The present invention concerns a system for the leaktight connection of valve units to respective pipes, according to the characteristics mentioned in the preamble of the main claim. Technological background

The invention lies particularly, but not exclusively, in the specific field of systems for the leaktight connection of valve units arranged for delivering combustible gas to burners of heating apparatuses, such as boilers, fireplaces or the like.

In this field, in order to connect the valve unit to the gas pipes, it is known to arrange in the body of the unit itself respective threaded male attachment elements, which can be connected to the respective pipes by pipe-fixing ring-nut means, screwed onto the attachment in a manner such as to retain an end of the pipe in a gas-tight manner on the body of the valve unit. A typical solution provides for the attachment element to be provided at its free end with a front surface which can be coupled to one end, preferably with countersunk profile, of the corresponding pipe, in order to ensure a gas-tight seal in the coupling of such surfaces as a result of the clamping, by screwing, of the ring-nut on the threaded spigot of the attachment element. An example of such a connection system is described in Italian Patent Application No. PD2006A000080 in the name of the Applicant. Systems for leaktight connection, in particular between tubular sections of pipes, are also known in which the axial retention between the sections is obtained by the action of resilient retaining elements, such as wire clips or similar devices, which can be releasably connected between the tubular sections and which act between same in order to ensure mutual gas-tight axial clamping between the coupling tubular sections. Such systems prove effective owing to the ease and rapidity of use, as well as the fact that they result in structural simplifications, in terms of overall dimensions and number of parts required for the connection. Description of the invention A principal aim of the invention is that of providing a system for the leaktight connection of valve units to respective pipes which permits gas- tight connection, on the same valve body, to different types of pipes, and in particular which permits, as an alternative, leaktight connection both to clamping means with threaded ring-nut and to connecting means having releasable resilient retaining elements, thus widening the range of possible connections provided in the installation stages with the same valve unit.

These and other aims which will become clearer hereinafter are achieved by means of a system for leaktight connection produced according to the following claims. Brief description of the drawings

Further characteristics and advantages of the invention will become clearer from the following detailed description of a preferred exemplary embodiment thereof, illustrated by way of non-limiting example with reference to the appended drawings, in which: - Figure 1 is a perspective view of a valve unit connected to a pipe in a leaktight manner according to the connection system of the invention,

Figure 2 is a perspective, exploded, view of the connection system of the preceding Figure, - Figure 3 is a front view of the valve unit of Figure 1, in which the connection system is in the coupled state,

Figure 4 is a view in section along the line IV-IV of Figure 3,

Figure 5 is a view in section along the line V-V of Figure 3,

Figure 6 is a schematic sectional view of a valve unit operating with the connection system of the invention, used in a leaktight connection of known type to a pipe,

Figure 7 is a view corresponding to that of Figure 5 in an alternative embodiment of the invention. Preferred exemplary embodiments of the invention With reference to the drawings mentioned, the reference 1 designates as a whole a valve unit, shown only partially, arranged to be connected to a pipe 2, according to a system for leaktight connection provided according to the present invention. The pipe may form the supply pipe or delivery pipe for the gas relative to the valve unit. Provision may also be made for both the supply pipe and the delivery pipe for the gas to be arranged to be connected in a leaktight manner to the body Ia of the valve unit by means of the system of the invention. A description will therefore now be given of the connection system with reference only to the pipe 2, within the limits of the aforesaid explanation. Said tube is connected to the valve unit in the region of an attachment provided on the body Ia of the valve unit. Said attachment is of the threaded engagement type and comprises a male attachment element 3, formed integrally with the valve body Ia and projecting axially therefrom, as shown in the drawings. More particularly, the threaded attachment element 3 is cylindrical in shape and has an axial cavity 4, in the form of a cylindrical through bore, intended to place the pipe 2 in flow communication with the gas through-flow inside the valve unit. The through cavity 4 is coaxial with the cylindrical threaded attachment 3, with X indicating the direction of their axial extension. The attachment element, starting from the valve body Ia, comprises a first portion including a groove 5, extending for at least part of its circumferential profile, and a second cylindrical portion, in prolongation of the first portion, and on which the external thread of the attachment is provided. At the free end of the attachment an annular front surface 6 is defined.

In the groove 5, in a position adjacent to the threaded portion of the attachment, a shoulder surface 5a is defined, the function of which will become clear from the continuation of the description.

A further radial shoulder surface, indicated by 7, is provided inside the axial cavity 4 and is defined, in the direction of the free end of the attachment, between a first axial part of the cylindrical cavity 4 and a second axial part of the cavity, adjacent to the first part and having a larger diameter than said first part, as is clearly shown in Figures 4 and 5.

Correspondingly, the pipe 2 comprises in its outer cylindrical surface, in the region of the end connectible to the valve unit, a shoulder surface 8. The radial shoulder is defined between a first axial pipe portion 2a, extending from the free end of the pipe itself, and a second axial portion 2b of the pipe, adjacent to the first portion and having a smaller diameter than the first portion. In the first pipe portion 2a a circumferential seat 9 is also provided, intended to house a sealing ring 10, for example of the O-ring type, in order to ensure gas-tightness in contact with the inner surface of the axial cavity 4, following the connection by engagement of the pipe 2 in the cavity itself.

The connection system also comprises a retaining element, indicated as a whole by 11, which can be restrained axially, and releasably, on the valve body Ia, and can also itself retain the pipe 2, in a manner secured to the valve unit and gas-tight, as will become clear from the following description.

More particularly, the retaining element 11 is formed as a clip made of . metal sheet, for example of harmonic steel, which has a preferred forked shape with two opposed arms 12, 13 connected to each other at one end by a linking portion 14.

