AUTOMATIC SHUT-OFF DEVICE FOR COMPRESSED OR LIQUEFIED GAS VALVES DESCRIPTION OF THE INVENTION The present invention is concerned with an automatic shut-off device for a valve for compressed or liquefied gases comprising a valve body designed to be mounted on a gas cylinder and provided with an internal passage that allows the cylinder to be filled with pressurized gas. Although not restricted thereto, the invention more specifically aims at a valve of the type described in U.S. Patent 5,282,496. This patent is concerned with a valve for refillable cylinders and comprising a level regulating valve to prevent the cylinder from being possible. filling beyond a certain limit, for example 80% of its maximum capacity, to avoid potential risks of an accident. However, there are still risks of an accident whether the cylinders are filled by non-specialists and they do not have level regulating valves as proposed in the above mentioned patent or if they are filled with an inappropriate gas Q if the user seeks to neutralize the valve regulatory level or even for other reasons. The object of the present invention is to provide a simple and effective automatic quenching device
REF.121218 for a valve as described in the preamble and that prevents a gas cylinder from being filled by a non-specialist or non-authorized individual who does not have special equipment. In order to obtain this objective, the invention provides an automatic shut-off device as described in the preamble, which is characterized in that the internal passage has an enlarged cross-section containing a ball sensitive to a magnetic field and of a larger diameter than the diameter of the passage and acting as a unidirectional valve element when blocking the passage in the direction of filling and because the valve element can be neutralized by moving the ball sideways under the effect of a magnetic field generated by a magnet placed on the outside of the valve. Consequently, any attempt to fill the cylinder is bound to fail since the ball, under the effect of its own weight and the pressure of the filling gas is pressed against its seat which is formed by the upper edge of the passage and closes the passage to the inside of the cylinder. Only someone who knows how to open the passage and is in possession of an appropriate magnet will be able to carry out the filling once the ball is removed from its seat using this magnet. Any attempt to fill the cylinder, when the cylinder rests on one side is also destined to fail. Alternatively, by arranging the cylinder for the passage it can be opened because the ball, under the effect of its own weight, moves away from its seat, but the filling gas pressure returns the ball on its seat and automatically closes the ball. passage. According to a preferred embodiment, there is a tube made of a synthetic material inside the axial passage. The upper edge of this tube serves to form the seat for the ball. It is also possible to devise a niche in the region of the ball in the outer wall of the valve body and which is intended to accommodate a magnet in a complementary manner. Therefore, it is not only necessary to have a magnet available to open the device, but also, this magnet must have a special shape suitable to fit that of the niche. The valve may also comprise means for preventing the ball from clogging the top passage above the enlarged cross section. These means may consist of a polygonal cross section of this passage or of a spring provided between this passage and the ball. Other specific features of the invention will emerge from the description of an advantageous embodiment, presented below by way of illustration, with reference to the accompanying drawings in which:
Figure 1 shows a partial cross-sectional view through the body of a valve provided with a first embodiment of an automatic shut-off device according to the present invention in the off position; Figure 2 is a view similar to that of Figure 1 but during the neutralization phase; Figure 3 illustrates a partial cross-sectional view through the body of a valve provided with a second embodiment of an automatic shut-off device according to the present invention, in the off position; Figure 4 illustrates a view similar to that of Figure 3 but during the neutralization phase; Figure 5 shows a view similar to that of Figure 3, while the gas is extracted from the gas cylinder; Figure 6 is a cross-sectional view in the sectional plane VI-VI of Figure 5 and Figure 7 is a partial cross-sectional view of a third embodiment. Reference 10 denotes part of a valve designed to be mounted on a refillable gas cylinder. The reference to a gas cylinder is not restrictive and extends to cover all kinds of vessels. This may be a valve as described in U.S. Patent 5,282,496 or any other device that allows the cylinder to be filled with or without a level regulating valve, which operates with a directional valve or a unidirectional valve. The body 10 has an axial passage 12 communicating with the interior of the cylinder, not shown. At a certain point, this passage ends in an enlarged portion 14 containing a spherical metallic ball 16, preferably made of special steel. This ball normally rests on its