Background art Several tube fittings of the above mentioned type are known which comprise, according to the precharacterising part of claim 1, at least a pair of tubular end elements, adapted for reciprocal coupling to fixedly secure the end portion of a tube by means of an elastic sealing member of substantially annular shape.

The tubular elements can be reciprocally connected by means of threaded couplings and have on their external sides polygonal nuts or other grip elements to exert a tightening couple during their reciprocal connection.

Tube fittings are known in which the sealing member is a packing, which is glued to the hose external surface by means of special adhesives so as to form a coupling and shoulder element for the hoses. The drawback of this type of fittings lies in the fact that in case the packing has to be replaced, it can be removed only by cutting the end portion of the hose and by fixing again with adhesives the new hose extremity. This solution, besides being

complex and laborious, causes a shortening of the tube length, which may in some cases be not acceptable.

Another type of fitting provides that a spigot is inserted inside the hose so that the latter is stiffened and a shoulder element is created to allow tightening of an external nut acting as a mechanically fixing element. In turn the external nut can cooperate with a tubular fitting element by inserting a packing.

This solution is rather effective but has the drawback that it reduces the internal hose diameter, which in some cases can seriously reduce the hose flow rate in an unacceptable way, especially of fluids under vacuum.

Moreover it is rather complex and excessively costly due to the number of components forming the fitting.

Another drawback of the known fittings is their little flexibility of use due to the fact that, for every hose diameter, it is necessary to have socket joints and packings of very precise diameter to avoid clearances and leakages. It is thus necessary to hold in stock a large number of spare parts.

Another disadvantage common to all known tube fittings is the limited operation life of the sealing elements which are usually made of plastic materials of relatively high hardness.

Description of the invention The main purpose of this invention is to eliminate the abovementioned disadvantages by means of a fitting for rigid or semi-rigid tubes, particularly for ribbed plastic hoses, that allows to create an optimal mechanical grip and hydraulic tightness.

A particular purpose is to make a fitting for various hoses that maintains its flow section unchanged with respect to that of the hose to be connected, Another purpose of the invention is to provide a fitting with high flexibility of use by being adaptable to various hose diameters to be connected without changing each time the sealing members.

Another important purpose of the invention is to provide a fitting of rather simple structure and with a minimum number of parts in order to increase the system reliability and reduce production and installation costs.

Another purpose of the invention is to provide a fitting for rigid or semirigid tubes re-usable several times without replacing the sealing members.

The above mentioned purposes and others which will be better clarified hereinafter are achieved by a fitting of the type as defined above, characterised in that said sealing member is elastically yieldable, has a convex external surface suitable to cooperate with portions of complementary shape of the surface of said tube elements and an internal surface suitable to cooperate with the external tube surface to exert both mechanical grip and hydraulic tightness.

Preferably, the convex external surface of the sealing member has at leas one substantially rounded portion.

By means of the rounded shape of the sealing member, the forces exerted on the latter by the tubular elements will be distributed in a substantially uniform manner in the elastic mass and directed towards the hose central axis, producing both a mechanical grip and hydraulic tightness with respect to the

tube.

Advantageously, the external rounded shape of the sealing member can be produced by the rotation of a curved line around the axis of that member.

Preferably said curved line is a portion of circle or ellipse or ellipsoid.

Moreover, the internal surface of the sealing member is substantially cylindrical.

Alternatively, the internal surface of said sealing element can be provided with ribs or grooves of substantially complementary shape with respect to spiral or circular irregularities made on the hose external surface to improve their reciprocal coupling.

