SAFETY DEVICE FOR DETECTING A FLOW OF FUMES INSIDE AN EXHAUST PIPE

Abstract: A safety device for detecting a flow of fumes inside an exhaust pipe of a gas apparatus for producing sanitary hot water and/or for room heating, comprising a main body (2,5) which, in use, is fixed inside a fumes exhaust pipe. On the main body a mobile element (10) can oscillate, with respect to the main body, about an axis (9) basically perpendicular to the outflow of the fumes passing through the exhaust pipe. A position transducer (8, 13) detects at least two positions of the mobile element in relation to the main body, corresponding with a flow of fumes respectively higher or lower than a threshold value, and generates a signal which indicates said two positions. The transducer is preferably comprised of a Hall-effect sensor (8) mounted on the main body (5) and of a magnetic element (13) mounted on the mobile element (10).

Description: Description Safety device for detecting a flow of fumes inside an exhaust pipe Technical Field The present invention relates to a safety device for detecting a flow of fumes inside an exhaust pipe of a gas apparatus for producing sanitary hot water and/or for room heating. Background Art In gas apparatus for producing sanitary hot water and/or for room heating, especially for domestic use, it is of primary importance to envisage safety systems that interrupt the gas inflow if the water heater fails to function normally. Safety devices which detect the flow of fiunes in the exhaust pipe and interrupt the gas inflow whenever said flow is lower than a predetermined value are known. According to some systems of a known type, a wide opening has to be made on the fumes exhaust pipe which allows for the passage of levers or other mechanisms operating a traditional switch which, owing to the high temperatures reached by the exhaust fumes in the pipe, must be placed out of said pipe. Other systems of a known type are based on the use of differential pressure switches and are, therefore, very complex and expensive, both because of the cost of the component itself and of the costs related to the sample taking of the necessary pressure signals. Disclosure of Invention The aim of the present invention is to overcome the drawbacks of the prior art technique, providing, in particular, a safety device small enough to be fitted easily and completely inside an exhaust pipe and which can ensure its safe and reliable operation for a long time despite the aggressive action of the water heater exhaust fumes. In order to achieve the aim mentioned above, the subject of the present invention is a safety device of the kind mentioned in the preamble of the current description, characterised in that it comprises a support body which, when in use, is fully contained within a fumes exhaust pipe, the following elements being installed on said support body: a mobile element which, when in use, can oscillate about an axis because of the thrust exerted thereon by the fumes passing through the exhaust pipe, and a position transducer detecting at least two positions of the mobile element in relation to the support body, with said at least two positions corresponding, in use, to a flow of fumes respectively higher and lower than a predetermined threshold value. In a preferred embodiment, when the device is reached by the water heater exhaust fiimes, the mobile element closes on the support body so as to form therewith a casing for the transducer, thus preserving it from the aggressive action of the exhaust fumes. According to a further embodiment of the present invention, a Hall- effect transducer is mounted on the support body, which is preferably but not exclusively temperature compensated and which can detect the possible proximity of a magnetic plate mounted on the mobile element. Another characteristic of the present invention consists in the arrangement of an elastic element, preferably a helical flexure spring or a so-called needle spring (also named torsion spring) which makes the mobile element rotate in order to move it away from the support body if the exhaust flow of fumes is insufficient or absent. Further characteristics and advantages of the present invention will better emerge from the detailed description of a preferred embodiment that follows, in the form of a non-limiting example, with particular reference to the figures of the accompanying drawings, in which: figure 1 is a perspective view of a safety device according to the present invention in an alarm open configuration, figure 2 is a cross section of the safety device according to line II-II of figure 1, and figure 3 is a cross section similar to that in figure 2, wherein the safety device is in a regular operating closed configuration. With reference to the drawings, a safety device for detecting a flow of fumes inside an exhaust pipe of a gas water heater, globally indicated by reference number 1, comprises a hollow drum 2 fitted in one of its lower parts 2a with an annular flange 3 for mounting the device into the exhaust pipe. On the side opposite to flange 3, the drum 2 is closed by a bottom wall 4 from which a fixed valve 5 protrudes with a leading edge 15 and a trailing edge 16. On the concave internal wall 5a of the fixed valve 5 is a hollow case 6 communicating with the internal cavity of the drum 2 and accessible by the rear side 2a of the drum 2. In the hollow case 6 a platelet 7 is to be found to which a Hall-effect transducer 8 of a generally known type is fixed that is preferably but not exclusively temperature compensated. The compensation circuit and the circuit processing the possible signal of the transducer 8 is fitted correctly inside the drum 2 in such a way that only electrical signal conductors (not illustrated in the figures) come out of said drum 2. A shaft 9 is aligned with and along the leading edge 15 of the fixed valve 5, and a mobile valve 10 is hinged onto said shaft which is basically complementary with the fixed valve 5 and which, in its closed position illustrated in figure 3, forms with said fixed valve 5 an aerodynamic structure which is basically symmetric with respect to the layout plane Y-Y of figures 2 and 3. A helical flexure spring 11 is positioned on the shaft 9 and pushes the mobile valve 10 towards the opening position illustrated in figures 1 and 2. A seat 12 for a magnetic capsule 13 is constructed on the mobile valve 10, in a longitudinal position corresponding with the position of the transducer 8, said magnetic capsule 13 being fixed by joining, by gluing or by any other known means. A cap 14 coupled onto the end of the shaft 11 prevents the mobile valve 10 from being extracted and closes, on the front side, the aerodynamic structure formed by the two valves 5,10 in the closing position of figure 3. By means of the flange 3, the safety device 1 is mounted onto the inside wall of a fumes exhaust pipe of a gas water heater. On said internal wall of the pipe, within the covered area of the drum 2, a small hole has been made to enable the passage of the electrical signal conductors connected to the transducer 8. For increased safety, it is possible to position a gasket between the pipe wall c and the flange 3, so as to prevent the exhaust fumes from passing through the drum 2 and from coming out of the exhaust pipe through the small passage hole for the electrical conductors. The safety device 1 is mounted with the symmetry plane Y-Y basically parallel to the exhaust flow of fumes and oriented in such a way that the leading edge 15 is reached by the fumes first. When used in normal operating conditions, if the exhaust flow of fumes is higher than a predetermined value deemed sufficient in the design phase, the fumes press onto the external wall of the mobile valve 10 against the spring 11 so as to bring the device to the closed configuration illustrated in figure 3. In this position, the Hall effect transducer 8 is reached by the magnetic field generated by the capsule 13, thus generating an electrical field of a predetermined value which represents a normal operating condition. If, for any reason, the flow of fumes falls below a threshold value or becomes null, the spring 11 opens the mobile valve 10 pushing it towards the position illustrated in figure 2, thus pushing the capsule 13 away from the transducer 8 which generates, therefore, a signal of a different value which represents an alarm condition. The signals generated by the transducer 8 are processed by a circuit of a generally known type positioned inside the drum 2 and/or outside the exhaust pipe which - when an alarm signal is given - activates alarm and safety means, for example interrupting the gas outflow and/or activating acoustic, visual and similar signals. As an alternative to the Hall-effect transducer 8 mentioned above in the description of a preferred embodiment of the present invention, the device 1 can be fitted with position transducers of a different type, for example resistive, capacitive, inductive or electromagnetic types. In an alternative example of a preferred embodiment, the mobile valve 10 can be fixed to the rotating cursor of a potentiometer connected to the fixed valve 5 or to the drum 2. An important advantage of the present invention is the small number of components that form the safety device. In systems where the Y-Y plane is positioned vertically with the leading edge 15 oriented downwards, it is also possible to avoid the elastic action of the spring 11, as the weight of the mobile valve and of the capsule 13 is enough to make the device open if the exhaust flow of fumes is insufficient. A very important advantage of the preferred embodiment of the present invention, illustrated in the drawings, is that the sensitive part of the Hall-effect transducer 8 and all the electrical connections, as well as the possible control circuit housed in the drum 2, are never in direct contact with the exhaust fumes which, otherwise, could also attack said components from a chemical point of view. Obviously, by maintaining the principle of the present invention, various embodiments are possible and the relevant details can be varied widely with respect to this description and its illustration without falling outside the scope of the present invention.

