AU2005243451B2 - Device for diverting a gas flow through a single-blade flag valve - Google Patents

Description

DEVICE FOR DIVERTING A GAS FLOW THROUGH A SINGLE-BLADE FLAG VALVE Field of the Invention The invention generally relates to a diversion device for the diversion of a gas flow between a primary air flow circuit and a secondary air flow circuit. For example, the gas flow is hot and/or filled with dust and/or containing at least a dangerous even toxic component. Background Art The following discussion of the background to the invention is intended to facilitate an understanding of the present invention only. It should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was published, known or part of the common general knowledge of the person skilled in the art in any jurisdiction as at the priority date of the invention. There exist many different types of devices for diverting gas flows which provides diversion or orientation functions. But, by design, these existing devices usually have the disadvantage of inadequate sealing at the diversion valve element or elements. In the case of separate valve elements, comprising at least one valve element mounted in a primary duct and at least another valve element mounted in a secondary duct, the mixture of gas resulting from a leakage flow from one of these two ducts to the other is certainly limited, but however this limitation is still inadequate to avoid disrupting the smooth operation of a plant fitted with such devices for diverting gas flows between two air flow circuits requiring a good isolation (seal) of one relative to the other.

- 2 Furthermore, when the automated closure/opening valve elements are duplicated, the diversion devices have the disadvantage of being too costly to produce and maintain. There also exist diversion devices with a single damper common to the primary and secondary ducts, which are less costly, but have the disadvantage of less of a seal. Summary of the Invention The device according to an embodiment of the invention is used to orient a gas flow which, in a first configuration, called the normal configuration, is directed towards the primary air flow circuit, and which, in a second configuration is diverted towards the secondary air flow circuit, independent and isolated from the primary circuit, that is to say essentially sealed from this primary circuit. The diversion device according to an embodiment of the invention seeks to find a particularly advantageous application in the air flow circuits that require a good isolation (seal) of primary and secondary circuits one relative to the other, and this even in the presence of different pressures in these two circuits. Furthermore, and as already mentioned hereinabove, the gases of the oriented flow may, where appropriate, contain dangerous, even toxic, constituents, be also filled with dust, possibly harmful, and be hot, for example at a temperature greater than 200'C. In normal operation, such a diversion device directs the gas flow towards the primary circuit, which is open, whereas access into the secondary circuit is closed, the flag damper occupying, in this case, a position called open. On the other hand, in the second -3 configuration, which corresponds for example to the implementation of a particular process, access to the primary circuit is closed whereas the gas flow is directed towards the secondary circuit which is open, the flag damper then occupying a position called closed. The present invention seeks to provide a diversion device with a single valve element (or flag damper) which is better suited to the various requirements of the practice, or to provide the consumer with a useful or commercial choice. For example, there is an improvement of the seal, while reducing the gas mixtures between the two primary and secondary air flow circuits in the common damper. In accordance with an aspect of the present invention, there is provided a diversion device for diverting a gas flow between a primary air flow circuit and a secondary air flow circuit, the diversion device comprising: a section of a primary duct having an entrance and an exit to be connected to the primary air flow circuit, a section of a secondary duct having an entrance which opens into a wall of the section of the primary duct and an exit to be connected to the secondary air flow circuit, a valve element mounted pivotably along one of its edges in the section of the primary duct about a pivot axis transverse to the wall between a first position and a second position, wherein the first position is a position of opening towards the primary air flow circuit in which the valve element closes the entrance of the section of the secondary duct, and the second position is a position of closure of the primary air flow circuit in which the valve element is pivoted away from the entrance of the section of the secondary duct so as to prevent the gas flow from discharging through -4 the exit of the section of the primary duct and divert the gas flow entering via the entrance of the section of the primary duct towards the section of the secondary duct, and a link arm assembly connected to the valve element in order to operate the valve element to pivot between the first and second positions, wherein the valve element has, on a face facing the section of the secondary duct when in the first position, a machined bearing surface to press in sealed manner against a machined seat of an edge of the section of the secondary duct delimiting the entrance of the section of secondary duct, the valve element being mounted pivotably with a limited radial clearance relative to the pivot axis, and wherein when the valve element is in the second position, an opposing edge of the valve element opposing the pivoting edge is resting against an opposing wall of the section of the primary duct opposing the wall of the section of the primary duct into which the section of the secondary duct opens, and two opposing edges of the valve element which are perpendicular to the pivoting edge have a limited clearance with respective opposing walls of the section of primary duct so as not to block the pivoting actions of the valve element between the first and second positions. Preferably, the gas flow is hot and/or filled with dust and/or including at least a dangerous even toxic component. Preferably, the section of the primary duct and/or the section of the secondary duct are rectilinear and tubular of quadrangular cross-section. Preferably, the wall of the section of the primary duct is one of four walls of the section of the primary duct.

