AU2008220767B2 - Joint for connecting pipes - Google Patents

Description

WO 2008/104562 PCT/EP2008/052367 GEORG FISCHER TPA SRL. Joint for connecting pipes. The present invention relates to a joint for 5 connecting pipes composed of a body provided at least at an end with an outer thread; a cylindrical seat for inserting the pipe inside said body; a ring nut intended to be screwed at the end of said body on the thread, said ring nut being provided with an inner 10 conical surface; at least a clamping ring with an outer shell surface that is at least partially conical and intended to cooperate with the inner conical surface of said ring nut and which ring internally has teeth intended to grip the end of the pipe inserted in the 15 joint and said ring having the possibility of being tightened by means of a radial restriction caused by the ring nut being screwed on the body, at least a seal between the cylindrical seat of the joint and the outer wall of the pipe. 20 Joints of this type are known and widely used. The joint is assembled and then tightened on the pipe generally according to the following sequence of steps: According to a first step, the pipe is introduced 25 into the joint which is in its pre-assembled condition and with the tightening ring nut already screwed on the thread. The tightening ring nut is in an initial screwing condition wherein the clamping ring is not compressed against the pipe for clamping it into the 30 joint yet, while the seal has such a diameter to allow WO 2008/104562 PCT/EP2008/052367 the pipe to slide inside it generating a frictional resistance that can be easily overcome by a manually applied force. Therefore the pipe can slide inside the clamping ring and the seal being brought in the proper 5 coupling position into the joint body. Once the pipe has reached the complete coupling position, it is mechanically clamped by screwing the tightening ring nut acting on the clamping ring by means of respective conical surfaces. In some 10 cases, it can be also provided for the tightening ring nut to exert an axial compression on the seal by means of the axial movement along the joint body that is transmitted to the clamping ring and in this case it acts also as seal pushing means. 15 In all above mentioned variants, the inner conical surface of the ring nut is pushed to contact the conical surface of the end of the clamping ring so when the ring nut is screwed the axial advance of the ring nut causes a radial constriction of the clamping 20 ring gripping the pipe wall by a series of conical inner teeth due to the relative sliding motion of two conical surfaces of the above mentioned two parts. Although these joints serve their function in a satisfactory way, they have some drawbacks, 25 particularly when the joint is inserted and clamped on the pipe. Joints for pipes commercially available, have a type of clamping ring, whose inner diameter is slightly smaller than the outer diameter of the pipe therefore 30 said ring is elastically deformed, i.e. it is slightly 2 WO 2008/104562 PCT/EP2008/052367 widened, when the pipe is inserted in the joint and such deformation causes an intrinsic force for the elastic returning action in the original/not stressed position to be generated by means of which, inner teeth 5 of the ring, by gripping the outer surface of the pipe allow the ring to be firmly tightened thereon. The above clamping ring carries out its function by its physical structure/shape, being composed of a ring, usually a plastic one, having an axial open slot 10 at both head sides. Therefore the clamping ring is inserted by forcing it on the pipe and this leading to: both a certain difficulty for inserting the pipe in the joint, and the fact that, when the pipe is taken out from the joint, 15 such ring remains clamped on the pipe, since the gripping action of teeth thereof does not allow the ring to slide on the outer surface of the pipe, towards the end thereof housed in the joint. Therefore for removing the clamping ring from the 20 pipe, it is necessary not only to unscrew the ring nut from the body and to take off the pipe with the ring still gripped thereon, but it requires an external operation by the user, i.e. the application of a certain force, particularly intended for widening the 25 ring. Said force has to be applied between the two ends of the ring generated by the axial slot in order to oppose and overcome the elastic return force that, on the basis also of the size of the pipe and consequently of the thickness of the clamping ring, can be difficult 30 to be opposed by the user. In addition to this there is 3 WO 2008/104562 PCT/EP2008/052367 also the fact that even only the simple gripping action for applying a sufficient force is difficult, the axial slot being somewhat narrow, and it is often necessary the help of some tools for levering the two ends of 5 said slot. A further drawback of joints actually on the market, is the fact that the clamping action by the ring on the pipe cannot be easily reproduced. This drawback, is caused by two facts: the first one is that 10 the ring is clamped on the pipe by two forces: an intrinsic elastic return force, previously described, that can clamp the ring on the pipe in a wrong position, and a tightening force by the radial restriction deriving from the tightening/pressing 15 action determined by screwing the ring nut on the body. The second fact is that due to the coupling action the clamping ring/ring nut that is generally made with a conicity of about 8-10 degrees causes also a very high screwing length on the body. That causes also high 20 positioning allowances between the ring nut, the clamping ring, the pipe and the body with a low repetitiveness of the same relative position of said parts in the optimal condition tightening and clamping the pipe. Therefore it is not possible to provide 25 effective references for the right positioning for screwing the ring nut on the body and the pipe can take various positions for the axial insertion in the body in various possible clamping conditions, pipes being also variable in their outer diameter even if within 30 specific tolerances regarding both size and 4 WO 2008/104562 PCT/EP2008/052367 ovalization. By screwing the ring nut on the body the conical inner surface of said ring nut interacts with the conical outer shell surface of the clamping ring, and 5 such interaction causes the ring to be tightened, consequently leading to a more firm clamping action of the ring on the joint. However the above tightening action, deriving from the ring nut being screwed, as it is easy to understand, depends on how much such ring 10 nut is screwed on the body, and consequently, it is a force that depends directly on the sensitiveness of the person using the joint, which is a characteristic fully subjective as it can be obviously understand. The angle of inclination of conical walls with 15 respect to the central axis of the cone defined by said conical walls defines the travel of the ring nut necessary to tighten the pipe in its clamped condition. An acute angle, so wherein the conicity is relatively small, i.e. conical surfaces are slightly inclined with 20 respect to the central axis of the cone defined by said conical walls results in a relatively low torque for screwing the ring nut, but the travel necessary for obtaining a sufficient tightening action is relatively long so the ring nut has to be turned a lot of time 25 when screwing it. The increase in the conicity and so in the inclination of conical walls with reference to above mentioned definitions of said inclination results in a shorter tightening travel, but a greater tightening 30 torque is necessary. 5 Therefore the choice of the inclination is generally a compromise in comparison with joint functionalities. On one hand the fact of having the highest tightening and so clamping effect of the pipe into the joint is 5 desired, but without the need of a too high effort being possible to exert it even only manually for a large range of pipe diameters, and i.e. without using tools. Concerning the conical shape, for such reasons as mentioned above the clamping action of the ring on the 10 pipe cannot be perfectly reproduced thus leading to the fact that often the joint does not work in its optimal conditions. Any discussion of documents, acts, materials, devices, articles or the like which has been included in 15 the present specification is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this 20 application. Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, 25 but not the exclusion of any other element, integer or step, or group of elements, integers or steps. According to the present invention, there is provided a joint for connecting pipes composed of a body provided at least at an end with an outer thread; a cylindrical 30 seat for inserting the pipe inside said body; a ring nut intended to be screwed at the end of said body on the thread, said ring nut being provided with an inner conical surface; at least a clamping ring with an outer shell surface that is at least partially conical and intended to 35 cooperate with the inner conical surface of said ring nut and which ring internally has teeth intended to grip the 6 end of the pipe inserted in the joint and said ring having the possibility of being tightened by means of a radial restriction caused by the ring nut being screwed on the body, 5 wherein said clamping ring has an intrinsic elastic force for firmly maintaining a condition wherein its inner diameter is slightly greater than the outer diameter of the pipe so that the latter can be inserted by an axial sliding action without any impediments in the clamping ring, and 10 said clamping ring can be elastically deformed narrowing the inner port delimited by the ring, against the action of said elastic force in a condition with the diameter reduced with respect to the diameter in its resting condition, at such an extent that teeth of the ring grip the outer wall 15 of the pipe by firmly clamping it inside the joint, said reduction being generated by the action of the conical surface of the ring nut on the conical surface of the clamping ring during the screwing action, wherein the clamping ring has a projecting annular 20 tooth intended to elastically interact with the annular fitting groove obtained in the cylindrical wall of the seat. According to a characteristic of the present joint, the clamping ring has two crowns of opposite axial 25 slots and they are open alternatively on one of the two opposite head sides so to give the plane development of the shell surface of the clamping ring a shape that can substantially resemble a linked series of letters S. A first crown of separating axial slots, is composed 30 of slots such to form a crown of axial tongues retained on a material continuous annular support and such tongues can be circumferentially compressed against the outer surface 7 of the pipe, said slots being open only at one of the head sides of the ring. A second crown of axial slots comprises at least one or more intermediate axial slots provided at a median position of each axial tongue formed 5 by the above first crown of slots. Intermediate slots of said second crown of slots are open at the side opposite to the preceding ones and have such a depth in the body of the axial tongues that is enough to guarantee a certain circumferential elasticity. This allows the crown of 10 tongues to make elastic radial changes even if it can be preferably made of a relatively rigid plastic material These radial changes obviously occur together with restrictions or extensions i.e. 7A WO 2008/104562 PCT/EP2008/052367 shortenings and/or elongations of the circumference of the clamping ring due to the presence of axial slots and particularly of the two axially opposed crowns. Slots have such an axial length that they end beyond a 5 circumference provided in an intermediate position and particularly in the median position of the axial length of the clamping ring. This arrangement advantageously allows to have different changes of the radius of the two axial ends of the clamping ring so that it may take 10 a condition wherein the shell wall conically becomes widener from one end to the other head end or vice versa it becomes conically narrower from said one to said other end. According to a further characteristic of the 15 present joint it has an initial entrance region having a diameter greater than the outer diameter of the clamping ring and an annular groove for fitting an annular tooth retaining the clamping ring which tooth engages by snapping in the groove by retaining the 20 clamping ring in a condition engaged in the body, with a predetermined retaining force and such that the ring can be disengaged from the body by a manual action. Advantageously with the clamping ring engaged in the body, said ring, by means of the presence of the 25 second crown of axial slots and by means of the behaviour of the clamping ring under the elastic compression or extension stress, said clamping ring, is slightly elastically circumferentially deformed that is its inner port is slightly narrowed, still however 30 guaranteeing an inner diameter of said port greater 8 WO 2008/104562 PCT/EP2008/052367 than the outer diameter of the pipe. Said slight circumferential deformation of the side of the ring intended to be inserted in the body of the joint, i.e. the side of the ring having on its outer shell surface 5 the annular retaining tooth, causes the tongues of the clamping ring projecting towards the entrance side of the body to slightly outwardly open wide with respect to the central axis of the joint obtaining a flower like opening whose petals are composed of tongues of 10 the clamping ring. Such configuration gives the pipe a port, when it is inserted, having a greater diameter with respect to the inner diameter of the clamping ring in the resting condition with the ring inserted in the body. 15 Advantageously the force coupling the ring in the body is such that it is greater than the force generated by possible slipping effects of the pipe when it slides. According to a further characteristic of the 20 present joint the clamping ring, on its outer surface, particularly at the end of the ring intended to elastically interact with the annular fitting groove in the inner wall of the seat for the insertion of the pipe, has a projecting annular tooth. 