Brief description of the drawings Further avantages and aspects of the invention will become more evident from the detailed description of preferred, non limitative, embodiments of a pipe fitting, hereafter shown by way of non-limitative example by means of the accompanying drawings, in which: Fig. 1 shows a section view of a fitting according to the invention along an axial plane; Fig. 2 shows a section view along plane ll-ll of the fitting of Fig. 1; Fig. 3 shows a section view along plane Ill-Ill of the fitting of Fig. 1; Fig. 4 shows an exploded section view of the fitting of Fig. 1; Fig. 5 shows an exploded axonometric view of the assembly of Fig. 4; Fig. 6 shows a section view of the fitting of Fig. 5 assemble on a spiral- shaped tube in three successive assembling steps a), b), c); Fig. 7 shows a section view of an alternative embodiment of the tube

according to the invention in three successive assembling steps a), b), c); Fig. Q shows a section view of a second embodiment of the fitting according to the invention assembled on a smooth-shaped tube, in three successive assembling steps a), b), c); Fig. shows a section view of a third embodiment of a fitting according to the invention sectioned along an axial plane; Fig. 10 shows a section view of the fitting of Fig. 9 along plane X-X.

Description of an embodiment With reference to the cited figures, there is shown a first embodiment of a fitting according to the invention, generally indicated 1, suitable to tighten a hose extremity 2 to another hose or to an appliance, like a pump or a nozzle, not shown in the figures.

Particularly, the fitting 1 comprises first 3 and second 4 tubular elements suitable to be coupled to each other by means of a third tubular element or central sleeve 5. To this end, the tubular elements 3,4 are provided with respective external threads 6,7 screwed on respective internal threads 8,9 of sleeve 5.

Alternatively, sleeve 5 instead of being separate from anyone of the elements 3 or 4 can be a unitary part of either of said elements 3 or 4.

Moreover, at least one of the first two tubular elements 3,4 and in particular the tubular element 3, can be provided with a threaded extremity portion 10 apt to connect it with another similar fitting or with an external appliance, like a nozzle, a pump delivery or suction orifice, not shown in the drawings.

Alternatively, the two tubular elements 3,4 can have the same shape and

face each other to fix together two adjacent hose sections.

The two tubular elements 3,4 are provided with an internal diameter D sufficiently large to fit one hose extremity 2, even with a rather big clearance, but not smaller than the hose internal diameter 0 so as not to reduce the flow section. In other words the hose 2 can have a variable external diameter and thickness within broad ranges for easy coupling to the fitting according the invention, thus reducing spare parts held in stock.

Finally, on the external surface of the tubular elements 3,4 there are provided polygonal irregularities 11,12 or of other shapes like knurling to ease the hold by means of tools.

The pipe 2 is held between the tubular elements 3,4,5 by interposing a yielding sealing member 13 of approximately annular shape.

According to the invention, the sealing member 13 has a rounded external surface S, i. e. of bulb shape, and is adapted to cooperate with the tubular elements 3,4 at their internal portions 14,15 which have a complementary shape with respect to the contact surface of member 13.

Consequently, by screwing the tubular elements 3,4 on the intermediate element 5, the portions 14,15 of the first two elements will exert compression forces on the sealing member 13 with a resultant force approximately directed towards the longitudinal axis V and more particularly towards 1 : he centre C of same member. In the portion of greatest diameter, the sealing member 13 engages the internal surface of the intermediate element 5 which, by reaction, produces a compression force directed towards the axis V of the tube 2,

It must be observed that the internal portion 14,15 of the end tubular elements 3,4 are provided with substantially annular grooves, with complementary shape to the sealing member facing portion 13.

Preferably the external rounded surface S of the sealing member 13 is obtained by rotation of a curved line around the axis V of said member 13.

Said curved line may be a circle portion, e. g. over an angular sector of about 90°, Thus, the sealing member 13 has approximately the shape of a bulb or sphere cut in the region of the polar bowls.

Alternatively, said curved line can be a section of ellipse or ellipsoid. The generatrix curve can also be of different shapes, provided it has rounded extremities.

Appropriately, the annular sealing element has an approximately cylindrical internal surface 16 to uniformly surround and tighten the external hose surface 2.

In case the external hose surface 2 has spiral ribs like in the case of corrugated flexible tubes for electrical installations, grooves or protuberances 17 of substantially complementary profile can be made on the internal wall 16 to produce both hydraulic tightness and mechanical grip on the external hose surface.

