Prior art A number of embodiments of junction devices are known for connecting together multilayer pipes and threaded terminals of hydraulic plants or apparatus such as radiators or boilers. Particularly, a frequently used junction device includes a metal core which is integral with the terminal and is adapted to be introduced in a longitudinal end of the multilayer pipe, and an outer cylindrical portion adapted to enclose the same end of the pipe. The core generally has one or more external 0-rings, whereas the outer cylindrical portion is plastically deformed by compression upon mounting thereof, to fasten the pipe on the terminal.

An apparent drawback of this arrangement lies in that both the outer cylindrical portion of the joint device and the pipe end are plastically deformed, whereby the device may be hardly dismantled and no reuse thereof s possible once it has been removed. Furthermore, the pipe end is irremediably damaged and has to be cut out before joining it anew.

US-A-3980325 discloses a device for connecting the longitudinal end of a flexible pipe and an externally threaded terminal having a male. member adapted to be inserted

in the pipe. The device comprises a hollow nut designed to be tightened on the threaded terminal when the male member of the terminal is inserted in the pipe end. The nut also has an inner frusto-conical portion adapted to compress a collet against the end of the pipe to clamp the latter.

This arrangement is difficult to implement when the terminal and at least one layer of the pipe are made of metal, like in hydraulic and heating plants for buildings. In such cases, the metal layer of the pipe might easily come in contact with the terminal, thereby allowing the passage of stray currents, and leading to corrosion problems.

WO-A-9801695 and EP-A-1020675 disclose similar junction devices, each comprising an inner core, with the pipe end being slipped thereon, and an external nut, designed to be tightened on a threaded terminal. By means of a frusto- conical portion, the nut compresses an intermediate bushing against the outer wall of the pipe and against a peripheral edge of the terminal. More in detail, the intermediate bushing has a cylindrical portion designed to contact the outer wall of the pipe and a front portion designed to be interposed between the peripheral edge of the terminal and the pipe.

An apparent drawback of this arrangement lies in that the front portion of the intermediate bushing may be deformed or displaced due to the pressure exerted by the nut, thereby increasing the risk of electrical contact between a metal layer of the pipe, if any, and the terminal, and allowing the passage of stray currents.

Further embodiments are also known, similar to the above,

wherein both the intermediate bushing and the inner core are made of metal, to provide high rigidity and resistance to the junction device. In these cases, the peripheral edge of the pipe generally abuts against a plastic washer.

These arrangements have the drawback that the washer may be easily displaced and allow the electrical contact between the metal layer of the pipe and the other metal parts of the junction device.

Also, the inner core and/or the intermediate bushing have appropriate projections to facilitate pipe clamping. Due to the clamping pressure exerted by the nut, these projections permanently deform the pipe and prevent any reuse of its end.

Also, these projections may engrave the plastic surface layers of the pipe and come in contact with the metal layer thereof, thereby increasing the risk of stray currents and electro-corrosion.

A further drawback arises when the joint device has to be dismantled. In fact, the projections of the inner core can make it very difficult to remove the core from the pipe.

Summary of the invention A primary object of this invention is to obviate the above drawbacks, by providing a cost-effective fitting.

A particular object is to provide a fitting that can be reused several times and allow easy mounting/removal thereof.

An additional object of the invention is to provide a fitting that effectively prevents stray currents and is little prone

to electro-corrosion.

Another particular object is to provide a fitting that can assure a high sealing action and does not damage the pipes to be connected.

Yet a further object of the invention is to provide a sturdy fitting, whose features remain unchanged with time.

