Title of Invention

PRESSURE COOKER WITH MANHOLE WITH AN OVERPRESSURE SAFETY DEVICE

Abstract

Pressure cooker with manhole with an overpressure safety device, comprising a cooking chamber (1), with an oval opening bordered by a re-entrant rim (4) in which an oval lid (10) is able to be inserted, defining a small diameter (d) and a large diameter (D), in order to hermetically close the chamber (1) by means of a sealing joint (11) which is mounted in a peripheral groove (12) in the lid (10) forming a rolled edge (13) and defining an internal face (13A) and an external face (13B), the said joint thus coming into sealed abutment against the re-entrant rim (4), characterised in that, in the area (S) corresponding to the large diameter (D) of the lid (10), the groove (12) comprises creep means (20, 21) for the joint (11), and in that the joint (11), the re-entrant rim (4) and the lid (10) are formed so that, in the event of overpressure, the lid (10) being in a position of abutment against the re-entrant rim (4) through the periphery of the rolled edge (13), the joint (11) creeps locally through the creep means (20, 21) in a centripetal manner under the effect of the pressure acting through the creep means in order to break the seal locally and allow the steam to escape between the re-entrant rim (4) and the lid (10).

Full Text

FORM 2 THE PATENTS ACT 1970 [39 OF 1970] & THE PATENTS RULES, 2003 COMPLETE SPECIFICATION [See Section 10; rule 13] "PRESSURE COOKER WITH MANHOLE WITH AN OVERPRESSURE SAFETY DEVICE" SEB S.A., of Les 4M, Chemin du Petiti-Bois, Boite Postale 172, F-69132 Ecully Cedex, France, The following specification particularly describes the invention and the manner in which it is to be performed: The present invention relates to a pressure cooker with manhole with an overpressure safety device. The present invention relates to the technical field of safety pressure-release devices for manhole type pressure cookers by breaking the seal provided by means of the pressure cooker gasket, such devices being designed to prevent steam squirting out violently and/or to prevent total destruction of the cooking appliance in the event of the pressure becoming too high. The present invention relates to a safety pressure-release device for a manhole pressure cooker comprising a cooking vessel with an oval opening defined by a "reentrant rim in which an oval lid can be inserted, the oval defining a minor diameter and a major diameter, the lid serving to close the vessel hermetically via a sealing gasket mounted in a substantially peripheral groove of the lid which forms a rolled edge defining an inner face and an outer face, said gasket thus coming to bear in leaktight manner against the reentrant rim. The present invention also relates to a sealing gasket for mounting on a manhole type pressure cooker of the invention. PRIOR ART So-called "manhole" type pressure cookers, also known as reentrant lid type pressure cookers, are well known and present certain advantages, in particular advantages relating to being simple and inexpensive to manufacture, thus enabling appliances to be made that are particularly simple and low in cost. As is well known to -the person skilled in the art, manhole pressure cookers are pressure cookers in which the vessel and the lid are generally oval in shape, enabling the lid to be inserted into the vessel so that once it has been put into the vessel and turned, the lid can be brought to occupy a position in which it seals the vessel in leaktight manner via a sealing gasket, with the rolled edge of the lid being inside the vessel and with the sealing gasket being interposed between the rolled edge of the lid and the reentrant peripheral edge of the vessel. It is already known to fit manhole pressure cookers with safety pressure-release devices, and the best known safety pressure-release devices' in the most widespread use are generally constituted a fusible safety plug. This is generally constituted by a piece or pellet of thermoplastic material fixed to the lid, e.g. by screw engagement. In the event of temperature and pressure rising . abnormally, the pellet or piece of thermoplastic material,is caused to melt whereupon it is ejected from the lid, thus enabling the excess pressure to escape. The thermoplastic material pieces can be replaced by fusible safety plugs made using pieces of metal that melt easily. Presently known systems using a fusible safety plug do not perform their safety function as well as they should, and they suffer from certain drawbacks. In particular, it has been found that when the pellet is ejected, a relatively large amount of steam sguirts out, which is potentially dangerous because of the speed at which the fusible plug is triggered and the absence of any protection above the pressure cooker. Furthermore, it turns out that the temperature and pressure level at which a fusible plug is triggered is excessively variable, thereby reducing the effectiveness and the safety provided by such devices. Furthermore, it has also been found that the trigger pressure of such safety devices is generally rather low, which is harmful to their effectiveness since some users, on finding out that those safety devices are triggered every time the cooker is used dry unintentionally, tend to get rid of the safety device by replacing the fusible plugs with a nail or a. piece of metal so as to obtain an appliance that has no safety device at all. In the absence of a safety system, manhole pressure cookers can become extremely dangerous because, when the