25 It is possible that similalry to the state of the art, the opposite end of the outer surface of the ring, i.e. the end intended to elastically interact with the ring nut, has a wedge-like or conical inclined surface, which wedge-like or conical surface has the same 30 inclination or an inclination consistent with the inner 9 WO 2008/104562 PCT/EP2008/052367 conical surface of the ring nut that interacts when it is screwed on the body. According to a further characteristic of the present joint the clamping ring on its inner surface, 5 at the end intended to clamp the pipe in the joint, has one or more teeth that make one or more series of crowns of teeth. According to a variant embodiment of the present joint, said peaks of teeth making the one or more 10 series of crowns of teeth of the clamping ring, preferably lie on two or more axially adjacent circumferences and said circumferences are concentric having such diameters that progressively reduce their own value from the outermost crown of teeth, i.e. the 15 one at the end of the clamping ring, to the innermost one. By means of the above flower-like configuration of the tongues of the clamping ring, generated by inserting it in the body of the joint, when said ring 20 is tightened against the outer surface of the pipe, a progressive clamping of the axial crowns of teeth is achieved. In other words, teeth of the axial crowns do not contemporaneously grip the outer surface of the pipe but such interaction occurs progressively from the 25 innermost crown of teeth, to the outermost one. Thus a greater penetration of the first series of teeth of the crown is obtained by considerably reducing the initial effort screwing the ring nut for clamping the pipe that in many cases is also a manual effort and i.e. without 30 using tools. 10 WO 2008/104562 PCT/EP2008/052367 A first embodiment of the present invention, provides mutual abutting conical surfaces and that is the inner one of the ring nut and the outer one of the clamping ring provided at the end thereof outside the 5 seat of the pipe in the body of the joint, to have a relatively abrupt inclination and comprised between 25 and 40* preferably about 30*. By this relatively abrupt inclination of the conical surface, (corresponding to an opening angle of the cone of 60*) it is possible to 10 obtain a sealing tightening of the joint on the pipe by a screwing rotation of the ring nut of about half a turn. This is particularly advantageous as regards the speed of intervention especially under uncomfortable working conditions. Obviously the short rotation of 15 half a turn is also for loosening the joint from the tightened condition of the pipe to freely take out the pipe from the joint. The lower radial compression force exerted by the ring nut on the tongues of the clamping ring, with 20 respect to a lower inclination of the cooperating conical surfaces of the clamping ring and of the ring nut, is compensated for the fact that by means of the particular flower-like configuration of the clamping ring, in the not tightened condition of the joint but 25 in its mounted condition, the tongues are arranged as to be open wide and the radial compression action exerted thereon by the ring nut resembles to an oscillation of said tongues, so that when on the tongues two or more crowns of inner radial teeth are 30 provided which are arranged along one of two or more 11 WO 2008/104562 PCT/EP2008/052367 circumferences respectively having a different axial position with respect to the extension of said tongues, the compression exerted by the ring nut on the tongues causes one of the two or more crowns of teeth to grip 5 the pipe at a time and in a progressive way with reference to the axial direction towards the end of the clamping ring cooperating with the ring nut. Substantially as the tightening action occurs and so the tongues are axially compressed they change their 10 position from an outwardly inclined position with respect to the pipe to a position parallel or slightly inclined towards it, so teeth of each crown that is nearest the conical end of the clamping ring grip the pipe after the ones of the crown that is immediately 15 adjacent and more far away from the conical end of the clamping ring. Therefore the initial compression force is substantially distributed always only on one of the two or more crowns of teeth. A second embodiment of the present invention, 20 provides a joint of the type described hereinbefore wherein the conical surface at the head end of the clamping ring faced towards the tightening ring nut and the inner conical surface at the end of the tightening ring nut opposite to the threaded portion of the joint 25 body have two adjacent portions having a different inclination with reference to the central axis of the pipe and/or tightening ring nut and/or clamping ring, a first portion of said conical surface, at the end of the clamping ring and at the corresponding end of the 30 tightening ring nut, having an inclination (with 12 WO 2008/104562 PCT/EP2008/052367 respect to said central axis of the pipe and/or ring nut and/or clamping ring) that is greater than the inclination of a second portion of the conical surface to which said first conical surface portion is 5 connected in the direction of the threaded portion of the joint body, i.e. in the direction for introducing the pipe into the joint. Advantageously the inclination of the second conical surface portion is substantially the same both 10 as regards the conical surface of the tightening ring nut and as regards the conical surface of the clamping ring. The inclination of the first conical surface portion of the tightening ring nut on the contrary is 15 different from and slightly lower than the inclination of the first conical surface portion of the clamping ring. Advantageously on the clamping ring, the first conical surface portion is connected to the second 20 conical surface portion by a rounded or beveled arcuate portion, while as regards the tightening ring nut the two first and second conical surface portions are connected by an angle. By means of this, during the relative sliding of 25 conical surfaces of the ring nut against conical surfaces of the clamping ring, upon the passage from the condition wherein the two second conical surface portions of the tightening ring nut and of the clamping ring having a lower inclination interact one with the 30 other, i.e. when they contact each other, to the 13 WO 2008/104562 PCT/EP2008/052367 condition wherein the two first conical surface portions of the tightening ring nut and of the clamping ring interact one with the other, i.e. when they abut and slide one on the other, there are no abutment steps 5 that can cause the clamping ring to slide lesser on conical surfaces of the tightening ring nut, but on the contrary the connecting beveled, rounded area or the like between the two conical surface portions of the clamping ring causes said clamping ring to have only a 10 tangent line against conical surface portions of the tightening ring nut in the angled area connecting said portions. According to a preferred embodiment, the first conical surface portion has an inclination with respect 15 to the central axis of the pipe and/or tightening ring nut and/or clamping ring greater than 30 and lower than 80*, and preferably it is from 40* to 600, particularly from 450 to 50*. As regards the second conical surface portion, it 20 has an inclination lower than 40*, preferably lower than 30* and particularly from 100 to 30*. Due to characteristics of the present invention, in the same type of joint advantages deriving from different inclinations of conical surface for the 25 contact between clamping ring and tightening ring nut are obtained. Second conical surface portions having the lower inclination or conicity allow teeth of the clamping ring to be pushed into the pipe wall by a relatively poor effort, resulting in a first effective 30 gripping of the ring on the pipe, and in addition it 14 WO 2008/104562 PCT/EP2008/052367 results in an axial travel for compressing the annular seal, while once such condition is obtained, the additional compression of teeth of the clamping ring into the pipe wall is achieved firstly by means of 5 hydraulic pressure of the fluid when exceeding a certain pressure completing the gripping action caused by the first cone and then by a short tightening travel since such effect is obtained when the tightening ring nut and the clamping ring cooperate one with the other 10 with corresponding first greatest conical surface portions, even when the movement tightening the ring nut is completed. The fact that said first conical surface portions have a greater conicity leads to a greater retaining action of the pipe in the direction 15 withdrawing it when the inner pressure reaches very high values or under strong mechanical pulling conditions of the pipe applied to the joint. Moreover due to the abruptness of said conical surfaces of said two first portions a possible movement of the pipe with 20 respect to the joint due to the inner pressure or to the pipes being pulled from the joint automatically causes teeth of the clamping ring to highly increase their compression in the pipe wall and so to increase the force or resitence clamping the pipe. 25 According to a further characteristic of the present joint there is provided a seal of the pipe inside the joint, which seal is housed in a suitable seat obtained inside the body, and in the resting condition, i.e. with the joint not tightened on the 30 pipe, it has an inner diameter greater than the outer 15 WO 2008/104562 PCT/EP2008/052367 diameter of the pipe or substantially equal to the outer one of the pipe said inner diameter of the seal being such that it allows the pipe to be freely slidably inserted in the joint without any impediments, 5 while with the joint tightened on the pipe, caused by the ring nut screwed on the body, said seal is elastically deformed such that its inner diameter is smaller than the outer diameter of the pipe so that in said deformed conditions it tightly adheres against the 10 outer surface of the pipe, guaranteeing the desired hydraulic sealing effect, while when the joint is released from the pipe, said seal has such an intrinsic elasticity that it elastically recovers its original resting shape either spontaneously or at least 15 partially by means of the drawing action of the pipe when it is taken out from the joint and under said condition it allows the pipe to slide in the direction taking it out from the joint without it interfering with said seal to deform it. 20 The annular seal for example is of the O-ring type or the like. Said annular seal is housed in an enlargement of the seat for the insertion of the pipe with a slightly conical shell wall. An embodiment of the invention provides the seat 25 of said annular seal of the O-ring type or the like to be composed of a radial enlargement of the seat of the pipe in the body of the joint which enlargement has a slightly conical shell surface which conical shell surface ends by an annular shoulder at the end opposite 30 to the one for inserting the pipe. The smallest 16 WO 2008/104562 PCT/EP2008/052367 diameter of said conical narrowing or reduction is however greater than the outer diameter of the pipe and the conical shell surface has an axial length that is slightly greater than the diameter of the cross section 5 of the O-ring annular seal. With the joint in its not tightened conditions, the annular seal is housed in the slightly conical portion having the greatest diameter. When the joint is tightened on the pipe by screwing the tightenend ring nut, axial pushing means provided in 10 the joint act on the seal, are automatically driven by the tightening movement of the ring nut and they push the seal against the annular shoulder at the end having the smallest diameter of the conical shell surface of the seat of the seal, while diametric size of said 15 conical shell, of the pipe and of the seal are such that with under the not tightened condition the pipe can freely axially slide in the seal and with the joint in its tightened condition the seal is tightly forces in the narrowing portion between the pipe and the wall 20 of said narrowing and it is elastically circumferentially deformed so that its inner diameter is smaller than the outer diameter of the pipe. When the joint is released from the pipe, the seal of the O-ring type or the like can elastically return 25 in its initial position i.e. in the conical narrowing portion having the greatest diameter and such elastic return occurs either spontaneously, or at least partially by means of the drawing action of the pipe when it is taken out from the joint. When the pipe is 30 taken out from the joint a friction between the annular 17 WO 2008/104562 PCT/EP2008/052367 seal and the pipe and the annular seal and the opposite conical shell surface of the seat of the seal is originated. As previously described, the configuration of said seat of the annular seal of the O-ring type 5 being slightly conical and having a length close to the diameter of the longitudinal section of the annular seal, when the pipe is taken out from the joint, said seal recovers its initial position i.e. near the region of the conical shell surface characterized by the 10 greatest diameter, thus allowing the pipe to be freely taken out from the joint. In conventional joints, on the contrary there is provided a seat of the annular seal having a cylindrical shell surface and/or an axial extension of said shell surface that is really greater 15 than the diameter of the cross section of the annular seal of the O-ring type. Therefore due to such configuration, when the pipe is taken out from the joint, the seal remains embedded against the annular shoulder and/or it is subjected to a kind of unnatural 20 twisting due to the friction with the outer surface of the pipe and the wall of seat of the seal. Due to above effects, in known joints it is necessary to position again the annular seal in order to give it its original shape if the pipe is desired to be again inserted in 25 its seat of the joint after it has been previously taken out, since the deformed seal or embedded in the seat has an inner diameter smaller than the one of the pipe and so it cannot be inserted. By means of the above configuration of the present joint on the 30 contrary such repositioning of the seal is not 18 WO 2008/104562 PCT/EP2008/052367 necessary since as previously mentioned the annular seal recovers its initial position without any external operations, thus allowing the free sliding in the direction for re-inserting the pipe in the joint. 