial stop shoulder. The gaps between the extension tabs of the nut give evidence of the proper abutment position reached by the pipe against the radial shoulder .

The annular stop shoulder may be also omitted in the union: in this case, the length of the pipe section to be fitted onto the union will be selected by the user. Thanks to the particular construction of the nut of the invention, the second step in which the pipe is finally clamped or locked on the union may be carried out in either one of two different modes .

In the first mode, the pipe is pulled in its pull- out direction. During this step, due to the grip effect of the nut threads on the pipe and to the interference created between the pipe and the elastic tabs , the nut becomes integral with the pipe and moves therealong in the pull-out direction. During the pull-out displacement, the tapered threads of the nut and the conical wall of the union clamp the pipe therebetween, the effectiveness of the clamping action being directly proportional to the pull-out force. Particularly, an axial force in the pipe pull-out direction causes the teeth to bend the nut extension tabs , which act as a clamp and allow the teeth to further penetrate the thickness of the pipe wall. The bending tabs effectively add resistance against pull-out of the nut from the pipe and/or of the pipe from the joint. In the second mode, the nut is manually pushed in the pipe pull-out direction relative to the pipe and to the union, i.e. the nut is pushed opposite to the annular shoulder, while being rotated in the helix, i.e. thread tightening direction. The conical walls of the union and the tapered threads of the nut ensure clamping of the pipe, thanks to the above technical effects .

It shall be noted that, thanks to the present invention, two assembly options are provided. The provision of the tapered threads extending all along the inner surface of the nut and possibly over the tabs allows the nut to be "tightened" on the pipe that is fitted on the union. This cannot be achieved by similar prior art products , and is remarkably useful in those applications in which it is not desirable to touch the pipe once it has been laid. For instance, during the system checking step, after installation, the nut can be "tightened" on the pipe without touching or displacing at all the pipe. This advantage is not provided by prior art joints . Once the joint has been mounted on the pipe, any displacement of the nut, caused by shocks or stresses that do not generate a corresponding displacement of the pipe, requires the nut to be repositioned and clamped again on the pipe and any shock that causes the tube to be displaced from its correct position requires the pipe assembly procedure to be repeated.

The presence of the tabs on the nut as a component that assists pipe connection through the action of the helical teeth is also a novel feature . Due to the pulling load in the pipe pull-out direction, the tabs bend and crimp the pipe, thereby exerting an additional clamping effect with respect to prior art joints.

Thanks to the invention, the joint is more flexible during the assembly step and more reliable in terms of pull-out strength of the connection. The invention also relates to further improvements, which form the subject of the dependent claims .

The features of the invention and the advantages deriving therefrom will appear more clearly from the following description of a non-limiting embodiment which is illustrated in the accompanying drawings , in which :

Figures Ia to Id are several different views of a joint of the present invention for connecting two lengths of pipe, which comprises two opposite pipe unions, coassially joined in an intermediate area at the annular abutment shoulder that acts as a limit stop for the pipe on the corresponding unit.

Figures 2a to 2d are several different views of the pipe locking nut cooperating with a pipe union for locking a pipe end thereon . Figure 3 is a sectional view as taken along a central plane parallel to the axis of the union of an enlarged detail of the pipe union .

Figure 4 is the same view as Figure 3 showing the nut fitted over the cylindrical section of the pipe fitting, with the pipe being omitted.

Figure 5 is the same view as Figure 4 , with the pipe being fitted on the union in the limit stop position, and the nut being still displaced against the annular shoulder that acts as a limit stop for the pipe .

Figure 6 is the same view as Figure 5 , in which the joint has been clamped on the pipe by moving the nut to the pipe locking position against the conical widening portion of the union , i.e. by partly pulling the pipe out of the union, starting from the position of Figure 5.

Figure 7 shows , like Figures 5 and 6 , the alternative mode for clamping the pipe between the nut and the conical widening section of the union .