pressure rises excessively, such cooking appliances are destroyed by exploding, which makes them excessively dangerous even though because of their low cost they are extremely widespread in certain regions of the world. In the present Applicants' prior French patent . application FR 99/09758, yet to be published, the entire description of which is fully incorporated in the present application, proposals have already been made to provide a manhole pressure 'cooker with a safety device using means that enable the gasket to. leak in the event of pressure rising excessively. The present patent application constitutes a technical development of that as yet unpublished prior application. SUMMARY OF THE INVENTION Consequently, the objects given to the invention seek to remedy the various drawbacks listed above and to propose a novel safety pressure-release device for a manhole pressure cooker that makes it possible to achieve good control and good repetitivity of the movement of the gasket that provides sealing while avoiding destruction of the appliance in the event of excess pressure. Another object of the invention seeks to propose a novel safety pressure-release device enabling the gasket to be deformed and leakage to be set up locally by means that are particularly simple and reliable. Another object of the invention seeks to propose a novel safety pressure-release device providing increased safety by using a second safety level capable of coming into operation in the event of the first safety level failing to operate. Another object of the invention seeks to propose a novel safety pressure-release device providing excellent effectiveness in terms of safety while being of particularly simple design. Another object of the invention seeks to propose a novel safety device avoiding any risk of mishandling, modification, or wrong assembly of the elements that make it up. The objects assigned to the invention are achieved by a safety pressure-release device for a manhole pressure cooker comprising a cooking vessel with an oval opening defined by a reentrant rim in which an" oval lid can be inserted, the oval defining a minor diameter and a major diameter, the lid serving to close the vessel hermetically via a sealing gasket mounted in a substantially peripheral groove of the lid which forms a rolled edge defining an inner face and an outer face, said gasket thus coming to bear in leaktight manner against the reentrant rim, the safety pressure-release device being characterized in that, substantially in the zone corresponding to the major diameter of the lid, the ' groove includes creep-inducing means for causing the gasket to creep, and in that the gasket, the reentrant rim, and the lid are shaped in such a manner that in the event of excess pressure, while the lid is in abutment against the reentrant rim via the periphery of the rolled edge, the gasket is caused to creep locally by the creep-inducing means in centripetal manner under the effect of the pressure acting via the creep-inducing means to cause sealing to be broken locally and to allow steam to escape between the reentrant rim and the lid. BRIEF SUMMARY OF THE ACCOMPANYING DRAWING The objects assigned to the invention are explained in greater detail on reading the following description made with reference to the accompanying drawings that are given purely by way or non-limiting illustration and in which: - Figure 1 is an overall perspective view of a manhole pressure cooker in accordance with the' invention; - Figure 2 is an overall cross-section view of a manhole pressure cooker in accordance with the invention; - Figure 3 is a perspective view showing a detail of the lid of a manhole pressure cooker in accordance with the invention; - Figure 4 is a perspective view of a manhole pressure cooker lid in accordance with the invention including a sealing gasket in accordance with the invention; - Figure 5 is an overall perspective view of a sealing gasket in accordance with the invention; Figures 6 and 7 are fragmentary section views showing the general principle whereby the gasket of the invention is moved; and - Figure 8 is a plan view of a preferred variant of a gasket in accordance with the invention. BEST MANNER OF PERFORMING THE INVENTION Figure 1 is a general view of a manhole pressure cooker comprising a cooking vessel 1 made of a metal, having a bottom 2 from which the substantially vertical side walls 3 of the vessel project upwards, said side walls being surmounted by a reentrant edge 4 extending around the entire periphery of the vessel 1. The opening in the vessel is substantially oval in shape, being defined by the end edge 5 of the reentrant rim 4 . As is well known to the person skilled in the art, the reentrant rim 4 in the meaning of the invention means the annular top end portion of the vessel 1 that extends towards the axis' of symmetry A of the vessel, regardless of the angle at which the reentrant rim 4 extends relative to a horizontal plane, the reentrant rim 4 thus overlying a portion of the bottom 2. The manhole pressure cooker of the invention also has a lid 10 (Figure 4) of likewise substantially oval shape with a domed central portion 10A and a frustoconical flank 10B, the lid 10 being designed to be inserted through the opening of the cooking vessel 1 so as to enable it to be closed hermetically by means of a sealing gasket 1 1 mounted in a substantially peripheral groove 12 of said lid 10, said groove being formed by a rolled edge 13. By means of this disposition, with the gasket 1.1 placed to bear