Preferably, the valve element is of quadrangular shape and is mounted pivotably substantially along the length of the pivoting edge. Preferably, the machined bearing surface is a machined quadrangular annular bearing surface. Preferably, the pivoting edge of the valve element is bent preferably substantially at right angle to the rest of the valve element and secured, at its lateral ends, to two coaxial cylindrical trunnions of circular cross-section, each pivoting with some radial clearance to respective one of two coaxial bearings secured to at least one of the sections of the primary and secondary ducts. Preferably, at least one of the two bearings is formed by a lateral side plate secured to at least one of the two sections of the primary and secondary ducts, the side plate has a round or oblong opening in which is engaged, with radial clearance, respective one of the two trunnions. Preferably, at least one of the two bearings is formed by a lateral, U-shaped side plate, open in the downstream direction of the section of the primary duct, and the at least one of the two bearings is formed in a housing directly adjacent and downstream to a downstream edge of the entrance of the section of the secondary duct and adjacent an opening in the wall of the section of the primary duct in which the entrance of the section of the secondary duct is made, wherein said downstream is relative to the direction of discharge of the gas flows in the primary duct from its entrance to its exit. Preferably, the diversion device further comprises an elastically deformable metal sealing flap, preferably made of flat spring steel, of substantially - 6 quadrangular form, connected along one of its marginal portions to the wall of the section of the primary duct into which the entrance of the section of the secondary duct opens, at a portion downstream of the entrance relative to the direction of discharge of the gas flows in the primary duct from its entrance to its exit, or to the valve element, and the opposite marginal portion is elastically pressing slidingly against the valve element, or against the wall of the section of the primary duct into which the section of secondary duct opens, at a portion downstream of the pivoting articulation of the valve element, wherein said downstream is relative to the direction of discharge of the gas flows in the primary duct from its entrance to its exit. Preferably, if a is the angle between the axes of the two sections of the primary and secondary ducts oriented from upstream to downstream, the valve element in the second position is pivoted, from the first position, through a maximum angle P limited to 850 or to the angle a, depending on whether the angle a is greater than 850 and less than 1200 or lying between 30* and 85*, and, in the latter case, the minimum angle P is equal to 0.35 a, and wherein said downstream and upstream are relative to the direction of discharge of the gas flows in the primary duct from its entrance to its exit. Preferably, for a given angle a, between the axes of the two sections of the primary and secondary ducts oriented from upstream to downstream, and chosen in an angular range extending from 300 to 1200, and preferably from 30* to 90', the angle P of pivot of the valve element from the first to the second position is chosen such that the pressure losses in the diverted gas flow, when the valve element is in the second position, are minimal, and wherein said downstream and upstream are relative to the direction of discharge of - 7 the gas flows in the primary duct from its entrance to its exit. Preferably, the link arm assembly comprises a link arm and a handle, the link arm assembly is mounted substantially in the central portion of the section of the secondary duct and exerts its action substantially on the centre of gravity of the valve element. Preferably, the link arm assembly is driven by rotating a transverse shaft, traversing the section of the secondary duct and parallel to the pivot axis of the valve element. Preferably, the link arm assembly is actuated by an overlength travel actuator, preferably a rotary cylinder, which, when the valve element is in the first position, holds the valve element such that the machined bearing surface is pressed with force against the machined seat of the section of the secondary duct. Preferably, the actuator is a rotary cylinder which rotates the drive shaft of the link arm assembly and is mounted laterally outside the section of the secondary duct. Preferably, the valve element is stiffened by at least two ribs parallel with one another, and between which a link arm (of the link arm assembly for operating the valve element is articulated. In accordance with another aspect of the present invention, there is provided a diversion device with single valve element flag damper of the type presented above and comprising: a section of primary duct, rectilinear and tubular of quadrangular cross-section, whose entrance and exit are intended to be connected to the primary air flow circuit,a section of secondary duct, also rectilinear, tubular and of quadrangular - 8 cross-section, whose entrance opens into one of the four walls of the section of primary duct, and whose exit is intended to be connected to the secondary air flow circuit, a valve element, of quadrangular shape, mounted pivotingly, substantially along the length of one of its edges, in the section of primary duct, about a geometric axis transverse to the said wall into which the section of secondary duct opens and downstream of the latter, between two positions, a first of which is a position of opening towards the primary air flow circuit in which the valve element closes the entrance of the section of secondary duct, and the second of which is a position of closure of the primary air flow circuit, in which the valve element is moved away from the entrance of the section of secondary duct and pivoted so as to prevent the gas flow from discharging through the exit of the section of primary duct and that the gas flow entering via the entrance of the section of primary duct is diverted towards the section of secondary duct, and a link arm assembly, connected to the valve element in order to operate it by pivoting from one to the other of the said two positions, and which is characterized in that the valve element has, on its face turned towards the section of secondary duct in its first position, a machined quadrangular annular bearing surface to press in sealed manner against a seat formed by machining of the upstream end of the section of secondary duct, delimiting the entrance of the latter in the section of primary duct, the valve element being mounted pivotingly with a limited radial clearance relative to the geometric pivot axis, and in that, in the second position of the valve element, its free edge opposite its pivoting edge is resting against the wall of the section of primary duct which is opposite the wall into which the section of secondary duct opens, the two edges of the valve element which are perpendicular to its pivoting edge having, with the facing walls of the section of primary duct, a limited clearance so as not to block the -9 pivoting actions of the valve element between its two positions. In such a device, the sections of primary and secondary ducts are therefore of rectangular or square section in the zone of action of the valve element, which is most frequently rectangular, and this cross-section of the sections of duct is such that the particles and dust conveyed cannot settle or accumulate in the zone of action of the single, pivoting valve element, which closes the secondary circuit in "open" position and the primary circuit in "closed" position. The limited radial clearance of the pivoting valve element relative to the geometric axis of rotation ensures, in the "open" position, an excellent placement of the valve element, via its machined quadrangular annular bearing surface, against the machined seat on the upstream end of the section of secondary duct, so as to obtain a good sealed pressure of the valve element in the "open" position, that is to say in normal operation, in which the damper is open towards the primary circuit, making it possible to obtain a minimum of 99% of the flow which is directed towards the primary circuit and a maximum of 1% of the flow which may be diverted towards the secondary circuit, which is at a different pressure, and because of small leaks around the closed valve element. In "closed" position, that is to say when the damper is closed towards the primary circuit and open towards the secondary circuit, the device of the invention makes it possible to obtain that, at the minimum, 98% of the flow entering into the secondary circuit originates from upstream of the diversion device, and, at the maximum, 2% of this flow may return from downstream of the primary circuit (downstream of the valve element) into the secondary circuit, because of leaks around the valve element in this position. In an embodiment, to obtain the aforementioned limited radial clearance, the valve element is mounted - 10 pivotingly by an edge folded preferably substantially at right angles to the rest of the valve element and secured, at its lateral ends, to two coaxial cylindrical trunnions with circular cross-section, each pivoting with some radial clearance in one respectively of two coaxial bearings secured to one at least of the said sections of primary and secondary duct. In this case, and in an embodiment of the bearings, at least one of the two bearings, and preferably each of them, is formed by a lateral side plate secured to at least one of the said two sections of duct and having a round or oblong opening in which is engaged, with radial clearance, respectively one of the two trunnions. According to another embodiment, while further improving the seal, at least one of the two bearings, and preferably each of them, is formed by a lateral, U shaped side plate, open in the downstream direction of the section of primary duct, in a housing directly adjacent to the downstream edge of the entrance of the section of secondary duct, downstream of this downstream edge, and open in the wall of the section of primary duct in which the entrance of the section of secondary duct is made. Also for the purpose of further improving the seal in the zone of the edge of the valve element by which the latter is pivotingly mounted, the device also advantageously comprises an elastically deformable metallic sealing flap, preferably made of flat spring steel, of substantially quadrangular form, connected along one of its marginal portions to the wall of the section of primary duct into which the entrance of the section of secondary duct opens, downstream of this entrance, or to the pivoting valve element, and the opposite marginal portion of which is elastically pressing slidingly against the valve element, or - 11 against the said wall of the section of primary duct into which the section of secondary duct opens, downstream of the pivoting articulation of the valve element. According to the design and installation constraints, if a is called the angle between the axes of the two primary and secondary sections of duct oriented from upstream to downstream, this angle a may preferably vary between 300 and 1200 and more preferably between 30 and 900, in order not to increase by too much the loss of pressure created by the gas flow diversion "elbow". According to an embodiment of the invention, the valve element in its second position is advantageously pivoted from its first position through a maximum angle S limited to 850 or to the angle a, depending on whether the angle a is greater than 850 and less than 1200 or lying between 300 and 850, and, in the latter case, the minimum angle B is advantageously equal to 0.35 a. According to installation requirements, for a given angle af, chosen in an angular range extending preferably from 300 to 1200, and more preferably from 300 to 900, the angle P is advantageously chosen such that the pressure losses in the diverted gas flow, when the valve is in the second position, are minimal. In order that the pressure losses resulting from the presence of the link arm assembly in the device are limited, and, furthermore, that this link arm assembly is subjected for as short a period as possible to the effects of the gas, possible corrosive, flow, the link arm assembly advantageously comprising a link arm handle mechanism, is preferably mounted substantially in the central portion of the section of secondary duct and exerts its action substantially on the centre of gravity of the valve element. Thus, this link arm assembly is subjected to the gases only while the flow - 12 is diverted towards the secondary circuit, and, during the operation towards the primary circuit, this link arm assembly experiences only the very limited action of the leakage flow towards the secondary circuit. Furthermore, a point of action of the link arm assembly substantially in the centre of gravity of the valve element makes it possible to require less force to operate the valve element and keep it in tension on its seat, in "open" position. To facilitate the operation, which may be manual, of the link arm-handle mechanism of the link arm assembly, the latter is advantageously driven by rotating on itself a transverse shaft, traversing the section of secondary duct, and parallel to the pivot axis of the valve element. But, preferably, the link arm assembly is actuated by an overlength travel actuator, preferably a rotary cylinder, which, in the first position of the valve element, holds the valve element pressed with force by its machined bearing surface against the machined seat of the section of secondary duct. In this case, advantageously, the actuator is a rotary cylinder rotating on itself the drive shaft of the link arm assembly and is mounted laterally outside the section of secondary duct, which shelters the actuator from the possibly corrosive gas flow on the one hand, and, on the other hand, makes it easier to protect, where appropriate, from an ambient magnetic field, for example by a Faraday cage for protecting an electrovalve for controlling a rotary cylinder with operating fluid, when, for example, the device is used close to aluminium electrolysis tanks in which electrodes are supplied with electric current of a very high voltage. In order, all at the same time, to facilitate the linking of the link arm assembly and the valve element, and to stiffen the latter, the valve element is - 13 advantageously stiffened by at least two ribs parallel with one another, and between which is articulated a link arm of the link arm assembly for operating the valve element, in which case the sealed bearing surface of the valve element is machined after the ribs are welded onto the valve element and, where necessary, after the trunnions or a pivot shaft are welded onto the bent edge of the valve element. Brief Description of the Drawings Further features and advantages of the invention will now be described in a non-limiting way, with reference to the accompanying description and drawings, in which: Figure 1 is a plan view of a gas flow diversion device with a single valve element according to an embodiment of the invention, Figure 2 is a view in cross-section along II-II of Figure 1, and Figure 3 is a view in longitudinal mid-plane section along III-III of Figure 1. Best Mode(s) for Carrying Out the Invention The gas flow diversion device according to Figures 1 to 3 comprises a section of primary duct 1, which is rectilinear and tubular of quadrangular and constant cross-section from its entrance 2 to its exit 3 (respectively on the right and on the left of Figures 1 and 3) delimited by peripheral attachment flanges 4 and 5, projecting outwards perpendicular to the longitudinal and central axis AA of the section of primary duct 1, for the sealed connection of the entrance 2 and exit 3 respectively to the upstream and downstream portions of a primary air flow circuit (not shown) for circulation of a gas flow which may be hot, dusty and/or contain dangerous even toxic elements.