5 An alternative variant embodiment of the invention provides the seat of said annular seal of the O-ring type or the like to be composed of an inner annular radial shoulder making an abutment radial surface for the seal. Such radial abutment surface is oriented 10 radially from the axis of the pipe and it is faced towards the tightening ring nut that is it is faced in a direction opposite to the direction introducing the pipe, while the seal is housed in an inner radial groove in the shell wall of a coupling union for the 15 pipe. Such groove is delimited at the side opposite to the annular shoulder, of said coupling union, by a radial narrowing composed of two opposing conical surfaces, the conical narrowing surface faced towards the annular abutment shoulder being a surface for 20 wedging the annular seal when said seal is pushed in the direction withdrawing the pipe. With the pipe not engaged in the seal, the difference between the outer diameter of the pipe and the inner diameter of the seal is from 0,5 mm to 3 mm, 25 particularly from 1 to 2. The radial groove has such a diameter that the seal housed in said groove and in its resting condition has an inner diameter that is slightly shorter than the outer one of the pipe the difference being such that 30 the pipe can be introduced inside the union and through 19 WO 2008/104562 PCT/EP2008/052367 the tight seal without too much resistence. The annular narrowing has a radial projection of 0.1 to 0.5 mm, preferably from 0,2 to 0,4 mm in the direction of the joint or the chord of the O-ring. 5 The shell conical surface has an axial lenght that is slightly greater than the diameter of the cross section of the O-ring annular seal. With the joint not tightened, the annular seal is housed in the portion having the greatest diameter. 10 According to a further embodiment of the present joint the seal of the pipe inside the joint, in its resting condition, i.e. with the joint not tightened on the pipe, has an inner diameter greater than the outer diameter of the pipe or susbstantialy equal to the 15 outer one of the pipe said inner diameter of the seal being such that it allows the pipe to be freely inserted by sliding inside the joint with no obstacles, while, when the joint is clamped on the pipe, by screwing the ring nut around the body, said seal is 20 elastically deformed such that its inner diameter is shorter than the outer diameter of the pipe so under such deformed conditions it tightly adheres to the outer surface of the pipe, thus guaranteeing the desired water-tight effect. 25 When the joint is unclamped from the pipe, on the contrary, said seal can elastically take again its original resting shape either in a spontaneous manner or by means of at least partially the action dragging the pipe when it is withdrawn from the joint and under 30 such condition it allows the pipe to slide being 20 WO 2008/104562 PCT/EP2008/052367 withdrawn from the joint without interacting with said seal thus not deforming it. From the above it is clear that one of the main advantages of the present invention is the joint 5 tightened on the pipe being intended to absorb axial movements due to such high pressures of the fluid and also to use them and said withdrawing movements in order to generate a condition increasing the clamping force and/or the sealing condition. 10 Still another variant embodiment of the joint according to the present invention provides the annular seal to be of the lip type or the like. Said lip seal has a base ring and an extension/lip attached to an end of the inner surface of the base 15 ring. In this case the seat of the annular lip seal is composed of a cylindrical wall and an annular axial abutting shoulder of the base ring. The inner surface of the base ring is cylindrical 20 or if necessary slightly conical for allowing the elasticity to increase and also the elasticity to be adjusted. Said abutting shoulder of the base ring of the lip seal has an abutting surface that is preferably 25 slightly inclined with the inclination having a direction equal to the direction of the conical surface of the ring nut. According to a further characteristic of the present joint the base ring of the lip seal has a cross 30 section that resembles a right-angled trapezium which 21 WO 2008/104562 PCT/EP2008/052367 oblique side has such an inclination to be complementary with the annular abutting shoulder of the seal on the body. Advantageously the inner diameter of the base ring 5 of the lip seal, when it is not stressed, is greater than the outer diameter of the pipe, while the inner port delimited by the lip of said seal, has an inner diameter smaller than the outer diameter of the pipe, but it is such that when the pipe is inserted in the 10 body the lip of the seal cooperates with the outer surface of the pipe but only by means of a slipping action so that the lip, of said lip seal, does not lead to a physical impediment for inserting the pipe in the body of the joint so it is freely inserted in the 15 joint. This is also in the case if the joint is not thightened when the pipe is taken out from the joint. By inserting the pipe in the joint, but with the joint not tightened on the pipe, the radially outer surface of the lip of the lip of the seal, overlaps the 20 radially inner surface of the base ring of said seal, thus forming a kind of circular space with a wedge shaped cross section between said two surfaces; at the same time the radially inner surface of the lip, rests against the outer surface of the pipe without 25 preventing it to be easily taken out from the body, while with the joint tightened on the pipe, there are provided suitable pushing means which axially act on the base ring of the seal by pushing it against the annular abutting shoulder of the body and by 30 circumferentially expanding it, which espansion leads 22 WO 2008/104562 PCT/EP2008/052367 to a pressure on the lip of the seal allowing the inner surface of said lip to adhere by a pressing action against the outer surface of the pipe so to generate the desired hydraulic sealing effect. 5 According to a further characteristic of the present joint, when the joint is tightened on the pipe, the inclination of the surface of the annular abutting shoulder, makes a kind of compression such that, the elastic deformation of the base ring following it leads 10 to a deformation of the inner surface of the base ring of the seal. In the operating condition of the joint, i.e. with the joint in its tightened condition on the pipe and with the fluid passing in the pipe, the circular space 15 having a wedge-shaped section is flooded by the fluid, that, by acting on the inner surface of the lip of the seal, pushes said lip against the outer surface of the pipe, thus coopoerating with the pushing action of the base ring following the elastic deformation thereof 20 made by pushing means, thus increasing the hydraulic sealing effect of the seal. Moreover it results that the intensity of the action of the fluid on the inner surface of the lip, of the lip seal, it substantially directly proportional to 25 the pressure of the fluid inside the pipe therefore an increase of the action of the liquid pressure on the lip can be associated to an increase in the pressure of the fluid in the pipe consequently increasing the hydraulic sealing effect. 30 According to a further characteristic of the 23 WO 2008/104562 PCT/EP2008/052367 present joint when the pipe is released from the joint the lip seal can elastically and spontaneously recover its initial shape under not stressed conditions, thus allowing the pipe to be taken out from the joint 5 without any mechanical and/or excessive friction impediments. According to a further characteristic of the present joint means for pushing the seal, both of the O-ring type or the like or of the lip type, are 10 composed of the combination of the ring nut and the clamping ring which have conical or cylindrical cooperating surfaces that cooperate one with the other when the ring nut is screwed on the body. Once the ring nut has been screwed on the body, 15 the clamping ring is elastically circumferentially tightened against the outer surface of the pipe and at the same time it is axially pushed inside the body. According to a technical solution of the present joint, obviously the material composing the clamping 20 ring has an hardness greater than the one of the material composing the pipe. Such technical solution is absolutely necessary for causing teeth of the axial crowns of the clamping ring to grip the outer surface of the pipe. 25 According to a further characteristic of the present joint the axial movement of the clamping ring inside the body leads the ring to be axially pushed/compressed against the annular seal. Obviously the use of the seal both the O-ring type 30 or the like, and the lip type, as well as of 24 WO 2008/104562 PCT/EP2008/052367 manufacturing arrangements regarding the inner configuration of the body of the joint, particularly as regards the seat of said annular seals, leaves out of consideration the use of the particular type of 5 clamping ring previously described and made according to the present invention. Above described characteristics of the joint regarding the seal can be used by providing also the use of simple clamping rings currently on the market. 10 Such types of seals and parallely inner configurations of the body, particularly as regards the seat of said seals, allow to overcome a series of problems regarding the step inserting and taking out the pipe in/from the joint. By using conventional 15 seals, which have an inner diameter slightly smaller than the outer diameter of the pipe, there is the risk of damaging the seal when the pipe is inserted in the joint, since as it is easy to understand the pipe is inserted by elastically forcing it in the seal housed 20 in its seat. Due to the action inserting the pipe in the joint, the edge of the outer surface of the pipe acts by a cutting action against the inner surface of the seal, since said edge of the pipe, resulting from cutting the pipe, can be particularly sharp or slightly 25 chipped. Moreover still in the step inserting the pipe in the joint, due to the fact that the pipe interacts by a considerably sliding action on the inner surface of the seal by a friction intereference between the two walls, often there is the risk of giving bending or 30 twisting effects to the seal such to damage it for 25 WO 2008/104562 PCT/EP2008/052367 these reasons not guaranteeing a suitable hydraulic effect. The risk of giving to the seal the above unnatural twisting effects is also present when the pipe is taken out from the joint. 5 On the contrary as previously mentioned, said problems do not exist by using seals and inner configurations of the body of the joint according to the present invention. According to a further characteristic of the 10 present joint the body can be provided with limit stops for screwing the ring nut. Such screwing limit stops are composed of one or more surface abutment projections constituting indicators and/or limiting means of the screwing travel 15 of the ring nut on the body, which indicators and/or limiting means allow the user of the joint to tighten the ring nut on the body such to always guarantee the optimal operation of the joint. According to a preferred embodiment of the present 20 joint the body can be provided with means for temporary positioning and retaining the ring nut partially screwed on the joint body and wherein the pipe can be inserted into the joint through the ring nut, the clamping ring and the seal that, under such partial 25 screwing condition, have an inner diameter greater than or substantially equal to the one of the pipe and being such to allow it to pass without an excessive effort, which means retain the ring nut under said partial screwing condition in a temporary way and by force that 30 can be manually overcome. 26 WO 2008/104562 PCT/EP2008/052367 According to a preferred embodiment, said means are composed of at least a radial projection in the trajectory corresponding to the peak of an outer thread of the coupling union for the pipe, which projection 5 can be elasically deformed by a predetermined manual force and which projection cooperates with engaging nothces or grooves provided at the head side of the tightening ring nut faced towards the joint body. Advantgeously, said projection or projections have 10 a protrusion slightly greater than the depth of grooves of the inner thread on the tightening ring nut, therefore the engaging interaction of said projection or projections is in the area of the head side of the tightening ring nut, while once said projections 15 penetrate into the ring nut thread they freely move into grooves of said inner thread being elastically bent and resulting in a slight friction. Again according to a further characteristic of the invention that can be provided as an alternative or in 20 combination with one or more of previous characteristics, the joint of the present invention is provided with anti-rotational means preventing the ring nut from being unscrewed once it reaches the predetermined tightening stop position. 