against the bottom of the groove 12, the lid 10 can be inserted through the opening of the vessel 1 by means of a handle 26 by tilting the lid slightly and inserting it via the major axis of the opening of the vessel, after which the oval shape of the lid 10 can be brought into coincidence with the' oval shape of the vessel 1 by turning the lid through an angle of about 90°. In the closed position shown in Figure 2, the lid 10 is held against the reentrant rim 4 via the top portion of the gasket 11 which presses in leaktight manner against the reentrant rim 4, this being ensured by a handle 27 of the vessel being engaged with the handle 26 of the lid. As shown in Figure 1, the lid handle 16 is fixed by a rod 28 to the lid 10 extending along a radius corresponding to the major diameter D of the lid 10. As can be seen particularly well in Figures 6 and 7, the groove 12 defined on the outside by the rolled edge 13 has an inside face 13A and an outside face. 1 3B forming the rolled edge proper which is to come to bear against the inside face of the reentrant rim 4 via its top end 13C as shown in Figure 3, in the event of the pressure rising excessively. In the abutment position as shown in Figure 7, the rolled edge 13 comes into abutment via one or more angular sectors, depending on its geometrical shape, each sector being defined by its top end surface 13C. In the invention, the gasket 11 and the reentrant rim 4 are shaped so that in the event of the pressure rising excessively, the lid 10 comes into its abutment position against the reentrant rim 4 via one or more sectors of the periphery of the rolled edge 13, 13B as defined by the top end surface 13C thereof, while still allowing the gasket 11 to deform locally in a direction that is substantially centripetal relative to the axis of symmetry A of the. cooking vessel -1 , under the effect of the pressure acting through one or more gaps formed outside the contacting sector(s) so as to break sealing locally and establish a leak through which the pressure can escape between the reentrant rim 4, i.e. the end edge -5 and the lid 10. In the invention, the concept of pressure that is "excess" relates to the pressure inside the pressure cooker exceeding its normal operating pressure by more than 0.9 bars, for example. Advantageously, according to an important characteristic of the invention, the safety pressure-release device of the invention comprises means for causing the gasket 11 "to creep, said means being situated and implemented in or level with the groove 12 in a specific geometrical position that is substantially in the zone S corresponding to the major diameter D of the lid. As creep-inducing means, the groove 12 then includes a deformation 20 of its inner face 13A and a notch 21 or an orifice in its outer face 13B. In . addition, as mentioned above', the gasket 1 1 , the reentrant rim 4, and the lid 10 are shaped so that in the event of excess pressure, with the lid 10 being in abutment against the reentrant rim 4 via the periphery of its rolled edge 13, 13B, the gasket 11 creeps in centripetal manner locally because of the deformation 20 and under drive from the pressure acting through the notch 21 or orifice so as to break the.seal locally and allow steam to escape between the reentrant rim 4 and the lid 10. The fact of the gap for the gasket 11 being made in the zone S which corresponds to the major diameter of the lid 10 presents the advantage of reducing and limiting dimensional dispersion. It is along the major diameter D of the lid 10 that relative movement between the lid 10 and the vessel 1 is at its _minimum, thereby., in present circumstances, making it possible to benefit from maximum accuracy and safety concerning the positioning of the gasket 11 in the zone S. This control over the position of the gasket 11 relative to the vessel 1 and to the lid 10 makes it possible to define an elastic deformation zone for the gasket 11 thus .specifically enabling it to creep without destroying the appliance. Making a notch 21, preferably of circularly arcuate shape, enables a portion, of the side surface of the . gasket 11 to be uncovered, thus allowing the pressure P to act directly on the gasket 11 in substantially centripetal manner, as can be seen in Figure 6, thereby locally breaking the seal. Naturally, precautions are taken to facilitate centripetal movement or deformation of the gasket 11 by ensuring that enough space is available for it to move in the interface between the flanks TOB of the lid 10 and the end edge 5 of the reentrant rim 4. The deformation 20 is advantageously arranged to be symmetrical about the notch 21 and in radial alignment therewith. The deformation 20 can be 'obtained in particularly simple manner by stamping when forming the lid 10. Other shapes and other ways of obtaining local deformation of the lid can naturally be envisaged providing it is ensured that a local discontinuity is obtained in the general shape of the flank 10B situated in register or in radial alignment with the notch 21 so as to increase the space available for the gasket 11 to move in a centripetal direction. Advantageously, and as can be seen particularly well in the figures, the deformation 20 is formed by an indentation defining a substantially concave face. Advantageously, in order to improve control over the elastic deformation by creep of the gasket 11, the gasket has a weaker zone 30 of reduced section (Figure 5) for situating in register with the deformation 20 so as to encourage said gasket to creep locally. Advantageously, and