- 14 In this example, the section of primary duct 1 is a horizontal section of square cross-section of which two sides are oriented vertically along the height and the two other sides horizontally along the width of the section of primary duct 1. The diversion device also comprises a section of secondary duct 6 which is also rectilinear and tubular of quadrangular cross-section, also square in this example, and whose exit 8 is intended to be connected in sealed manner to a secondary air flow circuit, via a peripheral exit flange 9 projecting outwards from the section 6 perpendicular to its longitudinal and central axis BB. In this example, this section of secondary duct 6 has its longitudinal axis BB oriented vertically and its entrance 7 opens into the flat top wall 10 of the section of primary duct 1. In practical manner, the entrance 7 of the section of secondary duct 6 is delimited by the upstream edges (the bottom edges on Figures 2 and 3) of the four flat walls of this section 6, that is to say the upstream wall 11 and downstream wall 12 of the section 6, relative to the direction of discharge of the gas flows in the section of primary duct 1, from its entrance 2 to its exit 3, and the two side walls 13 and 14 of the section 6, the assembly being thus arranged so that the upstream end portions of these four walls 11, 12, 13 and 14 protrude inside a vertical shallow compartment 15, arranged to project above the top wall 10 of the section of primary duct 1, as shown in Figures 2 and 3. This compartment 15 is delimited by an upstream wall 16 and a downstream wall 17 which are portions of the top wall 10 bent vertically upwards, and by the top end portions 18 and 19 of the flat side walls 20 and 21 of the section of primary duct 1.

