GB2208131A

GB2208131A - Safety venting device

Info

Publication number: GB2208131A
Application number: GB8715616A
Authority: GB
Inventors: Geoffrey Robinson
Original assignee: Prestige Group UK PLC
Current assignee: Prestige Group UK PLC
Priority date: 1987-07-02
Filing date: 1987-07-02
Publication date: 1989-03-01
Anticipated expiration: 2007-07-02
Also published as: GB2208131B; GB8715616D0

Abstract

In a safety venting arrangement for pressure cookers a gasket 5 seals the lid 3 to the base 1 of a cooker and also covers an opening 12 in the lid or base that extends to a region close to the inward edge of the gasket. A slot 10 through which the gasket can bulge when the pressure reaches a predetermined safety limit is provided so that when the safety limit is reached the gasket is pushed outwardly through the slot and this uncovers the opening to vent the cooker. In the event of a continued rise in pressure the gasket deforms further and the seal between the lid and base is also broken to provide futher venting. <IMAGE>

Description

SAFETY DEVICE This invention relates to safety venting devices.

Various types of safety devices have been incorporated on pressure cookers that vent the cooker when a predetermined safe pressure is exceeded, in some instances a plurality of devices is included responsive to different pressure levels.

One type of safety pressure relief device is a gasket blowout slot where excess pressure in the cooker deforms the sealing gasket and pushes part of it out of a slot. This mechanism relies upon radial deformation of the gasket and so the slot is provided in a down turned edge portion on the lid which is the radial constraint to the gasket. The result of deforming the gasket out of the slot is that at that position the gasket is removed from its sealing engagement between the base and the lid of the cooker and so venting occurs where the seal is broken.

Gasket blow out devices are reliable but when safety venting occurs it makes a considerable noise due to the fact that a pressure significantly above normal operating pressure is required to deform the gasket sufficiently to break the seal, and when the seal is broken that high pressure is vented to atmosphere very rapidly.

According to the invention there is provided a pressure relief mechanism for a pressure cooker having a lid and a base, the mechanism comprising a gasket for sealing the lid tolbase, a relieved portion radially outwardly of the gasket and an opening covered by the gasket and extending proximate an inward portion of the gasket so that at a particular pressure the gasket is deformed into said relieved portion and this deformation causes a portion of the gasket to expose the opening to relieve pressure.

In another aspect the invention provides a pressure relief mechanism for a pressure cooker having a lid and a base in which a deformable gasket seals the pressure cooker lid to the base and a slot is provided radially outwardly of the gasket through which the gasket is deformed at a particular pressure to an extent such that the gasket seal is broken and safety venting occurs, and in which an opening is provided proximate an inward portion of the gasket such that deformation of the gasket through the slot vents the cooker via the opening prior to the said safety venting.

The invention is now described by way of example with reference to the accompanying drawings in which: Figure 1 illustrates the prior art; Figure 2 shows an embodiment of the invention, and Figure 3 is a plan view of a portion of a base of a cooker illustrating alternative embodiments of the invention.

Referring to Figure 1, a typical pressure cooker base and lid sealing arrangment is shown in the closed position. The cooker comprises a base 1 having an outwardly turned flange 2 and a lid 3 with a downwardly turned edge portion 4. The lid 3 fits over the flange 2 on the base and is supported on the flange with a resilient sealing gasket 5, made for example of silicone rubber or nitrile rubber, trapped between the lid and flange. In order to retain the lid on the base when the cooker is pressurised a mechanical locking arrangement needs to be provided, this could be clamps or any other suitable mechanism but in the drawing interleaving bayonet locking lugs 6 are shown. It should be noted that the lugs are in dotted outline as they are not in the plane of the section.