These objects, as well as others that will be more apparent hereafter, are achieved, according to claim 1, by providing a corrosion resistant fitting for multilayer pipes, particularly for connecting an at least partly threaded metal terminal to a multilayer pipe with at least one metal layer, comprising a substantially rigid hollow sleeve, to be inserted in an end of the pipe, a clamp member having an internally threaded portion to be tightened on said terminal, an elastic bushing interposed between the clamp element and the pipe to compress the latter against the hollow sleeve and/or against the terminal upon tightening of the clamp member, electric insulating means for preventing the passage of stray currents between the pipe and the terminal, characterized in that the electric insulating means include a gasket made of an electrically insulating base material, having an axial tubular portion to be interposed between the hollow sleeve and the inner surface of the end of the pipe, and a radial portion to be interposed between the terminal and the front edge of the end of the pipe, to jointly increase both the sealing action and the resistance against electro-corrosion.

By this particular arrangement, an effective fitting resistant against stray current and electro-corrosion may be

obtained, which can also provide a high hydraulic and mechanical sealing action.

Brief Description of the Drawings Further features and advantages of the invention will be more apparent from the detailed description of a few preferred, non-exclusive embodiments of a fitting according to the invention, which are described by way of non-limiting examples with the help of the annexed drawings, in which: FIG. 1 is a sectional and partially exploded view of a first embodiment of a fitting in accordance with the invention; FIGS. 2,3 and 4 are further views of the fitting of FIG. 1; FIG. 5 is a sectional and partially exploded view of a second embodiment of a fitting in accordance with the invention; FIGS. 6,7 and 8 are further views of the fitting of FIG. 5; FIGS. 9 and 10 are views of a detail of the fitting of FIG. 1; FIG. 11 is a view of a detail of the fitting of FIG. 5; FIG. 12 is a partial view of the fitting of FIG. 5; FIG. 13 is a partial view of the fitting of FIG. 1; FIGS. 14 and 15 are views of another detail of a fitting according to the invention; FIG. 16 is a view of a detail of the fitting of FIG. 5; FIG. 17 is a view of a detail of the fitting of FIG. 1; FIGS. 18 and 19 are views of another detail of a fitting according to the invention ; FIGS. 20 and 21 are partly sectional views of an embodiment of a detail of the fitting in accordance with the invention;

FIGS. 20'and 21'are enlarged views of the detail of FIGS. 20 and 21 respectively; FIG. 22 is a plan view of a detail of FIGS. 20 and 21; FIG. 23 is a sectional side view of a detail of FIGS. 20 and 21, as taken along a plane XXIII-XXIII.

Detailed description of a few preferred embodiments With particular reference to the above figures, a corrosion resistant fitting according to the invention is described, which is generally designated with numeral 1. Fitting 1 may be advantageously used for multilayer pipes and will be particularly effective for connecting one at least partly threaded metal terminal T to a multilayer pipe P. The latter may have at least one metal, e. g. aluminum layer, interposed between at least two plastic layers.

Fitting 1 comprises a substantially rigid hollow sleeve 2, preferably made of metal, to be inserted in an end of the pipe P, a clamp member 3 having a internally threaded portion to be tightened on the terminal T, and an elastic bushing 4 interposed between the clamp member 3 and the pipe P. Bushing 4 has the function of pressing the end of the pipe P against the hollow sleeve 2 and/or against the terminal T when the clamp member 3 is being tightened on the terminal T.

Electrical insulating means 5 are further provided, which are designed to prevent the passage of stray currents between the pipe P and the terminal T.

A peculiar feature of the invention lies in that the electrical insulator means 5 comprise a gasket 6 made of an electrically insulating base material having an axial tubular

portion 7 adapted to be interposed between the hollow sleeve 2 and the inner surface 8 of the end of the pipe P.

Furthermore, the axial tubular portion 7 is joined to a radial portion 9, which is designed to be interposed between the terminal T and the front edge F of the end of the pipe P.

Thus, the sealing action and the electro-corrosion resistance may be jointly increased as compared with prior art.

Particularly, the shape of the gasket 6, comprising the axial tubular portion 7 and the radial portion 9, effectively prevents any contact between the metal terminal T and the metal layer of the pipe P. This prevents any passage of stray currents as well as any electro-corrosion problem due to the contact between different metals.