- 15 The dimensions of the compartment 15 and of the section of secondary duct 6 are such that the walls 11 and 12 of the section 6 are spaced respectively downstream and upstream of the walls respectively upstream 16 and downstream 17 of the compartment 15, while the side walls 13 and 14 of the section 6 are nested inside the side walls 18 and 19 of the compartment 15 and in contact with the latter, the engagement of the section 6 along its axis BB in the compartment 15 being such that the entrance 7 of this section 6 is an opening delimited by the upstream edges of the four walls 11, 12, 13 and 14 of the section 6, and situated in the plane of the top wall 10 of the section 1. The sections of duct 1 and 6 are secured in this position by a peripheral flange 22, projecting outwards around the section 6 and bolted, with interposition of a seal, for example made of silicon, on the flaps 23, 24, 25 and 26 respectively of the walls 16, 17, 18 and 19 of the compartment 15, these flaps being bent outwards. The diversion device further comprises a valve element 27, or flag damper, of rectangular shape, whose short sides are oriented horizontally and transversely and define the width of the valve element 27, which is slightly less than the distance between the side walls 20 and 21 of the section of primary duct 1, while the length of the valve element 27 is greater than the distance separating the walls 11 and 12 of the section of secondary duct 6, and this valve element 27 is mounted pivotingly in the section of primary duct 1, about a horizontal and transversal geometric axis XX, by one of its edges 28, extending along the width, and substantially bent at right angles to the rest of the valve element 27. Along the free end of its bent edge 28, the valve element 27 is secured to a pivot shaft 29, whose two ends, each turned towards one respectively of the two side walls 18 and 19 of the compartment 15, constitute - 16 the cylindrical trunnions 30 of circular section and coaxial about the geometric pivot axis XX, each of which is mounted pivotingly, with a slight radial clearance relative to the geometric axis XX, in one respectively of two bearings 31 coaxial and secured to the section of secondary duct 6, downstream (relative to the direction of discharge of the gas flows in the section of primary duct 1) of the downstream wall 12 of this section 6. In this example, each of the two bearings 31 consists of a lateral side plate secured to the downstream face of the bottom end portion of the downstream wall 12 of the section 6, so as to project into the housing, delimited immediately downstream of the wall 12 of the section 6, between this wall 12 and the downstream wall 17 of the compartment and beneath the flange 22, as is clearly shown in Figure 3. In this housing, each of the side plates 31 extends substantially parallel to the side walls 18 and 19 of this housing, and has an oblong opening 32 into which one respectively of the two trunnions 30 is engaged with some radial clearance. In this example, the oblong opening 32 of each bearing side plate 31 is delimited by the two branches of a U shaped side plate 31 on its side pointing downstream of the section of primary duct 1, therefore open towards the downstream wall 17 of the compartment 15 and of the housing that receives the pivot articulation of the valve element 27. Thus, the valve element 27 is mounted pivotingly, in the section of primary duct 1, substantially with sealing between its edges perpendicular to its pivot shaft 29 and the side walls 20 and 21 facing the section of duct 1, due to the limited clearance between these edges and these walls so as not to block the pivoting of the valve element 27, which pivots between two extreme positions, a first of which, wherein the - 17 valve element 27 is represented in section (and therefore hatched) in Figures 2 and 3 is a so-called normal position or "open" towards the primary air flow circuit, in which the valve element 27 is pressed against the upstream edges, delimiting the entrance opening 7 of the section of secondary duct 6, of the walls 11, 12, 13 and 14 of this section 6, so as to close this entrance 7 in order that the gas flow discharges from the entrance 2 to the exit 3 of the section of primary duct 1. The second position of the valve element 27 is a position of closure of the primary air flow circuit, in which the valve element, identified by the reference number 27a in Figure 3, is moved away from the entrance 7 of the section of secondary duct 6 and pivoted until its free transverse edge 33, opposite its curved pivoting edge 28, is pressing, as indicated at 33a in Figure 3, against the bottom wall 34 of the section of primary duct 1, in substantially sealed manner, such that the gas flow entering via the entrance 2 of the section of primary duct 1 is diverted by the valve element in its position 27a towards the entrance 7 of the section of the secondary duct 6. Because of the rectangular shape of the valve element 27 and of its length relative to the height of the section of primary duct 1, in the position of closure of the primary air flow circuit, the valve element 27a (see Figure 3) is inclined at an angle P relative to its "open" position, in which the valve element 27 closes the entrance 7 of the section of secondary duct 6, and its free edge 33a, pressing against the bottom wall 34, is axially upstream, in the section 1, of the pivot shaft 29 and of the trunnions 30 of the other bent transverse edge 28 of this valve element 27. To ensure, in the "open" position, a practically sealed closure of the entrance 7 of the section of secondary duct 6, the valve element 27 has, on its face (top face - 18 in Figure 3) which is turned towards the section of secondary duct 6, a square and machined annular bearing surface 35, for a sealed pressure against a seat 6a formed by machining of the upstream edges (bottom edges in Figures 2 and 3) of the walls 11, 12, 13 and 14 of the section 6 against which the valve element 27 presses in its position of closure of the entrance 7 of this section 6. A good sealed pressure of the valve element 27 via its square and machined bearing surface 35 against the machined seat 6a at the upstream end of the section of secondary duct 6 is possible due to the limited radial clearance with which the trunnions 30 of the curved edge 28 of the valve element 27 are each mounted in the oblong opening 32 of the corresponding U-shaped bearing side plate 31. Figure 3 shows schematically at 35 the two transverse sides of the machined annular and square bearing surface on the valve element 27, this bearing surface 35 being able to be machined on an annular and square boss projecting on the face of the valve element 27 turned towards the section of secondary duct 6, or, on the contrary, machined on the bottom of a square annular spot facing made in this face of the valve element 27. Due to the interaction of the pivot shaft 30 mounted swivelling with radial clearance in the two bearings 31 and the machined bearing surface 35 for the valve element 27 to press against the machined seat 6a on the upstream end of the section of secondary duct 6, (relative to a diverted discharge along the axis BB of this section 6), in normal position, that is to say when the valve element 27 closes the opening 7 for entrance of the section of secondary duct 6, it can be defined that at the minimum 99% of the gas flow passing through the entrance 2 of the section of primary duct 1 is directed to its exit 3, towards the primary air flow circuit, and at the maximum 1% of this flow may be - 19 diverted via the secondary air flow circuit, through the section of secondary duct 6, due to residual leaks around the valve element 27, and due to the fact that the secondary air flow circuit may be at a different pressure from that of the primary air flow circuit. In the so-called "closed" position, that is to say in the position 27a of the valve element, at the minimum 98% of the gas flow exiting via the exit 8 of the section of secondary circuit 6 originates from upstream of the entrance 2 of the section of primary circuit 1 by diversion in the device, and at the maximum 2% of this flow may return from downstream of the primary air flow circuit, via the exit 3 of the section of primary duct 1, and discharge into the section of secondary duct 6 due to leaks around the valve element 27. In the "closed" position, in which the valve element 27 in position 27a closes the access of the gas flow to the primary circuit, a relatively significant discharge of gas coming from downstream of the primary circuit, under the effect of the pressure difference between the secondary and primary circuits, may occur at the bent edge 28 and the pivot shaft 30 of the valve element 27. This discharge of gas is eliminated by the installation of a metal sealing flap 36, elastically deformable, also called foil, which is preferably made with the aid of a flat rectangular piece of spring steel, attached along one of its transverse marginal portions 37 against the bottom face of the top wall 10 of the section of primary duct 1, downstream of the housing in which the bent edge 28 of the valve element 27 is mounted pivotingly, while the other, opposite marginal portion 38 is elastically pressing slidingly against the valve element 27, irrespective of the angle taken by the valve element 27 in closure position. As a variant, and depending on the pivot angle B of the valve element 27, it is possible to attach the flap 36 by its margin portion 38 onto the valve element 27, and - 20 the flap 36 presses elastically and slidingly by its opposite marginal end 37 against the internal face of the top wall 10 of the section of the primary duct 1. To operate the movements of the valve element 27 from one position to the other, the diversion device also comprises an operating link arm assembly 39 comprising an assembly with link arm 40 and handle 41, able to be operated manually, but preferably driven by an actuator 42, such as a rotary cylinder, providing an overlength travel in order to keep the valve element 27 pressed with force against its machined seat 6a at the upstream end of the section of secondary duct 6 projecting into the compartment 15 and delimiting the entrance 7 of this section 6. The rotary cylinder 42 is attached, as can be seen in Figures 1 and 2, laterally on the outside of the side wall 13 of the secondary section 6, and, by means of its output shaft 43, it rotates on itself a transmission shaft 44, parallel to the pivot axis XX of the valve element 27, and which traverses the section of secondary duct 6, in the two side walls 13 and 14 of which this transverse shaft 44 is mounted pivotingly. Substantially in the middle of the transverse shaft 44, the latter is secured in rotation with one end of the handle 41, whose other end is articulated pivotingly about a shaft 46 substantially parallel to the shaft 44 and to the shaft XX for pivoting the valve element 27, on one end of the link arm 40, whose other end is articulated on the valve element 27. Thus, the shaft 44, rotated by the rotary cylinder 42, itself rotates the handle 41, which moves the link arm 40 so as to operate the