25 In this case said anti-rotational means are composed of one or more radial teeth having the front faces faced towards the ring nut at a radial plane that is slightly upstream than the radial plane where the head side of the tightening ring nut faced towards the 30 joint body falls once the ring nut is in the final 27 WO 2008/104562 PCT/EP2008/052367 tightening position, said radial anti-rotational tooth or teeth beingn engaged in corresponding recesses or nothces provided in the head side of the tightening ring nut, said teeth being provided beyond the end of 5 the threaded portion. Particularly anti-rotational teeth have a lower elastic deformability than projections for temporary positioning and retaining the ring nut in its partial screwed condition, while engaging recesses or nothces 10 of the ring nut can be the same cooperating both with temporary retaining projections and with anti rotational teeth. Moreover the body of the joint, on its outer shell surface, precisely on the side opposite to the threaded 15 one intended for screwing the ring nut, is provided with suitable fastening/anchoring means, generally represented by a further thread, which fastening means allow the joint to interact with other devices for example valves, or T or elbow joints, or still other 20 joints of the type previously described, and of the type commercially available in order to allow two final sections of pipes having different sections or composed of different material to be coupled. According to a further characteristc of the 25 present joint, the body thereof is internally made such to have at least two abutting shoulders of the pipe end having an inner diameter slightly smaller one with respect to the other. Due to this inner configuration of the body, the same joint can be used for pipes 30 having different diameters without changing neither the 28 WO 2008/104562 PCT/EP2008/052367 sealing ring, nor the annular seal, since due to the characteristics of the joint that have been previously described, both the clamping ring, and the annular seal have the possibility to change, within material limits 5 allowed thereto, their inner port, thus to be adapated to clamp/retain also pipes having different diameters. Therefore unlike joints actually on the market the present joint has the possibility of being used not for only one pipe having a specific outer diameter, but is 10 can be used for at least two pipes having different outer diameters, even if slightly differing one from the other. These and other characteristics and advantages of the present invention will be more clear from the 15 following description of some embodiments shown in annexed drawings wherein: Fig.1 is a section view of an half of a joint with the clamping ring engaged in the joint in its condition not tightened on the pipe. 20 Fig.2 is the clamping ring engaged in the joint in its tightened condition on the pipe. Figs. 3 and 4 are a side view of the clamping ring and a top view thereof respectively. Fig.5 is a detail of the clamping ring. 25 Fig.6 particularly is the position of the annular seal of the O-ring type or the like with the joint in its not tightened condition. Fig.7 is a detail of the position of the annular seal of the O-ring type or the like with the joint 30 tightened on the pipe. 29 WO 2008/104562 PCT/EP2008/052367 Fig.8 particularly is the position of the lip seal with the pipe not inserted in the joint. Fig. 9 is the position of the lip seal with the pipe in the inserted condition wherein the joint is not 5 tightened on the pipe. Fig. 10 particularly is the position of the lip seal with the joint tightened on the pipe. Fig.11 is a section view according to a diametral plane of an alternative embodiment of the joint and 10 with the pipe in the withdrawn condition . Fig.12 is a section view of the joint of Fig.11 wherein the pipe is in a first partial position inside the joint, the ring nut and the clamping ring being already assembled on the joint body with the ring nut 15 screwed on the joint body wherein said ring is completely open and said condition of the pipe and joint corresponding also to a condition with the pipe partially withdrawn from the joint. Fig.13 is a section view like fig.12 and wherein 20 the pipe and the joint are in a second position wherein the pipe is completely inserted into the joint body and the ring nut is only partially rotated such to cause the ring to be in the initial tightening condition on the pipe. 25 Fig.14 like figures 12 and 13 is the pipe and the joint in a third position, wherein the ring nut is completely screwed on the joint till the ring nut completely abuts against limit stops means provided on the joint body. 30 Fig. 15 is a view like previous figures with the 30 WO 2008/104562 PCT/EP2008/052367 joint and the pipe in a fourth condition wherein the pipe is moved in the withdrawing direction with respect to the complete introduction position into the joint body because of hydraulic pressure or a pulling action 5 exerted on the joint, while the clamping ring by the portion having an abrupter inclination with respect to the axis of the pipe cooperates with the corresponding portion of the ring nut having a correspondingly abrupter inclination with respect to the axis of the 10 pipe and while the O-ring seal is more wedged between the outer wall of the pipe and a portion of the seat conically narrowing in the withdrawing direction of the pipe from the joint body. Fig.16 is an enlarged detail of the seal seat with 15 the seal in the position of figure 15. Fig.17 is a perspective view of the sleeve forming the joint body and wherein limit stop abutment means provided on the joint body and means for temporary stopping the free rotation of the ring nut on the 20 thread of the joint body by a frictional locking action can be seen. The body of the joint has a union 101 for coupling the pipe 5 having an outer thread 201. The union 101 has an inner shoulder 301 being a radial abutment 25 surface for an annular seal 11 of the O-ring type. The inner annular shoulder 301 is also a side wall of a seat housing said annular seal in the form of a groove made in the inner surface of the coupling union 101. The pipe is retained in place by a clamping ring 2 30 by an intrinsic elastic force firmly keeping it under a 31 WO 2008/104562 PCT/EP2008/052367 condition wherein its inner diameter is slightly greater than the outer diameter of the pipe 5, in its resting condition, i.e. with the pipe not tightened into the joint. Therefore the pipe can be inserted into 5 the clamping ring 2 with no physical obstacles. The clamping ring 2 is tightened on the pipe by means of a tightening ring nut 4 whose inner thread can be screwed on the outer thread of the coupling union 101. 10 Particularly fig.1 shows the joint in its not tightened condition. Moreover, as it can be noted in fig.1, even if the clamping ring 2 is engaged in the body 1, however it has an inner diameter that is slightly greater than the 15 outer diameter of the pipe 5. The clamping ring has one or more crown of teeth 6. These teeth have no interaction with the pipe 5 when the joint is in its not tightened condition so that upon the introduction of the pipe 5, it is not subjected to any physical 20 impediments by the clamping ring 2. The clamping ring 2 has snapping means for the engagement by applying a slight external pressure in the body 1. Said means are composed of a projecting tooth 7 25 obtained on the outer shell surface of the clamping ring 2, which projecting tooth 7 engages in a suitable annular fitting groove 8 obtained on the inner surface of the body 1 by this arrangement. Said clamping ring 2 is firmly retained in the body 1 by a predetermined 30 retaining force, which is however greater than the 32 WO 2008/104562 PCT/EP2008/052367 force generated by possible slipping actions when the pipe 5 is taken out from the joint, so the ring 2 can be disengaged by the body 1 only by means of an external operation made by the user, i.e. by a simple 5 manual action. Moreover it is to be noted that after the introduction in the body 1 of the clamping ring 2 it is slightly circumferentially, elastically deformed, in its side engaged in said body 1. Such deformation 10 elastically reduces, at a certain extent the diameter of the clamping ring at its head end inside the body of the joint and so due to the particular configuration of the clamping ring it results in that said clamping ring 2 takes a substantially conical condition, i.e. with 15 axial clamping tongues slightly inclined, arising a flower petal-like shape, that is, axial tongues slighlty outwardly open with respect to the central axis of the joint. When the pipe is tightened in the joint the ring nut radially compresses the clamping 20 tongues at the end thereof outside the joint so that they are radially inwardly inclined against the wall of the pipe. In figures the double arrow F points out this functionality or this behaviour of the clamping ring. Still in fig.1 it is clear that the external shell 25 surface of the clamping ring 2 at the ring end intended for the elastic interaction with the ring nut 4, has a wedge-shaped or conical surface 102 that, during the step screwing the ring nut 4, just cooperates with an inner conical surface portion 104 of the ring nut 4. 30 Fig.2 shows the joint in its tightened condition. 33 WO 2008/104562 PCT/EP2008/052367 As it is clear that, after the ring nut 4 has been screwed on the body 1, the wedge-shaped or conical surface 102 of the clamping ring 2 interacts with the inner conical surface 104 of the ring nut 4, so the 5 clamping ring 2 is elastically deformed according to the arrow F narrowing the inner port delimited by the ring. It is noted that with the joint in its tightened condition, the inner diameter of the clamping ring 2, particularly the inner diameter of the port delimited 10 by the crowns of teeth 6 of the ring 2, is smaller than the outer diameter of the pipe 5 so said teeth 6 grip the outer surface of said pipe 5 allowing the ring 2 to firmly clamp said pipe 5 in the joint. In addition to the fact of being elastically 15 deformed narrowing its inner port, the clamping ring 2, contemporaneously to the above mentioned action, is subjected to an axial movement towards the inside of the body 1, still due to the ring nut 4 being screwed on said body. As it is easy to guess, by screwing the 20 ring nut 4 on the body 1 an axial movement of the ring nut 4 towards the body 1 occurs. Since the inner conical surface of the ring nut 4 interacts with the wedge-shaped or conical surface of the ring 2, it results that upon an axial movement of the ring nut 4 25 after it has been screwed on the body 1 a movement of the ring 2 occurs in the same direction. The annular groove 8, has a certain axial extension and the tooth 7 of the clamping ring 2 can move, during the axial movement, towards the seal, by 30 means of a suitable conicity of the annular fitting 34 WO 2008/104562 PCT/EP2008/052367 groove 8. Obviously by bringing the joint from a tightened condition to a not tightened condition, that is by unscrewing the ring nut 4 from the body 1, the ring 2 5 by means of its firm maintenance intrinsic elastic force, spontaneously recovers a condition wherein inner diameters of peaks of the crowns of teeth are again slightly greater than the outer diameter of the pipe 5, allowing the pipe 5 to be taken out from the body 1 10 without any impediments. Moreover the ring 2 recovers its initial axial position without the risk of being disengaged from the body 1 due to possible slipping actions of the pipe when it is taken out from it, since, as previously said, the fitting coupling force 15 of the ring 2 on the body 1 obtained by the peripherical annular projection and by the fitting groove in the body 1, is anyway greater than the force generated by said possible slipping actions of the pipe when it is taken out. 20 Fig.3 shows a side view relating to a preferred solution used for the clamping ring 2. As it can be easily noted it has two axial slots 9 and 10 that are opposite and open alternatively on one of the two opposite head sides. These slots creates, for the 25 external shell surface of the ring 2, a shape of the plane development of the shell surface (not reppresented in fig.3) resembling a linked series of letters S. Said axial slots allow the clamping ring 2 to be elastically deformed with the joint in the 30 tightened condition. 35 WO 2008/104562 PCT/EP2008/052367 Particularly, axial slots 9 allow the crowns of teeth 6 on the head side of the ring intended to interact with the ring nut 4, to be tightened by a radial restriction under the narrowing action caused by 5 ring nut 4 screwed on the body 1, while axial slots 10 on the head side opposite to the above mentioned head side, allow the ring 2 to be deformed just enough to be inserted in the body 1 and to allow the fitting tooth 7 of the ring 2 to be engaged by a snapping action in the 10 suitable fitting groove 8 obtained on the inner surface of the body 1 and therefore to allow the ring 2 to take a shape resembling flower petals. Fig.4 shows a top view of the clamping ring 2 through which it is possible to see the spatial 15 arrangement of the two axial slots 9 and 10. As it is noted, they are staggered one with respect to the other with a given constant angle. Obviously the amount of axial slots 9 and 10 can be changed for example depending on the size of the 20 outer diameter of the pipe 5 to which the clamping ring 2 has to be applied. By changing the amount of said exial slots 9 and 10 as a consequence even the angle comprised between two consecutive slots 9 and 10 changes. 