The axial tubular portion 7 may have an outer cylindrical sealing surface 10 designed to come in contact with the inner surface 8 of the pipe P, and the radial portion 9 may have a substantially flat sealing surface 11 designed to come in contact with the front edge F of the end of the pipe P.

Furthermore, the substantially flat sealing surface 11 may have a portion designed to come in contact with a peripheral edge 12 of the bushing 4. By this arrangement, both the front edge F of the pipe P and the peripheral edge 12 of the bushing 4 may be pressed against the radial portion 9, thereby allowing to increase the sealing action and to safely lock the gasket 6. In fact, the latter cannot be excessively displaced or deformed while it is being mounted, and will effectively provide the desired electrical insulation.

In order to increase the sealing action at the cylindrical sealing surface 10 and the substantially flat sealing surface 22, the base material of the gasket 6 may be of the polymeric type and be elastically deformable. Especially, the use of an

elastomer, e. g. NBR, proved to be particularly effective. By using a deformable polymeric material, the compression of the gasket 6 may be controlled by adjusting the tightening of the clamp member 3. Particularly, it is possible to alternate between a relatively low compression level, adapted to provide a hydraulic and mechanical seal, as shown in FIGS. 2 and 6, and a relatively high compression level, adapted to increase the previously achieved hydraulic and mechanical seal, as shown in FIGS. 3 and 7.

Advantageously, sleeve 2 may have external ridges 13 which are designed to at least partly penetrate the inner surface 8 of the pipe P during mounting and prevent any accidental release of the sleeve 2 from the pipe P. In order to help the external ridges 13 to penetrate the inner layer of the pipe P, the base material of such layer may be arranged to be more resilient than the external ridges 13. Especially, the ridges 13 may have a helical shape to allow easy and selective mounting and dismantling of said sleeve with respect to the pipe P. In fact, thanks to this particular feature, the sleeve 2 may be inserted or removed by imparting thereon a rotary and translatory motion with respect to the pipe P.

As shown in the annexed drawings, bushing 4 may have a plurality of longitudinal cutouts 14,15 which extend at least partly along the longitudinal extension of the bushing 4. The longitudinal cutouts 14,15 may allow the deformation of the bushing 4 in the radial direction and to easily compress the end of the pipe P when the clamp member 3 is being tightened on the terminal T. Radial deformability of the bushing 4 may be further increased by making the latter from an elastically deformable polymeric base material. The base material of the bushing 4 may also provide electrical

insulation, to further prevent the passage of stray currents and generally improve electrical insulation between the pipe P and the terminal T. In a particular, non limiting embodiment, the bushing 4 is made of a glass fiber-reinforced nylon.

As described above, the peripheral edge 12 of the bushing 4 may be pressed against the flat sealing surface 11 and also the inner surface 16 of the bushing 4 may be radially pressed against the end of the pipe P. To obtain this double compression effect, the bushing 4 may have a frusto-conical outer surface 17, which is adapted to interact with a complementarily shaped inner surface 18 of the clamp member 3.

Furthermore, bushing 4 may have circumferential ridges 19 on its inner surface 16, which are designed to interact with the outer surface of the pipe P to prevent the bushing 4 from axially slipping away from the pipe P while the clamp member 3 is being tightened. Therefore, not only the peripheral edge 12 of the bushing 4, but also the front edge F of the pipe P may be effectively pressed against the flat sealing surface 11 of the gasket 6. More in detail, upon tightening of the clamp member 3, the circumferential ridges 19 may slightly penetrate the outermost layer of the pipe 9 without tearing the layer, thereby allowing to integrate together the pipe P and the bushing 4 as they press against the gasket 6.

In accordance with another preferred arrangement, as shown in FIGS. 20-23, the bushing 4 may have an annular ridge 17'on its outer surface 17, for slidably interacting with a housing 18', itself having an annular shape, and formed on the inner surface 18. Therefore, a radial compression effort may be

imparted on the pipe P, thereby reducing the axial sleeve 2 insertion effort, thereby facilitating such insertion.