valve element 27 from one to the other of its two extreme positions of movement. For this purpose, the rotary cylinder 42 is reversible. In this configuration, the link arm assembly 39 and the - 21 drive shaft 44 are mounted in the section of secondary duct 6, the link arm assembly 39 occupying even substantially the central portion of this section 6, so as to exert its action substantially in the centre of gravity of the valve element 27 in order to further improve the sealing pressure of the valve element 27 against its seat 6a. For this, the link arm 40 is articulated on the valve element 27 while being mounted pivotingly, about a transverse shaft 47, parallel to the pivot axis XX of the valve element 27 and to the axes of the transverse shaft 44 and of the articulation 46 of the link arm 40 on the handle 41, between two ribs 45 parallel with one another and welded to the face of the valve element 27 which is turned towards the section of secondary duct 6, in order to stiffen the valve element 27. As shown in Figure 2, the two ribs 45 may consist of two flanges of a length of U section welded onto the valve element 27. In this embodiment, the welding of the ribs 45 and of the trunnions 30 and/or of the pivot shaft 29 on the valve element 27, made out of metal sheet, must occur before the machining of the annular and quadrangular bearing surface 35 for pressing this valve element 27 sealingly against the sealed seat 6a machined at the upstream end of the four walls 11, 12, 13 and 14 of the section of secondary duct 6. Concerning the link arm assembly 39, note that it is preferable that the point of action of the transverse drive shaft 44 on the handle 41 is situated, in the direction along the axis XX of the section of primary duct 1, between the pivot axis XX of the valve element 27 and the point of action of the link arm 40 on the valve element 27, substantially on the shaft 47 of articulation of the handle 40 on the ribs 45, while in the axial direction along the axis BB of the section of secondary duct 6, the point of action of the rotary shaft 44 on the handle 41 is shifted downstream, in the - 22 section of secondary duct 6, relative to the point of action of the link arm 40 on the valve element 27 in the position of closure of the section of secondary duct 6. This configuration has numerous advantages. In particular, the link arm assembly 39 and the drive shaft 44 are scoured by the gas flow only in the "closed" position of the valve element 27a, in which the gas flow is diverted towards the secondary air flow circuit, a situation which occurs, in the applications envisaged, less frequently and for less time than the situation in which the valve element 27 is in the "open" position, in which it closes the section of secondary duct 6. Furthermore, all of the link arm assembly 39, its drive shaft 44 and the actuator 42, plus the assembly of the valve element 27 and its pivot articulation are, in this example, mounted on the section of secondary duct 6, which, thus equipped, is merely partially engaged and attached thereafter in and on the section of primary duct 1. The tricky operations of assembly, welding and machining are thus combined on elements which are all mounted on the section of secondary duct 6, which considerably simplifies the production of the section of primary duct 1, and makes it possible to reduce the production and maintenance costs of the diversion device. Furthermore, the cross-section of the two sections 1 and 6 of the device is such that the particles and dust conveyed cannot accumulate or settle in the zone of action of the valve element 27. It is understood that the positioning of the link arm assembly 39 may be optimized as a function of the length of the valve element 27 and of its angle of rotation P between its two extreme positions. However, the use of this link arm assembly 39 and its positioning substantially mid-way along the length of - 23 the valve element 27 make it possible to ensure a better placement of the valve element 27 against its seat, in the position of closure of the section of secondary duct 6, and less force for the operation and maintenance in tension of the valve element against its seat is required. According to the design and installation constraints, the angle a between the sections of primary duct 1 and secondary duct 6, therefore the angle between the axes AA and BB of these two sections, oriented from upstream to downstream, and therefore also the angle of the corresponding gas flows, may preferably vary between 300 and 1200, and more preferably between 300 and 900, the latter value of the angle a being that which corresponds to the embodiment in Figures 1 to 3. This angular range is preferred in order not to increase in too great a degree the loss of pressure created by the gas flow diversion "elbow". Consequently, when the angle a lies between approximately 850 and approximately 1200, the maximum angle P, in which the valve element is in the position 27a blocking off the section of primary duct 1, is preferably 850, while for an angle a lying between approximately 300 and approximately 850, the angle 3 of the valve element 27 may be chosen at the maximum to be equal to the angle a and at the minimum to be equal to 0.35 a. In other words, when a lies between 300 and 850, the angle P lies between a and 0.35 a, whereas when a lies between 850 and 1200 the angle P is at the maximum of 850. More generally, for a given angle a chosen in an angular range extending from 300 to 1200, and preferably from 300 to 900, the angle f is advantageously chosen so that the pressure losses in the diverted gas flow, when the valve is in position 27a blocking the section of primary duct 1, are minimal. If they are not the lowest, and according to the installation constraints, the angle P may be chosen - 24 so that the pressure losses are as close as possible to their minimum value. Relative to the axis AA of the section of primary duct 1, the section of secondary duct 6 may be oriented 3600 about the axis AA, according to the constraints created by the surrounding installation. However, the seal and mobility of the valve element 27 are greatly influenced and helped if the axis XX of rotation of the valve element 27 is horizontal, as shown in Figures 1 to 3. In a particular exemplary embodiment, the diversion device according to the invention may be used in aluminium electrolysis workshops, or in similar applications, producing hot gases that have to be discharged for filtration and/or neutralization processes in order to scrub them. Specifically, these gases may, where appropriate, contain dangerous, even toxic, constituents and/or be filled with harmful dust, so that they cannot be placed in the atmosphere without a prior scrubbing treatment. Furthermore, the temperature of these gases may exceed 2000C. It is therefore necessary to confine these gases and ensure that they are discharged into a centralized treatment system. For this, the tanks in which these gases are generated are covered in sealed manner and fitted with conventional intake pipes. The intake circuits of several tanks are combined as a function of the volumes of gas to be extracted, volumes which are conveyed towards a treatment and scrubbing/cooling assembly, at the outlet of which the gases are discharged into the atmosphere. Conventionally, in aluminium electrolysis workshops, gas flows of more than one million m 3 /h are extracted and treated by filtration and scrubbing. Since these workshops operate continuously, there is no question of waiting or totally shutting down the plant to carry out certain periodic maintenance or service operations, or yet when there are incidents. To carry out these operations, the sealed cover for confining - 25 one or more tanks must be opened, which considerably changes the intake conditions on this or these tanks, and may equally lead to disruption of the intake conditions of the other tanks connected to the same intake and treatment system such that, overall, conditions of discharging into the atmosphere may be created which are outside the normative limits or those set for the plant in question. Accordingly, "double intake" or "on intake" plants have already been provided that make use of a second, additional intake system acting on each of the tanks. In the event of a service or maintenance operation on a given tank, the intake of the gases of this tank is diverted to the "on intake" system, and the main intake pipework is isolated from this tank by a flow diversion device, of the type according to the present invention, in order not to disrupt the intake conditions on the other tanks, in operation, belonging to the same treatment and scrubbing circuit. Thus, although, in the normal or primary circuit, intake is carried out by one or more pumping-out fans placed downstream of the treatment system, in the "on intake" circuit, intake is carried out by a fan (also called a booster) which creates a forced intake and into which go untreated gases which are then reinjected into the normal circuit just before the gas scrubbing treatment unit. Thus, due to the use of gas flow diversion devices of the type according to the present invention, it is possible to isolate a tank under maintenance or for a particular service operation without unbalancing the main air flow circuit, while maintaining an effective intake on that tank via the secondary air flow circuit. Furthermore, the two air flow circuits (primary and secondary or auxiliary) do not leak from one to the - 26 other, which is extremely important. Specifically, since the tanks are installed in parallel and where necessary in large numbers (possibly reaching 350 tanks), if the valve element of each of the gas flow diversion devices used allows a leakage of a few percent, in "open" position, then the secondary air flow circuit must absorb the total of these leakages, which may represent a considerable flow, taking into account the number of tanks. On the other hand, in "closed" position and even if the sealing remains an important criterion in the valve element, a leak from the primary air flow circuit to the secondary air flow circuit is less inconvenient, since only a few tanks are simultaneously connected to the secondary air flow circuit (because of undergoing service or maintenance operations), so that the total of any leaks to be absorbed by the secondary air flow circuit is much smaller. It is evident that the gas flow diversion device according to the invention is particularly suitable for such uses. Modifications and variations such as would be apparent to a skilled addressee are deemed to be within the scope of the present invention. Throughout the specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers. Furthermore, throughout the specification, unless the context requires otherwise, the word "include" or variations such as "includes" or "including", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other - 27 integer or group of integers. Additionally, throughout the specification, unless the context requires otherwise, the words "substantially" or "about" will be understood to not be limited to the value for the range qualified by the terms.