25 Fig.1 and fig.5 show a detail of the clamping ring 2 which has an intrinsic elastic force for firmly maintaining a condition such that its inner diameter is slightly greater than the outer diameter of the pipe 5 so it can be inserted in the ring without any 30 mechanical and/or excessive friction impediments even 36 WO 2008/104562 PCT/EP2008/052367 in the engaging condition of fig.1. Moreover it can be noted that peaks of teeth 6 forming the crowns of teeth of the ring 2, lie on concentric circumferences which have diameters that are 5 progressively reduced in their value from the outermost crown of teeth 6 to the innermost one. Fig.6 shows a section plane/cross section of the joint according to a first embodiment, wherein particularly the position of the annular seal such as 10 0-ring or the like 11 can be noted being inserted inside the body 1, with the joint in its not tightened condition. As it appears evident in this variant the seat of said annular seal 11 is composed of a conical narrowing 15 characterized by a first slightly conical portion 103 and a second portion 203 being more conical with respect to the preceiding portion, which conical narrowing extends in the side opposite to the end of the joint for introducing the pipe by a third conical 20 narrowing 303 being slightly conical and whose length is approximately equal to the size of the diameter of the longitudinal section of the seal 11. Said terminal portion 303 of the above conical narrowing, constitutes actually the seat of the annular seal 11 with the joint 25 tightened on the pipe 5. The annular seal 11 in its rest condition, i.e. with the joint not in its not tightened condition, has an inner diameter greater than the outer diameter of the pipe 5 and for this reason, as it is shown in 30 figure 6, after said seal 11 has been inserted in the 37 WO 2008/104562 PCT/EP2008/052367 body 1 it is housed in the first conical narrowing portion 103 having said greater diameter and such to keep the seal in the largest radially condition and so allowing the pipe 5 not to have any mechanical and/or 5 excessive friction impediments when it is inserted in the joint. From the figure it is clear that the head side of the clamping ring 2, i.e. the side thereof engaging the fitting annular groove 8 in the body 1 by the 10 projecting annular projection 7, with the joint in its not tightened condition, is immediately near to the annular seal, however without leading to any pushing axial actions thereon. Figure 7 shows the position of the annular seal 11 15 with the joint tightened on the pipe 5. Said seal, in comparison with the previous fig. 6, is axially moved towards the bottom of the seat of the seal and wherein there is provided the slightly narrowed conical portion having the smallest diameter among various diameters of 20 the seat of the seal and however it is such to determine an inner radial compression of the annular seal against the pipe. Said movement of the seal 11 is caused by the pushing action made by suitable pushing means which, 25 according to a specific technical solution, are represented by the clamping ring 2 and the ring nut 4. As previously described, when the joint is tightened, following the ring nut 4 screwed on the body 1, the clamping ring 2, is axially pushed towards the 30 inside of the body 1 and such movement causes the ring 38 WO 2008/104562 PCT/EP2008/052367 2 to interact with the seal 11 pushing it towards the final portion of the conical narrowing having the smallest diameter, thus forcing it between the outer wall of the pipe 5 and the wall of said conical 5 narrowing. After said movement and forcing action, the seal is subjected to an elastic deformation radially narrowing it, so, as it can be noted in fig.7, the inner diameter of the seal 11 is smaller than the outer 10 diameter of the pipe 5 and such condition allows said seal 11 to adhere against the outer wall of the pipe 5 thus guaranteeing the desired hydraulic sealing effect. By passing from said tightened condition of the joint, to a joint in its not tightened condition, i.e. 15 by unscrewing the ring nut 4 from the body 1, the clamping ring 2 spontaneously comes back to the original axial position such as previously shown in fig.6. Such spontaneous returning action is due to the intrinsic elastic firm maintenance force of the ring, 20 by means of which the ring 2 tends to return back to its not stressed firm condition, i.e. it tends to become wideer according to the arrow F causing its inner diameter to be greater than the outer diameter of the pipe 5. At the same time such widening of the ring 25 2 is followed by the axial movement thereof, towards the entrance end of the joint, since upon the widening of the ring 2 the projecting tooth 7 slides on the inner wall of the conical narrowing and such sliding action is not blocked since it occurs from the side of 30 the conical narrowing having the smallest diameter, to 39 WO 2008/104562 PCT/EP2008/052367 the side thereof having the greatest diameter. In other words, the shape memory of the clamping ring 2, allows it to elastically return back to its original not stressed shape when the compression due to 5 the ring nut 4 has been removed, since the deformation circumferentially tightening the ring 2 due to the compression of the ring nut 4 is an elastic deformation and so, it does not lead to any considerable plastic deformation i.e. permanent deformation of the ring. 10 Therefore the ring 2 by recovering its original shape, i.e. by becoming wider, causes the final portion of said ring 2, represented by the projecting annular tooth 7, to slide on the wall of the conical narrowing inside the body 1 thus leading the ring 2 to axially 15 move towards the entrance of the joint. Obviously such axial movement of the ring 2 stops when the projecting tooth 7 begins to interact with the fitting annular groove 8. After such axial movement, the ring 2 is not more 20 in interaction with the seal 11 that can elastically return back to its initial position inside the body 1, i.e. on the side of the conical narrowing having the greatest diameter. Such movement can occur either spontaneously or at least partially by means of the 25 pipe 5 being drawn when it is taken out from the joint and said movement is made easier by the slight conicity of the portion 303 i.e. of the sealing seat. Figures 11 to 16 show a variant embodiment wherein according to a first advantageous characteristic, said 30 coupling union 101 has an inner radial narrowing 401 40 WO 2008/104562 PCT/EP2008/052367 composed of two opposed conical surfaces 501, 601. One of which substantially arising from the annular, radial shoulder 301 towards the opposite end of the coupling union 101 that is in the withdrawing direction of the 5 pipe 5, and which conical surface 601 converges towards the inside of the pipe, and at the narrowing 401 it is connected to a conical surface 501 diverging towards the end of the coupling union faced in the direction for withdrawing the pipe 5 from the joint. 10 The clamping ring 2 and the tightening ring nut 4 cooperate one with the other by means of mutually interaction conical surfaces provided at inner and outer head ends of the ring nut 4 and clamping ring 2 respectively, which head ends are at the opposite side 15 of said two parts with respect to the coupling union 101. At said end opposite to the coupling union 101 the clamping ring has two subsequent conical surface portions denoted by 102, 102', which have a different 20 conicity and are connected by a rounded or beveled arcuate portion 202. The first conical surface end portion has a greater inclination than the one of the second conical surface portion. The term inclination refers to the angle between an axial straight line 25 tangent to the conical surface and the pipe axis, of the ring nut 4 and/or of the clamping ring 2. Such term substantially is like the term conicity which in this document refers to the opening angle of the cone. The inner conical surface of the ring nut 4 is 30 also composed of a first and a second portion denoted 41 WO 2008/104562 PCT/EP2008/052367 by 104 and 104' and which inner conical surface portions of the ring nut 4 like conical surface portions of the clamping ring 2 have two different inclinations and particularly the first end portion 104 5 has a greater inclination than the second conical surface portion 104' being less inclined. According to an alternative definition first conical surface portions 102 and 104 of the clamping ring 2 and of the tightening ring nut 4 respectively 10 are abrupter than second conical surface portions 102' and 104' of corresponding parts, i.e. of the clamping ring 2 and of the tightening ring nut 4. Particularly, by not exclusively in the shown embodiment the second conical surface portions 102' and 15 104' of the clamping ring and of the tightening ring nut 4 have the same inclination, for example 30*, and are intended for sliding one upon the other when the tightening ring nut 4 is screwed for being tightened on the coupling union 101 and against the clamping ring 2. 20 The first two portions 102 and 104 on the contrary are more inclined, for example 50*. Particularly the first conical surface portion 102 of the clamping ring 2 has a greater inclination than the corresponding first conical surface portion 104 of the tightening ring nut 25 4. By means of the above arrangement upon the screwing of the ring nut, firstly the clamping ring 2 is axially compressed against the pipe 5 allowing inner teeth 6 of the clamping ring 2 to go inside the wall of 30 the pipe 5, that is to grip said wall. All this without 42 WO 2008/104562 PCT/EP2008/052367 requiring an excessive effort that can be manually applied, at least for pipes with diameters up to D40 or D50, without using tools for grasping the ring nut and anyway until the ring nut clearly abuts on the body, 5 while in the case of heavy pressures the necessary further tightening action occurs when the clamping ring pushed by the pressure cooperates with the first conical surface portion 104 with the first arcuate surface portion 202 of the clamping ring 2 and along 10 additional portions of such arcuate surface. The fact that said two surfaces are very abrupt causes the clamping ring to be tightened by a greater radial pushing action with a shorter axial travel of the pipe and of rotating sealing tools of the ring nut. 15 Therefore during the tightening action a lighter effort will be necessary. The additional tightening action will be necessary with heavy operating pressures of the plant, while an initial long travel is reduced to the passage of the two operating cooperating conditions of 20 the two second conical and curved surface portions and the two conical surface portions of the ring nut and clamping ring 2 respectively. The arcuate or beveled portion 202 connecting the first and second conical surface portion 102 and 102' 25 allows a passage free from resistances of above mentioned operating conditions to be provided, since during the passage between the two conicities the arcuate portion causes the clamping ring to have always only one tangent point against the profile of the angle 30 area between the two conical surface portions 104 and 43 WO 2008/104562 PCT/EP2008/052367 104' of the ring nut. Therefore a passage without resistence peaks occurs. From a quantitative point of view the first conical surface portion of the ring nut and/or of the 5 clamping ring has an inclination with respect to the central axis of the pipe and/or tightening ring nut and/or clamping ring greater than 30* and lower than 80*, and preferably it is from 40* to 60*, particularly from 45* to 50*. 10 As regards the second conical surface portion of the ring nut 4 and of the clamping ring 2, it has an inclination lower than 40*, preferably lower than 30* and particularly from 10* to 30*. The shown pipe joint is of the type wherein, the 15 pipe can be inserted and withdrawn from the joint with the seal, clamping ring 2 tightening ring nut 4 assembled on and/or into the coupling union 101. In this case with the tightening ring nut 4 partially screwed, the clamping ring 2 and the O-ring seal 11 20 have such an inner diameter that the pipe can slide into said parts with a frictional resistence against sliding that can be overcome by a manually applied force and without any excessive effort and without mechanically damaging the pipe and/or said two parts 2 25 and 11. As described above, upon the screwing of the ring nut, inner conical surfaces 104, 104' of the ring nut abut against outer surfaces of the clamping ring 2 and act for circumferentially pressing the clamping ring. 30 With reference to the seal 11 it can be provided 44 WO 2008/104562 PCT/EP2008/052367 with such a diameter that even with the ring nut partially screwed it has an inner diameter shorter than the pipe diameter to such an extent that the head side of the pipe upon introduction into the coupling union 5 101 elastically expands the seal 11 which is prevented from sliding in the introduction direction by the annular shoulder. In the withdrawing direction the seal 11 is prevented from sliding by the head wall of the clamping ring 2 denoted by 302. The inner diameter of 10 the seal can be such that it is shorter than the outer diameter of the pipe for an amount lower than or similar to 1 to 2,4 mm, in proportion to the size of the joint and to the chord of the O-ring. With the joint in its tightened condition, i.e. 15 with the ring nut completely screwed only the clamping ring 2 is compressed against the pipe. If the fluid increases its pressure, the sealing effect is guarateed by the fact that both the pipe and the seal are pushed in the withdrawing direction of the 20 pipe by the fluid so the seal 11 is wedged between the narrowing conical surface 601 and the outer wall of the pipe 5 with a greater strenght. Said functionality and arrangement is schematically shown in figures 11 to 16. Firstly the 25 tightening ring nut is only partially screwed on the coupling union 101, so the clamping ring 2 is not compressed against the pipe 5 and it can slide inside said clamping ring 2. However the seal 11 housed in the annular widening groove has a diameter shorter than the 30 outer diameter of the pipe 5. The inner diameter of the 45 WO 2008/104562 PCT/EP2008/052367 seal 11 is shorter than the outer diameter of the pipe for an interaction value changing from 0,5 to 1,2 mm in proportion to the size of the joint and the chord of the O-ring. 5 The groove housing the seal 11 is composed of a radial portion wider than the area with shortest diameter of the coupling union 101 from 0,1 to 0,5 mm, particularly 0,2 mm to 0,4 mm, in proportion to the size of the joint and the chord of the O-ring. 10 Upon insertion of the pipe 5 the latter expands the seal 11 and passes therein by a certain friction that due to said differences between the inner diameter of the seal and the outer diameter of the pipe is adjusted such that the friction of the pipe sliding 15 inside the seal can be overcome by means of a manual force applied by a user and without using tools, at least considering a predetermined diameter range of the pipe. Finally by tightening the ring nut the pipe is 20 clamped into the joint, Figure 12 to 14. In figure 15 a heavy pressure of the fluid pushes the pipe in the withdrawing direction SF and the seal 11 is pushed in the withdrawing and wedging direction between the pipe and the conical surface 501. 