as shown in particular in Figure 5, the zone of reduced section 30 is formed by recess of optionally regular shape, e.g. being substantially concave in shape and extending preferably from the inside face of the gasket 11. Advantageously, the recess is inclined so that its top portion at rest is further 'away from the inner face of the groove 12 than is its bottom portion. The recess 30 can be provided over the full height of the gasket,, or over a fraction only of its height going down from its top face. Making the creep-inducing means for the gasket 11 in the form of a deformation 20 and a notch 21 or orifice in the zone S serves to provide technical means that present a first level of safety against excess pressure, with 'creep of the gasket 1 1 taking place in a pressure range corresponding to approximately 1.4 bars to 3 bars. It should also be observed that the creep-inducing means are situated in register with and beneath the handle of the lid 26, thereby reducing the risks of steam squirting directly upwards from the pressure cooker and thus directly at the user. In the invention, it is also possible to envisage making an additional level of safety in the device of the invention for acting at a pressure higher than the pressure at which the gasket 11 creeps. This second level of safety is intended to mitigate any failure of the gasket to creep. Thus, in accordance with the invention, the device of the invention further comprises gasket-extrusion means in at least one zone different from the zone S corresponding to the major diameter of the lid 10, which gasket-extrusion means are made from or in the groove 12 and comprise a shape discontinuity 40' in its inner face 13A and a notch 41 or orifice in its outer face 1 3B (e.g. Figure 3). These extrusion means enable' the gasket 11 to be extruded out from the groove 12 under the effect of the pressure acting through the notch 41 or orifice in question, the gasket being extruded when the pressure reaches a value higher than the pressure at which the gasket ought to creep. Under such circumstances, extrusion of the gaskef 11 out from the groove 1 2 is accompanied by deformation of the reentrant rim 4 and of the pressure cooker as a whole, thus making it unusable thereafter. In a particularly advantageous version of the invention, as shown in Figure 4, the safety pressure-release device of the invention has a pair of extrusion means 40, 41 disposed in opposite locations in the groove 12 substantially at the ends of the minor diameter d of the lid 10. This provides two diametrically opposite extrusion zones that improve the safety of the appliance. . ' Advantageously, the shape discontinuity 40 is formed by an indentation defining a substantially concave face in the flank 10B of the lid 10 level with et gasket 11 when it is in position in the groove 12. Advantageously, the shape discontinuity 40 can be provided in the lid 10 level with the gasket and/or above the top of the gasket 11 when the gasket is in position in the groove 12. In general, care should be taken to ensure that the generator lines of the shape discontinuity 40 slope towards the axis of symmetry A of the appliance. In this way, all or part of the jets of steam that might escape during extrusion of the gasket are preferably directed towards a central zone and upwards from the pressure cooker, so as to avoid the jet of superheated steam squirting directly at the user. In a preferred variant of the invention, the position of the gasket 11 is indexed relative to the groove 12 by position-indexing means. Advantageously, the indexing means comprise at least one local increase in thickness 30A (Figure 5) extending substantially radially from the outer periphery of the gasket 11, said extra thickness being complementary in shape to the shape of the notch 41 so as to be engaged therein and rest thereon, thereby indexing the gasket. This feature makes it easier to position the gasket properly in the groove 12, and serves mainly to avoid the gasket being installed wrongly. The extra thickness 30A can be made and integrated in a peripheral lip' 30B for resting against the end 13C. The gasket 11 preferably has two localized extra thicknesses 30A that are diametrically opposite so as to be received in each of the notches 41. In a variant embodiment (Figure 8), the indexing means are associated with the creep-inducing means 20, 21,-the gasket 11 having one or more regions of extra thickness 31A situated locally on the inner periphery of the gasket 11 in register with the weaker zone 30, for example at opposite ends of the recess. In this variant, the extra thicknesses 31A are associated with concave notches 30C formed in the outer face of the gasket, for example where the gasket corresponds to the minor diameter d, for co-operating with complementary shapes of the lid 10. The gasket is extruded by means of the extrusion means 40, 41 when the pressure reaches a value substantially in the range 4.5 bars to 5 bars. The safety device of the invention operates as follows. In its normal operating position, the gasket 11 provides sealing for the manhole pressure cooker by preventing any pressure from passing from the inside of the- vessel 1 to the outside of the pressure cooker. In the.event of the pressure rising abnormally, and insofar as other safety devices belonging to the pressure cooker have failed to operate (e.g. a conventional safety valve), the lid 10 comes into contact with the inside face of the reentrant rim 4 via the top end 13C of its rolled edge 13B. This