seat which is formed by the upper edge of the passage 12 and therefore prevents the filling gas from entering the cylinder. Figure 2 shows the neutralization of the device using a powerful magnet 10 which is brought closer to the body 10 of the valve in the region of the ball 16 and whose magnetic field is powerful enough to move the ball 16 away from its seat and open the passage to the filling gas. The magnet 10 can be a simple permanent magnet. In order to further complicate the task of someone who wishes to discover how to neutralize the shutdown system and can reach it from a magnet in order to fill the cylinder, it is possible to provide a niche in the wall of the body 10 to which niche the magnet has to be introduced. This niche could extend so far to close the enlarged portion 14 and would also have the additional advantage of bringing the magnet even closer to the 16th ball. Figures 3 and 4 show one such modality with a cut or niche 22 on the wall 10 in the region of the enlarged portion 14. The niche 22 may be cylindrical or frustoconical as shown in the figures. In the vertical section in the figures, the niche 22 can have a round or polygonal cross section, for example a triangular cross section. In order to have the ability to move the ball 16 away from its seat and discover the passage 12, it is therefore necessary to have to use a magnet 12 (figure 4) which has a form that is complemented with that of the niche 22. In order to further complicate the task of people who are not authorized, to fill the gas cylinder, it would be possible, at the bottom of the niche, to provide an axial rod, so that the magnet to be introduced to the niche would have to have corresponding perforation in its head in such a way that it could be introduced to the niche 22. In the case of a niche 22 and a magnet 24 which are cylindrical, it would also be possible to provide these with complementary screw threads, possibly from a Special type of threading, in such a way that the magnet would have to be threaded to the body 10 of the valve. Therefore, it would be impossible for the quenching to be neutralized with a magnet that could be supplied in the open market. In the modality of figures 3 and 4, the enlarged cross section 14 need not extend by 360 ° and may be restricted to a lateral notch in the region of the niche 22. However, for reasons of ease of manufacture, it may be preferable that the flare 14 is also provided, in the case of figures 3 and 4, across the entire circumference. Figures 3 and 4 also show, in the manner of a variation, a tube 26 provided in the passage 12 and on the edge -of which it is proposed to form the seat for the ball 16. This tube can be made of a synthetic material, for example nylon and its purpose is to ensure a better quenching in the 16 ball compared to metal-to-metal contact. If, as is generally the case, passage 12 is used for the gas passage when the cylinder is filled with gas and gas is extracted therefrom, a problem may arise when the gas is removed. Specifically, as shown in Figure 5, when the gas is removed, the pressure of the gas is sufficient to lift the ball 16 and hold it against the lower edge of the upper passage 28, which leads to the seat 30 of the non-illustrated shut-off element of the valve , which would close the passage 28 and prevent the gas from being extracted. To solve this problem it is possible, in the lower part of the passage 28, to provide an obstacle in the form of a metal rod which prevents the ball 16 from obstructing the passage 28. It is also possible to convert the circular cross section of the passage 28, so minus the lower region 28, to a polygonal cross section, for example a square cross section as shown in Figures 3 to 5 and more in particular in the cross-sectional view of Figure 6. Thus, when the ball 16 is forced against the lower end of the passage 28 still remains, in several instances, in particular this particular instance four passage 30 for the gas at the four corners. Figure 7 shows other means designed to prevent the passage 28 from being obstructed by the ball 16 when the gas is removed. In this embodiment, there is a spring 34 provided between the ball 16 and the passage 28 which is by reference, extended downward by a circular axial flange 32 to ensure that the spring is retained. The force of this spring 34 is large enough to keep the ball 16 in a floating state away from the rim 32 during a normal gas extraction operation. In an advantageous embodiment, it is possible to benefit from the presence of this spring 34 to design it as a flow restrictor or safety valve. Such limiters are known per se and are used to shut off the gas flow when the flow rate or pressure exceeds a predetermined limit. This can arise in particular in the case of an accident, for example if the valve breaks. All that is required then is simply to force the spring 34 sufficiently so that it prevents the passage 28 from being closed by the ball 16 under normal gas pressure and normal flow velocity conditions but allows the quenching in the case of a abnormal operation. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that it is clear from the present description of the invention.