25 On the contrary in a variant suggested for greater diameters it is possible for the seal to be compressed by the clamping ring that is by the head side 302 thereof causing the inner dimater to decrease. In such case with the ring nut 4 partially screwed on the 30 coupling union , the seal 11 can have an inner diameter 46 WO 2008/104562 PCT/EP2008/052367 slightly greater than or susbtantially equal to the outer one of the pipe. Fig. 8 shows a section plane/cross section of the joint 1 having inside the body 1 a lip seal 12, with 5 the joint 1 in its not tightened condition and with the pipe 5 (shown by the broken line) not inserted in said joint. It can be noted that the lip seal 12 is composed of a base ring 13 having an inner diameter slightly 10 greater than the outer diameter of the pipe and of an extension/lip 14, secured to an end of the inner surface of the base ring 13 in which the inner port delimited by said lip, has an inner diameter smaller than the outer diameter of the pipe. 15 Moreover it can be noted that the section of said lip seal 12, or better to say the section of the base ring 13 of said seal 12 resembles to a right-angled trapezium whose oblique side has such an inclination to be complementary to the inclination of the annular 20 abutting shoulder, which with the inner cylindrical wall of the body 1 constitutes the seat of said seal 12. In fig. 8 the clamping ring 2 is further shown, which, as it can be seen, do not interact with the lip 25 seal 12 with the joint in its not tightened condition. Fig. 9 shows a section plane/cross section of the joint 1 having inside the body 1 a lip seal 12, with the joint 1 in its not tightened condition and with the pipe 5 inserted in said joint. 30 As it can be noted the lip 14 of the seal 12 47 WO 2008/104562 PCT/EP2008/052367 cooperates with the outer surface of the pipe 5 when it is introduced in the joint but only by a slipping action by the inner surface 15 of said lip 14 without preventing to easily take out the sealing body, 5 therefore even by using lip seals of the type described hereinbefore, the pipe can be freely introduced in the joint without any mechanical and/or excessive frition impediments. Moreover as it can be noticed, after having 10 inserted the pipe 5 in the joint, the outer surface 16 of the lip 14 comes to overlap the inner surface of the base ring 13 thus arising a space 17 having a wedge shaped cross section. Fig. 10 shows a section plane/cross section of the 15 joint 1 having a lip seal 12 inside the body 1, with the joint tightened on the pipe 5. After the ring nut 4 has been screwed on the body 3 the clamping ring 2, such as previously described, not only is circumferentially tightened against the 20 outer wall of the pipe 5 according to the arrow F, but it is also subjected to an axial movement towards the inside of the body 1 and such movement causes said clamping ring together with the ring nut to act as a pushing means against the annular lip seal 12. 25 Due to said axial movement of the clamping ring 2, the seal 12 is pushed against the annular abutting shoulder and following said pushing action the seal 12 is circumeferentially widened. More precisely, the annular abutting shoulder 30 being slightly inclined, a kind of compression of seal 48 WO 2008/104562 PCT/EP2008/052367 12 occurs therefore it results that the base ring 13 of said seal 12 is subejcted to the deformation, and such deformation results in the inner surface of the base ring to be circumferentially widened. 5 After said circumferential widening, the inner surface of the base ring 13 pushes against the outer surface 16 of the lip 14 pushing/forcing the inner surface 15 of the lip 14 to tightly adhere against the outer surface of the pipe 5. 10 In the operating condition of the joint, i.e. with the joint in its tightened condition on the pipe 5 and with the fluid passing in the pipe, the circular space 17 having a wedge-shaped section is flooded by the fluid which exters a pressure on the outer surface 16 15 of the lip 14, which pressure pushes the inner surface 15 of said lip 14 towards the outer surface of the pipe 5 thus cooperating with the pushing action of the base ring 13 following the elastic deformation thereof. Obviously the pushing action of the fluid against 20 the outer surface 16 of the lip 14 of the seal 12 is substantially directly proportional to the pressure of the fluid inside the pipe, so by increasing the pressure, as a consequence the hudraulic sealing effect of the seal 12 increases. 25 When the joint is released from the pipe, as previously said, the clamping ring 2 spontaneously recovers its original position, such as shown in fig.9 and consequently, the lip seal can elastically recover its initial/original shape under not stressed 30 conditions, either in a spontaneous way or also at 49 WO 2008/104562 PCT/EP2008/052367 least partially by the pipe being drawn when it is taken out from the joint. With reference to shown and described examples and to possible variants, the invention allows to leave the 5 joint in its ready condition to insert the pipe, with the seal housed in the seat and with the pipe freely moving inside it; the clamping ring already fitted in its seat and in its opened condition like a flower allowing the pipe to freely slide inside it and with 10 the ring nut screwed on the body of the joint with the conical face abutting against the conical face of the clamping ring at the beginning of the predetermined screwing travel necessary for mechanically clamping the pipe and the desired hydraulic tight seal. Therefore 15 the user has only to insert the pipe in the joint and so to tighten the joint by a simple rotation of the ring nut that is of minimum extent and that can be indicated by a reference between the body and the ring nut. 20 Advantageously in order to identify more easily the proper position for partially screwing the tightening ring nut 4 on the coupling union 101, with the clamping ring 2 and seal 11 allowing at least to introduce and/or also to withdraw the pipe from the 25 joint said parts being in the assembled condition, the invention provides a radial projection 701 or two or more radial projections in the trajectory at one peak of a thread 201 of the coupling union 101 arising from said area in the trajectory of the peak of said thread 30 201 and which projection or projections are engaged 50 WO 2008/104562 PCT/EP2008/052367 into a corresponding notch or recess or in a crown of notches or recesses 204 provided at the head side of the tightening ring nut 4 faced towards the coupling union 101 that is in the front with reference to the 5 direction for introducing the pipe 5 into the joint or screwing said tightening ring nut 4. Said notches or recesses 204 are open both at the head side and at the inner surface of said end of the tightening ring nut 4. Radial projections 701 at the bottom of the thread 10 201 can be elastically deformed and have such a protrusion to project with a slight interaction inside grooves 304 between threads 404 of the tightening ring nut 4, and to project more beyond the radial inner edge 504 of front recesses 204. Upon screwing, therefore, 15 interactions between projections 701 and front recesses 204 occur causing the ring nut 4 to move forward by steps which can be easily manually overcome, by holding it in the partial screwing position with respect to the coupling union 101. By further rotationally screwing 20 the tightening ring nut 4, projections 701 are elastically deformed and come out from front recesses 204 passing inside the groove 304 of the thread where there is some friction obtained by the slight interaction between the projection or projections 701 25 and the groove 201 preventing the ring nut from freely rotating holding its predetermined preassembly position. Therefore the action provides to temporary hold the ring nut in a predetermined screwing position. 30 Particularly the thread 201 on the coupling union 101 51 WO 2008/104562 PCT/EP2008/052367 is provided in an axial position of said coupling union 101 corresponding to a partial screwing position of the tightening ring nut 4 wherein the clamping ring 2 and the seal 11 allow the pipe to be inserted and/or in 5 case withdrawn by sliding inside the clamping ring 2 and the seal 11. So the tightening ring nut 4 is temporary effectively retained in its starting position which can be overcome by a simple manual effort. Particularly it has to be noted that the tightening 10 ring nut 4 and the clamping ring 2 manufactured with two conical portions denoted by 102, 102' and 104', 104' respectively cause the choice of the readiness position with the ring nut temporary retained in the partial screwing position (preassembly) on the coupling 15 union 101 to be such that the rotation necessary to completely tighten the ring nut 4 in order to sealingly clamp the joint on the pipe is very small, approximately from half a turn to one complete turn of the ring nut, so the joint is tightened on the pipe by 20 a very light effort and by a very simple and quick movement. Still according to a further advantageous characteristic, there are provided limit stop means for the screwing tightening travel of tightening ring nut 4 25 on the pipe preventing also the tightening ring nut 4 from being unintentionally rotated. Said means advantageously are composed of a radial tooth 801 or two radial teeth or a crown of more radial teeth. Such radial tooth or teeth 801 are provided on 30 the coupling union 101 in an axial position with 52 WO 2008/104562 PCT/EP2008/052367 respect to the axial position of the tightening ring nut 4 being screwed on said coupling union 101 corresponding to the joint being completely tightened on the pipe 5, so when the ring nut reaches said axial 5 position the radial tooth or teeth of the ring nut 204 engage into corresponding front recess or recesses 204 of the tightening ring nut 4. This can be obtained by means of the elasticity of radial teeth 801 that can be also the intrinsic elasticity of the material itself. 10 Under such condition, the rotation of the tightening ring nut 4 unscrewing and so opening the joint needs a certain force to be overcome for disengaging radial tooth or teeth 801 from front recess or recesses 204 of the ring nut, so effectively it is not possible to 15 unintentionally loosen or unscrew the tightening ring nut 4. Moreover the correct condition for screwing the tightening ring nut 4 corresponding to the correct condition for tightening the joint on the pipe is indicated to the user. All this leads to the fact that 20 upon the tightening action, the ring nut is prevented from being uselessly screwed too much by leaving to possible high pressures or pulling actions exerted on the plant a further automatic/dynamic sliding action of the seal pipe and clamping ring assembly on conical 25 surfaces of the ring nut, allowing high pressures of the fluid to be used in order to increase both the clamping condition and the sealing effect under such pressure conditions. The radial tooth or teeth 801 are composed of 30 radial axially oriented ribs having such a 53 WO 2008/104562 PCT/EP2008/052367 circumferential thickness which thickness is lower than the corresponding size of front recess or recesses 204 of the ring nut. With reference to a further characteristic, the 5 limit stop for the introduction of the pipe denoted by 901 in figures can be omitted and the body 1 of the joint can have an inner diameter that is always slightly greater than the pipe diameter. So together with the characteristic for introducing and withdrawing 10 the pipe into the joint without too much friction a repair joint can be obtained that is a joint particularly suitable for making repairs. The longer joint body 1 free from inner annular abutment shoulder 901 of the pipe allows the joint to slide inside the 15 pipe to be repaired, without the need of disassembling ring nuts and clamping rings from the body 1 and so making repair actions considerably more easier. 54