Claims (16)

1. A diversion device for diverting a gas flow between a primary air flow circuit and a secondary air flow circuit, the gas flow being hot and/or filled with dust and/or including at least a dangerous even toxic component, the diversion device comprising: a section of a primary duct, rectilinear and tubular of quadrangular cross-section, having an entrance and an exit to be connected to the primary air flow circuit, a section of a secondary duct, rectilinear and tubular of quadrangular cross-section, having an entrance which opens into one of four walls of the section of the primary duct and an exit to be connected to the secondary air flow circuit, a valve element, of quadrangular shape, mounted pivotably substantially along the length of one of its edges in the section of the primary duct about a pivot axis transverse to the wall between a first position and a second position, wherein the first position is a position of opening towards the primary air flow circuit in which the valve element closes the entrance of the section of the secondary duct, and the second position is a position of closure of the primary air flow circuit in which the valve element is pivoted away from the entrance of the section of the secondary duct so as to prevent the gas flow from discharging through the exit of the section of the primary duct and divert the gas flow entering via the entrance of the section of the primary duct towards the section of the secondary duct, and a link arm assembly connected to the valve element in order to operate the valve element to pivot between the first and second positions, wherein the valve element has, on a face facing the section of the secondary duct when in the first position, a machined quadrangular annular bearing - 29 surface to press in sealed manner against a machined seat of an edge of the section of the secondary duct delimiting the entrance of the section of secondary duct, the valve element being mounted pivotably with a limited radial clearance relative to the pivot axis, and wherein when the valve element is in the second position, an opposing edge of the valve element opposing the pivoting edge is resting against an opposing wall of the section of the primary duct opposing the wall of the section of the primary duct into which the section of the secondary duct opens, and two opposing edges of the valve element which are perpendicular to the pivoting edge have a limited clearance with respective opposing walls of the section of primary duct so as not to block the pivoting actions of the valve element between the first and second positions, wherein the pivoting edge of the valve element is bent preferably substantially at right angle to the rest of the valve element and secured, at its lateral ends, to two coaxial cylindrical trunnions of circular cross-section, each pivoting with some radial clearance to respective one of two coaxial bearings secured to at least one of the sections of the primary and secondary ducts, and wherein at least one of the two bearings is formed by a lateral side plate secured to at least one of the two sections of the primary and secondary ducts, the side plate has a round or oblong opening in which is engaged, with radial clearance, respective one of the two trunnions.