As shown in the figures, the pipe joint, particularly for PE pipes and for driplines , comprises a tubular pipe union 1 for the end of a pipe 2 to be fitted thereon and a nut 3 which allows the pipe 2 to be locked on the union 1.

In a preferred embodiment, the union 1 has an intermediate cylindrical section 101 which has a conical widening portion 201 at one end designed to be fitted in the pipe 2, and an abutment member 301 at the other end, such as a radial shoulder or the like, which forms a limit stop abutment for a length of pipe 2 on the union 1.

This abutment 301 may be also omitted, in which case the length of the pipe 2 to be fitted on the union 1 may be selected by the user as needed.

As shown in Figures Ia, Ib and Ic, a joint for connecting two lengths of pipe 2 is formed by fixing two unions 1, each with an associated nut 3, in opposite and, as shown in Figure Id, axial positions, to form a single union 1 , which has a conical widening portion 201 at each end, an intermediate cylindrical section 101 and possibly a ring-like shoulder 201 which divides the intermediate section 101 into two portions and forms the limit stop abutment for the two lengths of pipe 2.

Three or more lengths of pipe 2 may be also joined together, by interconnecting multiple T-, Y-, cross- shaped unions 1 or the like, each associated to a nut 3 and, in one embodiment, each with a radial or annular shoulder acting as a limit stop for the pipe.

The conical widening portion 201 of the union 1 may have either a smooth wall or, according to a preferred embodiment, radial projections 501 for crimping the pipe 2 and/or disorderly arranged sector- shaped projections.

Particularly, as shown in Figure 3, for easier clamping of the pipe 2 between the union 1 and the nut

3, the conical widening section 201 of the union 1 has stepped widening portions, consisting of a succession of cylindrical or conical surfaces having increasing and different diameters and forming progressively widening stepped annular areas . These areas are arranged in axially adjacent positions to form one or more rings 501 for crimping the pipe 2 onto the union 1.

The number of crimping rings in the conical widening section 201 may change according to the diameter of the joints.

There may be further provided that at least one of said rings or annular projections in the conical widening section 201 is not continuous so that a ring of projections arranged at intervals along the circumference of the union 1.

Otherwise, a series of annular projections, in the form of annular teeth, may be provided in different axial positions of the overall axial extension of the conical widening section 201.

In a further embodiment, at least one continuous helical projection or external threads extend along the conical widening section 201 of the union 1, from the smaller-diameter end of the conical widening portion

201 to the maximum diameter end.

Particularly, the above embodiment facilitates rotation of the nut 3 at the widening area 201 so that the walls of the union 1 and the threads on the inner surface of the nut 3 can clamp the pipe 2 when it is fitted on the union 1.

For easier fitting of the length of pipe 2 over the union 1 up to the shoulder 301, the maximum diameter end of the conical widening section 201 of the pipe union 1 is designed to have a lead-in extension 401. Such lead-in extension 401 has a conical surface which tapers in a direction opposite to that of the conical widening portion 201, i.e. toward the end of the union 1 that is designed to be fitted into the pipe 2 , for easier slipping of the pipe 2 over the crimping rings in the widening area 201 and easier insertion of said pipe in the gap between the body of the union 1 and the nut 2 along the cylindrical section 101 up to the retaining ring 301 or, when such ring is omitted, to a user-selected point. In the embodiments with a conical widening section 201 having radial projections for crimping the pipe 2, the ridge, projection, helical tooth or threads on the conical widening section 201 of the union 1 may be arranged to also extend over said conical lead-in extension 401 to generate a lead-in surface and lead-in threads for easier mounting of the pipe 2 on the joint.

The pipe 2 is locked on the union 1 by providing a nut 3 mounted on the body of the union 1.