In the arm 12, a pair of opposed branches 12a, 12b are defined, extending substantially parallel to each other and also spaced apart. They are also connected at their free ends, on the side remote from the linking portion 14, by a connecting crosspiece 15.

Similarly, in the arm 13 a pair of branches 13a, 13b are defined, extending substantially parallel and spaced apart from each other. The reference 16 indicates a corresponding connecting crosspiece for the branches 13a, 13b. It should be noted that the arms 12, 13 are shaped as mirror-images of each other with respect to a central median plane of symmetry, passing perpendicularly to the upper flat linking portion 14 of the clip.

In each of the branches 12a, 13a, which are diametrally opposed with respect to the direction X in the stage of connection of the clip to the valve body, a respective central portion 12c, 13c with curved profile is defined, the radius of curvature of which is selected such that the portions are in abutment against the shoulder 5 of the groove 5, as a result of the connection of the clip to the valve body. Similarly, in each of the branches 12b, 13b, which are also diametrally opposed, a respective central portion 12d, 13d with curved profile is defined, the radius of curvature of which is selected such that the portions are in abutment against the shoulder 8 of the pipe 2, as a result of the connection of the clip to the valve body.

Further indicated by 15a, 16a are the respective through openings which are defined in the arms 12, 13, by the continuous peripheral profile delimited by the opposed branches and by the connecting portions of same.

Provision is also made for the ends of the arms 12 and 13, on the side remote from the upper linking portion 14, to be bent back to diverge from each other, as illustrated in Figure 2, so as to facilitate the step of connection and disconnection of the clip to and from the valve body.

The connection system of the invention provides that, starting from the position of Figure 2, with the parts disengaged, with mutual axial spacing, the pipe 2 is inserted with its portion 2a into the cylindrical axial cavity 4 of the valve body. The insertion is completed when the free end of the pipe is in abutment againstthe internal shoulder 7. In this position the sealing ring 10 is in contact with the cylindrical surface of the cylindrical cavity 4, ensuring, , by means of appropriate choice of dimensions, the gas-tight seal between the coupled cylindrical surfaces. When the axial engagement position is completed, the clip element

11, in a movement transverse to the axis X, is fitted onto the attachment 3, with prior resilient opening out of the arms 12 and 13 (as a result of the interference encountered through the presence of the cylindrical threaded portion of the attachment itself). The movement transverse to the axis X is completed when the portions 12c, 13c of the clip are engaged in the groove 5, engaging in abutment against the shoulder 5a. At the same time, the portions 12d, 13d are caused to engage the outer surface of the pipe by abutting against the shoulder 8. The action of opposed abutment between the shoulders 5a and 8, owing to the axial rigidity of the clip (with an- appropriate predefined axial distance between the branches of the arms which act on the same side), ensures the axial retention of the pipe relative to the valve body Ia, completing the leaktight connection between same.

In order to disconnect the pipe 2 from the valve unit, it is sufficient to disconnect the resilient clip, by means of a reverse transverse movement, until the arms are disengaged from the respective coupled surfaces. The resilience of the arms themselves permits the resilient opening out necessary for the withdrawal of the clip away from the operative connection position described above. It should be noted that the presence of the openings 15a, 16a in the respective arms of the clip 11 allows it to be fitted onto the threaded portion of the attachment, without interfering with the attachment itself. As a result, the system lends itself advantageously to being employed in valve units provided with threaded male attachments, of the type described, the threads of which are intended to be engaged by pipe-fixing ring-nuts, whenever a conventional type of leaktight connection is opted for, which can be provided as an alternative to the connection system of the invention, the two systems being thus able to co-exist and be employed as an alternative to each other for the same valve unit, and in dependence on the different type of pipe selected for connection to the valve unit, all of which widens the possibilities of connection provided in the stage of constructional installation of the valve unit with the corresponding pipes.

Figure 6 illustrates schematically a conventional type of connection in which the valve unit 1 described above is connected in a leaktight manner to a pipe 2' which has a frontal annular end edge 20 which can, be surface connected, by superposition, to the front surface 6 of the attachment. For leaktight clamping of the surfaces in contact, a respective pipe-fixing ring-nut or nut 25 is provided, fitted onto the corresponding pipe and including an internally threaded cylindrical seat 25a, the nut- screw of which can be engaged by screwing on the corresponding threaded portion of the attachment 4. The screwing action effects the axial clamping between the surfaces 6 and 20 in mutual contact.

An optional sealing ring 31 may be interposed between the aforesaid surfaces in order to ensure gas-tightness between the coupled parts. Figure 7 (for axial symmetry only half a section is shown) illustrates an alternative embodiment of the invention, in which details analogous to those of the example of Figure 5 are designated by the same reference numerals. This variant differs principally in that the sealing ring 10, of the O-ring type, is pre-mounted in the axial cavity 4 of the valve body Ia, for example housed in a suitable seat formed in the cylindrical wall of the cavity. This permits simpler execution of the portion 2a of pipe 2, as is clearly shown in Figure 6. Said pipe conveniently has a pinch 2c protruding circumferentially and which defines a circumferential raised portion which can abut between the front surface 6 of the attachment and the. portions 12d, 13d of the clip, thus effecting the axial clamping of the pipe 2.

It is also to be understood that the retaining element may assume a different shape from that previously described, but in any case such as to have at least a first and a second surface portion, spaced apart from each other axially and which can also abut against the shoulders 5a and 8 so as to secure and axially restrain the parts coupled to each other. It is also understood that the clip may be of a different material and shape, but still within the same inventive concept which is the basis of the system claimed.

The invention thus achieves the aims proposed, obtaining the advantages mentioned above compared with the known solutions.