2. A diversion device for diverting a gas flow between a primary air flow circuit and a secondary air flow circuit, the diversion device comprising: a section of a primary duct having an entrance and an exit to be connected to the primary air flow circuit, a section of a secondary duct having an entrance - 30 which opens into a wall of the section of the primary duct and an exit to be connected to the secondary air flow circuit, a valve element mounted pivotably along one of its edges in the section of the primary duct about a pivot axis transverse to the wall between a first position and a second position, wherein the first position is a position of opening towards the primary air flow circuit in which the valve element closes the entrance of the section of the secondary duct, and the second position is a position of closure of the primary air flow circuit in which the valve element is pivoted away from the entrance of the section of the secondary duct so as to prevent the gas flow from discharging through the exit of the section of the primary duct and divert the gas flow entering via the entrance of the section of the primary duct towards the section of the secondary duct, and a link arm assembly connected to the valve element in order to operate the valve element to pivot between the first and second positions, wherein the valve element has, on a face facing the section of the secondary duct when in the first position, a machined bearing surface to press in sealed manner against a machined seat of an edge of the section of the secondary duct delimiting the entrance of the section of secondary duct, the valve element being mounted pivotably with a limited radial clearance relative to the pivot axis, and wherein when the valve element is in the second position, an opposing edge of the valve element opposing the pivoting edge is resting against an opposing wall of the section of the primary duct opposing the wall of the section of the primary duct into which the section of the secondary duct opens, and two opposing edges of the valve element which are perpendicular to the pivoting edge have a limited clearance with respective opposing walls of the section of primary duct so as not to block the pivoting actions of the valve element between the first and - 31 second positions, wherein the pivoting edge of the valve element is bent preferably substantially at right angle to the rest of the valve element and secured, at its lateral ends, to two coaxial cylindrical trunnions of circular cross-section, each pivoting with some radial clearance to respective one of two coaxial bearings secured to at least one of the sections of the primary and secondary ducts, and wherein at least one of the two bearings is formed by a lateral side plate secured to at least one of the two sections of the primary and secondary ducts, the side plate has a round or oblong opening in which is engaged, with radial clearance, respective one of the two trunnions.