As shown in Figure 4, when the joint is open, i.e. available for connection of one end of a pipe 2 , the nut 3 is mounted on the cylindrical section 101 of the union 1 and/or in a retracted position abutting against the radial shoulder that acts as a limit stop 301 for

the pipe 2, when such a shoulder 301 is provided. Conversely, as shown in Figures 6 and 7, when the joint is closed, i.e. when the pipe 2 is clamped between the inner conical surface of the nut 3 and the outer conical surface of the end of the union 1 , the nut 3 is moved, by axial displacement towards the conical widening portion 2 ^* 01 at the end of the union 1 , towards the end of the union 1 opposite to the radial shoulder or the retaining ring 301. As shown in Figure 2c, the nut 3 has an inner conical surface, which conical surface widens towards the fitting end of the union 1 , i.e. the conical end of the union 1. The area with the smaller internal diameter may have such a diameter as to prevent any accidental release of the nut 3 from the union 1.

As shown in Figure 5, in the first step of fitting the pipe 2 onto the joint, the nut 3 mounted on the union 1 is displaced backwards to abutment against the retaining ring 301 as the pipe 2 is fitted onto the cylindrical body 101 of the union 1, which pipe is slipped from the lead-in surface 401 over the crimping rings 501 of the widening section 201, by forcing it into the gap between the outer conical surface 201 and the cylindrical section 101 of the union 1 and the inner conical surface of the nut 3 , until it contacts with the retaining ring 301 or, when said ring 301 is omitted, to a user-selected position. The conical surface of the nut 3 and the elastic tabs 203 allow preliminary elastic engagement between the pipe 2 and the nut 3 when the latter is in the joint opening position.

As shown in Figure 2c, the nut 3 has internal threads 103 which extend along the conical section of the nut 3 thereby forming helical teeth.

In a preferred embodiment, the threads 103 of the nut 3 may have a sawtooth section and said inner threads 103 of the nut 3 extend all over the inner conical surface of ^* the nut 3.

In a preferred embodiment, the nut 3 has a ring of axial extension tabs 203 on the smaller diameter side facing towards the annular abutment shoulder 301.

As shown in Figure 2c and in Figures 5 to 7 , the smaller diameter of the nut 3 at the tabs 203 and the elasticity of such tabs 203 allows the pipe 2 to be fitted in the gap between the joint 3 and the union 1, while generating friction or interference between said pipe 2 and the nut 3.

The inner surface of the tabs 203 may either be smooth or have projections arranged over one or more circumferences or at different points of said surface to increase the crimping action exerted by the inner surface of the nut 3 on the outer surface of the pipe 2.

In a preferred embodiment, the extension tabs 203 also form an extension of the threaded conical surface ^ on the inner side of the nut 3 , the internal threads

403 being also provided along the inner surface of such tabs 203.

The internal threads 403 of the tabs 203 may have the same structural characteristics as the internal threads 103 of the nut 3. As an alternative, the threads 403 on the inner surface of the tabs 203 may be formed with different construction characteristics from the threads 103 on the inner surface of the nut 3. For

instance, said threads 401 may have a different inclination, or different thicknesses and heights from the threads 103 of the nut.

The provision of the tapered threads 103 and 403, e.g. having a sawtooth section, extending over at least a part of the inner surface of the nut 3 , particularly on the body of the nut 3 and possibly on the tabs 203 allows the nut 3 to be tightened onto the union 1 , particularly over the conical widening section 201. The step of tightening the screw nut 3 onto the union 1 during the joint closing step cannot be successfully carried out in prior art joints and is useful in applications requiring the pipe not to be touched once it has been laid. Particularly during system check, after installation, or during recovery of joints whose nut is displaced from its correct closed position due to shocks or stresses, the internal threads 403 and 103, both on the body of the nut 3 and, in one embodiment, on the tabs 203, allow the nut 3 to be tightened onto the pipe 2 and the union 1 without touching or displacing at all the pipe.

While Figure 3a shows three tabs 203 the number of tabs 203 can change according to the diameters of the unions 1. In the joint opening condition, i.e. when the pipe

2 is not fitted on the union 1 and the nut 3 is mounted on the cylindrical section 101, the diameter of the nut

3 at the tabs 203 and the elasticity of said tabs 203 are such as to prevent the nut 3 from being accidentally pulled out of the union 1. Therefore, the nut may be only slipped out of the union by applying enough force to open the elastic tabs 103 apart and

only allow its passage beyond the conical widening section 201.