The locking lugs 6 are radially inward projections from the edge portion 4 of the lid and radially outward projections on the flange 2 of the base, the edge portion 4 and flange 2 each having a plurality of circumferentially spaced lugs with the spaces between adjacent lugs on the base flange being sufficiently large to enable the lugs on the lid flange to pass between them, and vice versa. Once the lid is in position the lid lugs are at a lower level than the base lugs and rotation of the lid to align the lid lugs with the base lugs provides the necessary clamping. The lugs may have cammed profiles and other refinements for safety and secure clamping but these are not fundamental to the present invention and so are not described further.

In the closed position, as shown, there is a gap 8 between the lid edge portion 4 and base flange 2 at locations between lugs which would present a passage for gas from the cooker; the gasket 5 bridges the gap 8 and as pressure builds up it is urged in the directions of arrows 9 against the base and lid to provide a gas seal. A slot 10 is provided in the lid edge portion 4 intermediate the lug locations and, as pressure in the cooker builds up the gasket continues to be urged radially outwardly until eventually under continued increase of pressure the gasket bulges through the slot 10 as shown in Figure lb. This breaks the seal between the base and lid and the cooker is vented by gas escaping through the gap 8 as shown by arrow 11.With other locking structures the exact escape route for gas may be different but in general it will be downwardly due to the general arrangement of the edge poartion of the lid extending over the sides of the base.

Referring now to Figure 2, an embodiment of the invention is illustrated on a pressure cooker of the same type as described with reference to Figure 1. A slot 10 is also provided and the gasket deforming operation explained above operates similarly in sealing and then, at a higher pressure being forced to bulge through the slot 10. However in the invention a second opening 12 is provided on the upper surface of the lid. The opening 12 is in the area that under normal operating pressure would be covered, and therefore sealed, by the upper lip 13 of the gasket 5. When the pressure rises sufficiently to urge the gasket to bulge out through the slot 10 the gasket will adopt the position shown in Figure 2, the gasket bulge causing lip 13 to expose the second opening 12 so that gas is vented upwardly through that opening.

It should be noted th-at the second opening is vented before the lower lip 14 reaches the edge of the base flange 2. This can be achieved either by having the inner edge of the opening 12 more radially inward than the edge of the base flange (as shown in Figure 2) or other potential vent and/or by having an asymmetric gasket in which the upper and lower lips 13,14 are of different lengths: if the edges of the opening 12 and gap 8 are at similar radial distances the lower lip 14 should be longer so that the upper opening is exposed first.

The pressure required to deform the gasket out the slot 10 sufficiently to cause venting is determined by gasket deformability, size of slot 10, and relative positions of lip 13 and the inner edge of the second opening, but relief via the opening 12 requires less deformation (less bulging) of the gasket than is necessary to provide safety venting of the cooker as described in relation to Figure 1. The relief through the second opening 12 is progressive and increases with increasing pressure since greater pressure causes a greater movement of the gasket through the slot 10 to expose a greater extent of the opening 12. This feature may be emphasised or adjusted by varying the shape of the opening 12, although it is generally envisaged that a circular 5 opening will be satisfactory. A vented cover (not shown) may be provided for the opening, this cover may act as a baffle or deflector for the vented fluid. A convenient arrangement is for the cover to be incorporated in a part of a handle assembly that extends over the lid, and in this instance the portion covering the opening can be arranged to direct escaping gas away from the handle.

To some extent it might be considered that the Figure 1 arrangement exhibited progressive venting in that the gap 8 would be progressively more exposed with increasing pressure, but with the Figure 1 arrangement by the time safety venting takes place the gasket has undergone a more extensive deformation than that required to vent via the opening 12 of Figure 2, and also the gap 8 when exposed is much more extensive than the opening 12 and so the venting via gap 8 tends to be rapid and uncontrollable. In contrast the present invention is adapted to vent at a lower pressure, with less gasket deformation and is therefore potentially more consistent and vents in a quieter manner. It will be realised that once pressure is relieved the gasket can return to its sealing location and thus the arrangement provides a regulated relief that is self resetting.Due to the tendency of the upper lip to be mechanically retained in the opening 12 and deformed by the passage of escaping gas, the gasket does not reseat until the pressure is relieved to below normal operating pressure whereupon the gasket reseats within the lid edge portion 4 and reseals as described previously as the pressure rises back to operating pressure.