Claims (20)

1. Joint for connecting pipes composed of a body provided at least at an end with an outer thread; a cylindrical seat for inserting the pipe inside said body; 5 a ring nut intended to be screwed at the end of said body on the thread, said ring nut being provided with an inner conical surface; at least a clamping ring with an outer shell surface that is at least partially conical and intended to cooperate with the 'inner conical surface of 10 said ring nut and which ring internally has teeth intended to grip the end of the pipe inserted in the joint and said ring having the possibility of being tightened by means of a radial restriction caused by the ring nut being screwed on the body, 15 wherein said clamping ring has an intrinsic elastic force for firmly maintaining a condition wherein its inner diameter is slightly greater than the outer diameter of the pipe so that the latter can be inserted by an axial sliding action without any impediments in the clamping ring, and 20 said clamping ring can be elastically deformed narrowing the inner port delimited by the ring, against the action of said elastic force in a condition with the diameter reduced with respect to the diameter in its resting condition, at such an extent that teeth of the ring grip the outer wall 25 of the pipe by firmly clamping it inside the joint, said reduction being generated by the action of the conical surface of the ring nut on the conical surface of the clamping ring during the screwing action, wherein the clamping ring, has a projecting annular 30 tooth intended to elastically interact with the annular fitting groove obtained in the cylindrical wall of the seat.