Thanks to the rounded shape of the member 13 external surface, the compressive forces produced by elements 3,4 joined together by element 5 will be distributed towards the inside of member 13 plastic mass with rather uniform yield.

Preferably, the sealing member 13 is made of a material with high elastic memory and Shore hardness comprised between 20 and 80 and preferably between 40 and 60.

The yielding material of which member 13 is made, can be chosen among synthetic or natural rubbers and preferably among the elastomeric foams with open or closed cells, e. g. polyuretanic or silicon foams, depending on the applications or performances of the fitting.

By choosing a rather yielding material, the sealing member can be adapted to various diameters that might also considerably vary, guaranteeing at the same time a high hydraulic tightness. Moreover, thanks to the material yieldability of the sealing member, it adapts its shape to possible external tube stiffening elements, thus further providing a high mechanical grip.

On the contrary, the tube elements 3,4,5 can be made of rather rigid materials, like for example plastic materials of the type PVC, PP, PTE, ABS or of metal that can be easily worked or formed, like all ordinary fittings.

Fig. 6 shows schematically the fitting of the above figures in the assembly phases ol a spiral-shaped hose 2, i. e. with smooth inside wall and spiral irregularities on the external surface.

In this case, the sealing member 13 has on its inside wall annular or helicoidal protrusion similar to those of tube 2, in order to increase mechanical grip and hydraulical tightness during screwing of elements 3,4 and 5 as shown in steps a), b), and c).

The embodiment of the fitting of fig. 7 differs from that of fig. 6 essentially in that the sealing member 14 has a substantially cylindrical and smooth inside

wall.

Steps a), b) and c) show that screwing of elements 3,4 and 5 produces progressive elastical yield on member 13 in such a way that its inside cylindrical wall 16 exactly fits to the hose external surface 2 and penetrates in the surface irregularities thus increasing mechanical grip and hydraulic tightness with respect to the hose itself.

Figure 8 shows the fitting of figure 7, assemble on a hose 2'with substantially smooth external surfaces.

In step a) the fitting is opened and tube 2'is simply inserted in diameter D, In step b) the tubular elements 3,4 are screwed on the central element 5 and start compression of member 13'.

In step c) tubular elements 3,4 and 5 are fully screwed, completely yielding member 13'exerting on the hose external surface both a strong mechanical grip and hydraulic tightness.

In the embodiment of the fitting shown in Fig. 9 the elements which are identical or equivalent to those of the former figures have been identifie with the same reference numbers followed, where necessary, by apices.

Similarly to the above described embodiments, the fitting 1'can be assemble on an extremity portion of a smooth hose 2'and is made by a first external or female tubular element 3', and by a second internal or male tubular element 4' reciprocally coupable by means of respective internal and external threads 6', 7',

The external tubular elements 3'can be provided with an end portion 10'for its connection to another tube or hose or to an appliance.

Obviously the diameters of the two elements are such that they allow to insert the inside or male element 4'into the outside or female element 3'.

Surface irregularities 11', 12'can be provided on the external surface of element 3', 4'to increase tightening tools hold or operators hand hold.

The sealing member 13'is provided with a convex external surface S'with a substantially rounded end portion 13"and a second tapered or conical end portion 13"'.

Its internal surface 16'can be essentially smooth to cooperate with the external surface of hose 2'.

Also in this case, the end tubular elements 3', 4'have respective internal portion 14', 15'of complementary shaped to sealing member portions 13", 13"'of the sealing member 13', Thus, after insertion of end portion of tube 2'inside the central cavity of the internal tubular element 4'and sealing member 13'in the inside cavity of the external fitting element 3', by screwing reciprocally the end elements 3', 4' the sealing member 13'ì elastically yields hose 2'by means of the respective portions 14', 15'of complementary shape.

Possibly, to improve the fitting assembly condition a sleeve18 can be provided of rigid material like brass to be inserted inside tube 2'to support it radially during compression of member 13'. Though the fitting according to the invention has been described in particular with reference to the figures, the invention can be subject to numerous modifications and variations, without thereby departing from the scope of the invention as defined in the following claims,