situation generally occurs when the excess pressure lies in the range approximately 1.4 bars to 1.7 bars. In this situation, the first safety level of the safety pressure-release device of the invention as formed by the creep-inducing means 20, 21 can come into operation. Thus, the pressure P can push back the gasket 11 centripetally in the zone S thus enabling the gasket to creep, i.e. to deform elastically and centripetally, thereby.locally breaking the seal and allowing steam to escape through the zone S situated beneath the handle 26 If for whatever reason, e.g. clogging or jamming of the gasket, poor positioning, etc., creep of the gasket is not obtained, the internal pressure will continue to rise until the extrusion means 40, 41 come into action. In this situation, the pressure causes the gasket to be extruded out from the groove 12 via the shape discontinuity 40 and the notches 41. Extrusion of the gasket 12 is accompanied by deformation of the lid and local breaking of sealing. The safety pressure-release device of the invention thus enables a manhole pressure cooker to be obtained that includes the means required for obtaining full control over locally breaking the seal provided by the gasket, with this being done at two different pressure levels. This provides an additional guarantee of safety for the.user. SUSCEPTIBILITY OF INDUSTRIAL APPLICATION The industrial application of the invention lies in manufacturing manhole pressure cookers and in manufacturing safety gaskets for fitting and using in such pressure cookers. We Claim: 1. Pressure cooker with manhole with an overpressure safety device, comprising a cooking chamber (1), with an oval opening bordered by a re-entrant rim (4) in which an oval lid (10) is able to be inserted, defining a small diameter (d) and a large diameter (D), in order to hermetically close the chamber (1) by means of a sealing joint (11) which is mounted in a peripheral groove (12) in the lid (10) forming a rolled edge (13) and defining an internal face (13A) and an external face (13B), the said joint thus coming into sealed abutment against the re-entrant rim (4), characterised in that, in the area (S) corresponding to the large diameter (D) of the lid (10), the groove (12) comprises creep means (20, 21) for the joint (11), and in that the joint (11), the re-entrant rim (4) and the lid (10) are formed so that, in the event of overpressure, the lid (10) being in a position of abutment against the re-entrant rim (4) through the periphery of the rolled edge (13), the joint (11) creeps locally through the creep means (20, 21) in a centripetal manner under the effect of the pressure acting through the creep means in order to break the seal locally and allow the steam to escape between the re-entrant rim (4) and the lid (10). 2. Pressure cooker as claimed in Claim 1, wherein the creep means are formed in the groove (12) by: -a deformation (20) in the internal face (13A), -a notch or orifice in its external face (13B). 3. Pressure cooker as claimed in Claim 2, wherein the deformation (20) is formed by a recessed part defining a concave face. 4. Pressure cooker as claimed in one of Claims 1 to 3, wherein the joint (11) comprises an area with a weakened cross-section (30) at the deformation (20) in order to assist the local creep of the joint. 5. Pressure cooker as claimed in Claim 4, wherein the area with a weakened cross-section (30) is formed by a recess provided as from the internal face of the joint (11). 6. Pressure cooker as claimed in one of Claims 1 to 5, wherein, at least in a different area from the large diameter (D) of the lid (10), the groove (12) comprises extrusion means (40, 41), so as to allow the extrusion of the joint out of the groove (12) under the effect of the pressure acting through the extrusion means (40, 41), the extrusion of the joint (11) occurring at a pressure value higher than the pressure value at which the joint creep takes place. 7. Pressure cooker as claimed in Claim 6, wherein the extrusion means of the groove (12) comprise: -a break in shape (40) in its internal face (13A), -a cut (41) or orifice in its external face. 8. Pressure cooker as claimed in Claim 6 or 7, wherein it comprises a pair of extrusion means (40,41) provided in opposition in the groove (12) in the area corresponding to the small diameter (d) of the lid. 9. Pressure cooker as claimed in Claim 7, wherein the break in shape (40) is formed by a recess part defining a concave face provided at the joint (11). 10. Pressure cooker as claimed in one of Claims 6 to 9, wherein the break in shape (40) is provided in the cover (10) at the joint (11) and/or above the top level of the joint (11) when the latter is in position in the groove (12). 11. Pressure cooker as claimed in one of the preceding claims, wherein the position of the joint (11) is located relative to the groove (12) by position locating means. 12. Pressure cooker as claimed in Claim 9, wherein the locating means comprise at least one local protrusion (30A) extending at the external periphery of the joint (11), with a shape conjugate to the cut (41), in order to fit in the latter. 13. Pressure cooker as claimed in Claim 11, wherein the locating means are associated with the creep means (20, 21). 14. Pressure cooker as claimed in Claim 13, wherein the locating means comprise one or more protrusions (31 A) situated locally at the internal periphery of the joint (11) at the weakened area (30). Dated this the 27* day of May, 2002 [JAYANTA PAL] Of Remfry &Sagar ATTORNEY FOR THE APPLICANT[S]