2. Joint according to claim 1, wherein the clamping ring has two crowns of axial slots that are opposite and 35 open alternatively on one of the two opposite head sides, so to give the plane development of the shell surface of 55 the clamping ring a shape that can substantially resemble a linked series of letters S.

3. Joint according to any one of claims 1 and 2, wherein the clamping ring has at least a crown of 5 separating axial slots such to form a crown of axial tongues retained on a material continuous annular support and such tongues can be circumferentially compressed against the outer surface of the pipe, said slots being open only at one of the head sides of the ring. 10

4. Joint according to any one of claims 1 to 3, wherein the clamping ring has one or more axial slots in one or more intermediate or median positions of tongues, with reference to the angular extension thereof.

5. Joint according to claim 4, wherein intermediate 15 slots are open on one head side opposite with respect to slots separating tongues one from the other.

6. Joint according to claim 5, wherein intermediate slots of clamping tongues open at the head side of the clamping ring faced towards the joint body are such to 20 determine a circumferential elastic deformation on the side of the clamping ring intended to be inserted in the body, the outer diameter of the ring in its resting condition being slightly greater than the inner diameter of a seat for inserting it in the body of the joint and such that the 25 ring is housed in said seat by slightly narrowing its diameter at the end inserted in said seat however the diameter of the seat being such that the inner diameter of the clamping ring when it is inserted in the seat of the joint is anyway slightly greater than the outer diameter of 30 the pipe, while the inner diameter of the clamping ring progressively becomes wider towards the end thereof cooperating with the tightening ring nut.

7. Joint according to any one or more of the preceding claims, wherein the body has an initial entrance region 35 having a diameter greater than the outer diameter of the pipe and in whose shell surface there is provided an 56 annular groove for fitting the annular tooth retaining the clamping ring, which tooth engages by snapping in said groove by retaining the clamping ring in a condition engaged in the body, with a predetermined retaining force 5 and such that the ring can be disengaged from the body by a manual action, while with the clamping ring engaged in the body, said ring has always an inner diameter greater than the outer diameter of the pipe so it allows the pipe to easily slide in the ring of the joint, the force coupling 10 the ring in the body being such that it is greater than the force generated by possible slipping effects of the pipe when it slides.

8. Joint according to claim 7, wherein said fitting groove has side surfaces composed of opposite conical 15 surfaces having an inclination of about 30*.

9. Joint according to any one or more of the preceding claims wherein the projecting annular tooth is located at the end of the clamping ring.

10. Joint according to any one or more of the 20 preceding claims, wherein the opposite end of the outer surface of the ring, i.e. the end intended to elastically interact with the ring nut, has a wedge-like or conical inclined surface, which wedge-like or conical surface has the same inclination or an inclination consistent with the 25 inner conical surface of the ring nut with which it interacts when it is screwed on the body.

11. Joint according to any one or more of the preceding claims, wherein the conical surface at the head end of the clamping ring facing towards the tightening ring 30 nut and the inner conical surface at the end of the tightening ring nut opposite to the threaded portion of the joint body, i.e. facing in the direction introducing the pipe into the joint, have two adjacent conical surface portions having a different inclination with reference to 35 the central axis of the pipe and/or tightening ring nut and/or clamping ring, a first portion of said conical 57 surface, at the end of the clamping ring and at the corresponding end of the tightening ring nut, having an inclination (with respect to said central axis of the pipe and/or ring nut and/or clamping ring) that is greater than 5 the inclination of a second conical surface portion to which said first conical surface portion is connected in the direction of the threaded portion of the joint body, i.e. in the direction for introducing the pipe into the joint. 10

12. Joint according to claim 11, wherein the inclination of the second conical surface portion of the tightening ring nut is preferably 2-3 degrees greater than the inclination of the second conical surface portion of the clamping ring. 15

13. Joint according to claim 11 or 12, wherein the inclination of the first conical surface portion of the tightening ring nut is different from and slightly lower than the inclination of the first conical surface portion of the clamping ring. 20

14. Joint according to any one or more of the preceding claims 11 to 13, wherein on the clamping ring, the first conical surface portion is connected to the second conical surface portion by a rounded or beveled arcuate portion, while in the tightening ring nut the two 25 first and second conical surface portions are connected by an angle .

15. Joint according to claim 14, wherein the arcuate or beveled portion has such a curvature that in the passage along the angled area between the first and the second 30 conical surface portion of the tightening ring nut said arcuate or beveled portion of the clamping ring adheres against surfaces of the tightening ring nut only along one or two tangent lines by its possible narrowing positions

16. Joint according to any one or more of the 35 preceding claims 11 to 15, wherein the first conical surface portion of the tightening ring nut and/or clamping 58 ring has an inclination with respect to the central axis of the pipe and/or tightening ring nut and/or clamping ring greater than 30* and lower than 800, and preferably it is from 40* to 60, particularly from 450 to 500. 5

17. Joint according to any one or more of the preceding claims 10 to 15, wherein the second conical surface portion of the tightening ring nut and/or clamping ring has an inclination lower than 400, preferably lower than 30* and particularly from 10' to 30* with the 10 corresponding inclination of the clamping ring equal to or preferably lower than the corresponding one of the ring nut.

18. Joint according to any one or more of the preceding claims, wherein the clamping ring on its inner 15 surface at the end intended to clamp the pipe in the joint, has one or more teeth that make one or more series of crowns of teeth.

19. Joint according to any one or more of the preceding claims, wherein peaks of teeth 20 making the one or more series of crowns of teeth of the clamping ring, preferably lie on two or more axially adjacent circumferences and said circumferences are concentric having such diameters that progressively reduce their own value from the outermost crown of teeth, i.e. 25 the one near the end of the clamping ring, to the innermost one.

20. Joint according to claim 19, wherein with the joint in its not tightened condition, and with the ring nut screwed on the body of the joint corresponding to the 30 initial angular position of the tightening travel i.e. when the pipe can still freely slide in the two directions, tongues of the clamping ring are inclined in a slightly opened condition like flower petals with such an inclination angle that peaks of clamping teeth that are 35 provided to be arranged on one or more crowns of teeth or constituting two or more circumferential teeth, which 59 crowns or which circumferential teeth extend each one on an inner circumference of the clamping ring having a different axial position, have different radial distances from the surface of the pipe increasing for crowns of 5 teeth or circumferential teeth provided on circumferences that are nearer the conical end of the clamping ring, such that circumferential teeth or teeth of crowns of teeth corresponding to circumferences with different axial positions progressively grip the outer surface of the 10 pipe, i.e. one after the other, upon the screwing of the ring nut starting from the innermost crown of teeth or circumferential teeth, i.e. near the seal and subsequently involving the crowns of teeth more distant from said seal. 60