In many instances relief via opening 12 is all that is required and no further safety venting becomes necessary, for example if the cause of the excess pressure build up was a temporary blockage or if the user becomes aware of a more permanent cause. If the cause remains, the cycle of relief via the opening 12 is repeated. In the event that relief via opening 12 is not sufficient to prevent a continued rise in pressure within the cooker the gasket continues to deform and bulge further out of the slot 10 and then the seal between the base and lid is broken and further venting occurs in the known manner. Thus with the present invention safety venting is introduced at a lower level and the prior art venting mechanism remains as a back up.

A further advantage of the invention over the prior art arrangement is that it may function as a fail safe device for deteriorated gaskets. It is found that as they get old pressure cooker gaskets shrink and become less resilient which tends to increase the time taken for the gasket to seat properly into sealing engagement. This is irritating for the user and inefficient because it takes longer for the cooker to pressurise (and could result in over cooking). Thus in a preferred embodiment of the invention the second opening is positioned so that when gasket shrinkage occurs (the extent of which can be predicted) the lip will not extend over the opening 12. The cooker is therefore fail safe by virtue that it will not pressurise and the user is reminded to replace the gasket.A visual indication to the user that gasket shrinkage has occurred (other than by inspection of the gasket) is given by steam escaping via the opening 12 in the early stages of cooking, prior to or on commencement of pressurising, because venting through opening 12 at this stage of cooking would not occur with a good gasket. This indication is all the more visible because of the location of opening 12 and is more readily detected than leakage from under the lid as happens with the prior art.

A modification that is envisaged is for the slot 10 to be replaced by a recess. In this instance the recess provides a relieved portion, as does a slot, into which the gasket can be deformed to cause an inner part of the gasket to reveal an opening. It is also possible for the opening to be made on the base of the cooker rather than the lid or for the opening to be constituted by a slot or notch that extends inwardly from the edge of the lid or base, for example as shown in Figure 3 with a notch 15 in the base flange 2 extending inwardly to the vicinity of the location of the inner edge of the lower lip of the gasket. Figure 3 also illustrates an alternative opening, a hole 16 in the flange and lug.

Claims

1. A pressure relief mechanism for a pressure cooker having a lid and a base, the mechanism comprising a gasket

for sealing the lid tobase, a relieved portion radially outwardly of the gasket and an opening covered by the gasket and extending proximate an inward portion of the gasket so that at a particular pressure the gasket is deformed into said relieved portion and this deformation causes a portion of the gasket to expose the opening to relieve pressure.

2. A pressure relief mechanism for a pressure cooker having a lid and a base in which a deformable gasket seals the pressure cooker lid to the base and a slot is provided radially outwardly of the gasket through which the gasket is deformed at a particular pressure to an extent such that the gasket seal is broken and safety venting occurs, and in which an opening is provided proximate an inward portion of the gasket such that deformation of the gasket through the slot vents the cooker via the opening prior to the said safety venting.

3. A pressure relief mechanism according to any preceding claim in which the opening is in the lid so that any fluid escaping from the cooker is vented upwardly.

4. A pressure cooker relief mechanism according to any preceding claim in which the opening is an open ended slot or notch that extends inwardly from the edge of the lid or base.

5. A pressure relief mechanism according to any preceding claim in which the opening is shaped to present a radially varied cross section.

6. A pressure relief mechanism according to any preceding claim in which the opening is located such that shrinkage of the gasket prevents the cooker from sealing.

7. A pressure relief mechanism according to any preceding claim in which the opening is provided with a cover.

8. A pressurecooker assembly according to any preceding claim in which the gasket is asymmetric.

9. A pressure cooker relief mechanism substantially as hereinbefore described with reference to and as illustrated in Figure 2 or Figure 3 of the drawings.

9. A pressure relief mechanism according to any preceding claim in which the opening is covered by a portion of a handle assembly.