Therefore, the tabs 203 may act as spread-apart means for disengagement of the nut 3 from the union 1. As shown in Figures 2a, 2b, 2c, the extension tabs 203 of the nut 3 are separated from each other by inspection gaps , which are used to check abutment of the pipe 2 against the radial , particularly annular abutment shoulder 301. These gaps allow to check that the position of the pipe 2 during the first step of fitting the pipe 2 onto the joint is correct, i.e. that the pipe is in contact with the retaining ring 301.

Once the pipe 2 is placed between the union 1 and the nut 3 , final clamping or locking of the pipe 2 on the union 1 is obtained in either one of two different modes .

As shown in Figure 6, in a first clamping mode the nut 3 is moved by partially pulling out the pipe 2 , i.e. the nut is moved to a wedging position on the conical widening portion 201 of the union 1 by the pipe itself, by a pulling force in the pull-out direction of the pipe 2. Particularly, by pulling the pipe 2 in the pull-out direction, the gap between the inner surface of the nut and the inner surface of the union 1 progressively decreases from the cylindrical section 101 toward the widening area 201 until the pipe 2 is clamped.

During this step, due to the grip effect of the threads 103 of the nut 3 on the pipe 2 , the nut 3 becomes integral with the pipe 2 and moves therealong in the pull-out direction. As the pipe 2 and the nut 3 are slipped over the union 1 from the retaining ring 301 towards the widening area 201, the tapered threads

103 of the nut 3 and the conical widening area 201 of the union 1, particularly the crimping rings 501, clamp the pipe onto the joint, the effectiveness of the clamping action being directly proportional to the force in the pull-out direction of the pipe 2.

As the pipe 2 is pulled out, the extension tabs 203 of the nut 3 act as elastic means for preliminary crimping of the end of the pipe 2 and moving the nut 3 together with the pipe 2 , their internal diameter allowing the pipe 2 to be clamped between them and the cylindrical section 101 of the union 1 with such a force as to ensure preliminary engagement of the pipe 2 within the nut 3.

Furthermore, the tabs 203 effectively increase the pull-out resistance of the joint. Particularly, thanks to the friction between the projections on the inner surface of the tabs and the outer surface of the pipe , the axial force in the pull-out direction of the pipe 2 causes the tabs 203 to bend and act as a clamp, thereby allowing the teeth and/or the projections to further penetrate the pipe 2. Therefore, the tabs 203 have an additional clamping effect as compared with similar joints, thanks to the action of the helical teeth and/or projections, and prove to be an important component for connection of the pipe 2 on the joint.

As shown in Figure 7 , in a second mode for clamping the pipe 2 onto the joint, only the nut 3 is pushed in the pull-out direction of the pipe 2 relative to the pipe 2 itself and the union 1 while being rotated in its tightening direction over the conical widening portion 201 of the union 1 while the pipe 2 is being clamped.

Like in the previous mode, the progressively widening annular stepped areas or the crimping rings 501 in the conical widening area 201 and the internal threads 103 of the nut 3 allow the pipe 2 to be clamped between the union 1 and the nut 3 while preventing the pipe from being moved in the pull-out direction , i.e. while leaving the end of said pipe 2 in contact with the retaining ring 301.

As shown in Figures 2a and 2b, for an easier grip and rotation of the nut 3, said nut 3 may have a ring of axial ribs 303 on the outer surface of its skirt, which act both as gripper means and as means for stiffening or reinforcing the nut 3 against widening stresses, with the pipe 2 being locked on the union 1. Thus, the above features provide increased flexibility of the joint during assembly, allowing for different clamping modes , as well as improved reliability in terms of pull-out resistance of the connection . Obviously, the invention is not limited to the embodiments described and illustrated herein, but may be greatly varied, without departure from the guiding principle disclosed above and claimed below.