Advantageously, housing 18'may have a greater inclination than the inner surface 18. Hence, once the member 3 has been clamped, a radial increase of the mechanical and hydraulic seal of the pipe P on the sleeve 2 will be obtained.

Suitably, the annular ridge 17'may have a substantially circular and flat end surface S, adapted to abut against a corresponding stop surface S'formed in the housing 18', to act as a stop and prevent the bushing from assuming wrong positions.

Advantageously, the inner surface 16 of the bushing 4 may also have longitudinal ridges 20 for interacting with the outer surface of the pipe P to prevent the bushing 4 from rotating when the clamp member 3 is being tightened on the terminal T. More in detail, the circumferential ridges 19 and the longitudinal ridges 20 may be integral with the bushing 4 and may be made, like the latter, from an elastically deformable polymeric material. Suitably, the ridges 19,20 may be less resilient than the outer layer of the pipe P to facilitate their penetration of such layer. The circumferential ridges 19 on an axial sectional plane and the longitudinal ridges 20 on a transverse plane may have a suitably sized rounded profile, to be effective and further prevent the tear of the outermost layer of the pipe P.

Suitably, bushing 4 may have indication means for visually showing a user the level of radial compression of the bushing 4. Particularly, the indication means may be defined by at least one 15 of the longitudinal cutouts of the bushing 4,

which may extend along the whole longitudinal extension thereof to the end portion 21 of the bushing 4 which projects out of the clamp member 3 and is visible from the outside.

Therefore, when the clamp member 3 is at least partly tightened on the terminal T, the end portion 21 of the bushing 4, as well as a portion of the longitudinal cutout 15 may be visible from the outside. Also, if the amount of tightening of the clamp member 3 and the level of radial compression of the bushing 4 are relatively small, the facing edges 22,22'of the longitudinal cutout 15 may be visually spaced apart. However, when the amount of tightening of the clamp member 3 and the level of radial compression of the bushing 4 are relatively high, the facing edges 22,22'of the longitudinal cutout 15 may be visually closer together.

Hence, when the clamp member 3 is at least partly tightened and the facing edges 22, 22'are visually spaced apart, the hydraulic and mechanical seal is provided, whereas when the facing edges 22, 22'are visually closer together, an increased hydraulic and mechanical seal is obtained.

Moreover, the end portion 21 of the bushing 4 may be sized to prevent the clamp member 3 from scratching the pipe P as the member 3 is being tightened, and to further protect the pipe from other damages.

Sleeve 2 may have a housing 23 for the gasket 6, on its outer surface. Also, in a particular embodiment of the fitting 1, as shown in FIGS. 1-4, sleeve 2 is separated from the terminal T and may be selectively inserted therein. In this embodiment, the sleeve 2 has an end portion 24 which is adjacent the housing 23 and designed to be inserted in the terminal T. Furthermore, in the same embodiment, the gasket 6 may have an end edge 25 which is connected to the radial

portion 9 and is designed to contact an inner surface of the terminal T, as shown in FIG. 13.

As shown in Fig. 10, sleeve 2 may have a recessed hexagonal housing 26 at its end portion 24, wherein a tool 27 may be inserted for mounting and removing the sleeve 2 to and from the pipe P.

In a further embodiment of the fitting 1, as shown in FIGS.

5-8, alternative to that described above, sleeve 2 is integrally joined to the terminal T in the proximity of the. housing 23.

The above description clearly shows that the inventive fitting fulfils the above objects and particularly the shape of the gasket allows to achieve a high sealing action, while preventing the passage of stray currents and avoiding any electro-corrosion due to the contact between different metals.

The fitting of this invention is susceptible of a number of changes and variants, within the inventive concept disclosed in the appended claims. All the details thereof may be replaced by other technically equivalent parts, and the materials may vary depending on different needs, without departure from the scope of the invention.

While the fitting has been described with particular reference to the accompanying figures, the numerals referred to in the disclosure and claims are only used for the sake of a better intelligibility of the invention and shall not be intended to limit the claimed scope in any manner.