Documents:

in-pct-2002-00683-mum-cancelled pages(14-11-2005).pdf

in-pct-2002-00683-mum-claims(granted)-(14-11-2005).doc

in-pct-2002-00683-mum-claims(granted)-(14-11-2005).pdf

in-pct-2002-00683-mum-correspondence(3-8-2007).pdf

in-pct-2002-00683-mum-correspondence(ipo)-(18-4-2006).pdf

in-pct-2002-00683-mum-form 13(3-8-2007).pdf

in-pct-2002-00683-mum-form 19(25-10-2004).pdf

in-pct-2002-00683-mum-form 1a(14-11-2005).pdf

in-pct-2002-00683-mum-form 1a(27-5-2002).pdf

in-pct-2002-00683-mum-form 1a(3-8-2007).pdf

in-pct-2002-00683-mum-form 2(granted)-(14-11-2005).doc

in-pct-2002-00683-mum-form 2(granted)-(14-11-2005).pdf

in-pct-2002-00683-mum-form 3(14-11-2005).pdf

in-pct-2002-00683-mum-form 3(27-5-2002).pdf

in-pct-2002-00683-mum-form 5(27-5-2002).pdf

in-pct-2002-00683-mum-form-pct-ipea-409(14-11-2005).pdf

in-pct-2002-00683-mum-petition under rule 137(14-11-2005).pdf

in-pct-2002-00683-mum-power of authority(1-7-2002).pdf