3. The diversion device according to Claim 2, wherein the gas flow is hot and/or filled with dust and/or including at least a dangerous even toxic component.

4. The diversion device according to Claim 2 or 3, wherein the section of the primary duct and/or the section of the secondary duct is rectilinear and tubular of quadrangular cross-section.

5. The diversion device according to any one of Claims 2 to 4, wherein the wall of the section of the primary duct is one of four walls of the section of the primary duct.

6. The diversion device* according to any one of Claims 2 to 5, wherein the valve element is of quadrangular shape and is mounted pivotably substantially along the length of the pivoting edge. - 32

7. The diversion device according to any one of Claims 1 to 6, wherein at least one of the two bearings is formed by a lateral, U-shaped side plate, open in the downstream direction of the section of the primary duct, and the at least one of the two bearings is formed in a housing directly adjacent and downstream to a downstream edge of the entrance of the section of the secondary duct and adjacent an opening in the wall of the section of the primary duct in which the entrance of the section of the secondary duct is made, wherein said downstream is relative to the direction of discharge of the gas flows in the primary duct from its entrance to its exit.

8. The diversion device according to any one of Claims 1 to 7, wherein the diversion device further comprises an elastically deformable metal sealing flap, preferably made of flat spring steel, of substantially quadrangular form, connected along one of its marginal portions to the wall of the section of the primary duct into which the entrance of the section of the secondary duct opens, at a portion downstream of the entrance relative to the direction of discharge of the gas flows in the primary duct from its entrance to its exit, or to the valve element, and the opposite marginal portion is elastically pressing slidingly against the valve element, or against the wall of the section of the primary duct into which the section of secondary duct opens, at a portion downstream of the pivoting articulation of the valve element, wherein said downstream is relative to the direction of discharge of the gas flows in the primary duct from its entrance to its exit.

9. The diversion device according to any one of Claims 1 to 8, wherein, if at is the angle between the axes of the two sections of the primary and secondary ducts oriented from upstream to downstream, the valve - 33 element in the second position is pivoted, from the first position, through a maximum angle B limited to 85* or to the angle a, depending on whether the angle a is greater than 850 and less than 1200 or lying between 300 and 850, and, in the latter case, the minimum angle P is equal to 0.35 a, and wherein said downstream and upstream are relative to the direction of discharge of the gas flows in the primary duct from its entrance to its exit.

10. A diversion device according to any one of Claims 1 to 9, wherein, for a given angle a, between the axes of the two sections of the primary and secondary ducts oriented from upstream to downstream, and chosen in an angular range extending from 300 to 1200, and preferably from 300 to 900, the angle P of pivot of the valve element from the first to the second position is chosen such that the pressure losses in the diverted gas flow, when the valve element is in the second position, are minimal, and wherein said downstream and upstream are relative to the direction of discharge of the gas flows in the primary duct from its entrance to its exit.

11. A diversion device according to any one of Claims 1 to 10, wherein the link arm assembly comprises a link arm and a handle, the link arm assembly is mounted substantially in the central portion of the section of the secondary duct and exerts its action substantially on the centre of gravity of the valve element.

12. A diversion device according to Claim 11, wherein the link arm assembly is driven by rotating a transverse shaft, traversing the section of the secondary duct and parallel to the pivot axis of the valve element.

13. A diversion device according to any one of Claims 1 to 12, wherein the link arm assembly is actuated by - 34 an overlength travel actuator, preferably a rotary cylinder, which, when the valve element is in the first position, holds the valve element such that the machined bearing surface is pressed with force against the machined seat of the section of the secondary duct.

14. A diversion device according to Claim 13, when dependent from Claim 7, wherein the actuator is a rotary cylinder which rotates the drive shaft of the link arm assembly and is mounted laterally outside the section of the secondary duct.

15. A diversion device according to any one of Claims 1 to 14, wherein the valve element is stiffened by at least two ribs parallel with one another, and between which a link arm of the link arm assembly for operating the valve element is articulated.

16. A diversion device substantially as hereinbefore described with reference to the accompanying drawings.