Claims: Claims. 1. A safety device for detecting a flow of fumes in an exhaust pipe of a gas water heater, characterised in that it comprises a main body (2,5) which, in use, is fixed inside a fumes exhaust pipe, the following elements being mounted on said main body: a mobile element (10), which can oscillate with respect to the main body around an axis (9) basically peφendicular to the outflow of the fumes passing through the exhaust pipe, and a position transducer (8,13) detecting at least two positions of the mobile element in relation to the main body, said at least two positions corresponding with a flow of fumes respectively higher and lower than a predetermined threshold value, said transducer thus generating a signal representative of said two positions. 2. A safety device according to claim 1, wherein the position transducer comprises a Hall-effect sensor (8). 3. A safety device according to claim 2, wherein the Hall-effect sensor (8) is mounted on the main body (5) in order to detect the proximity of a magnetic element (13) mounted on the mobile element (10). 4. A safety device according to claim 3, wherein the Hall-effect sensor (8) is positioned in the case (6) on the main body (5). 5. A device according to any of the previous claims, wherein the main body comprises a hollow drum (2) from which a fixed valve structure (5) protrudes with a leading edge (15) and a trailing edge (16), said mobile element including a mobile valve structure (10) articulated at the trailing edge (16) of the fixed valve (15) and forming therewith, in a closed configuration, an aerodynamic structure. 6. A safety device according to any of the previous claims, characterised in that it comprises elastic means to force at least a part of the mobile element (10) into a position distant from the main body (5) against the thrust exerted on the mobile element by the flow of fumes passing through the exhaust pipe.

Inventors: MARCHETTI RUGGERO, MARCHETTI, RUGGERO
Applicants: MARCHETTI RUGGERO, MERLONI TERMOSANITARI SPA, MARCHETTI, RUGGERO, MERLONI TERMOSANITARI S.P.A.
Application year: 1998
Main classification: F24H9
IPC codes: F24H9, G01F1