GB2123528A

GB2123528A - Pressure relief plugs

Info

Publication number: GB2123528A
Application number: GB08317844A
Authority: GB
Inventors: Geoffrey Robinson
Original assignee: Prestige Group UK PLC
Current assignee: Prestige Group UK PLC
Priority date: 1982-07-16
Filing date: 1983-06-30
Publication date: 1984-02-01
Also published as: GB8317844D0; GB2123528B

Abstract

A pressure relief plug for a pressure vessel includes a resilient member 5 which can be mounted in an aperture 9 in the vessel cover or top wall. A closure member incorporating a valve portion 18 is movable axially through an aperture 12 in resilient member 5 to close the aperture at a predetermined pressure (Fig. 6). A further rise in pressure will force the valve portion 18 up through the aperture 12 to vent the vessel. The resilient member 5 is forcibly expelled from the cover or top wall if the pressure within the vessel reaches an unacceptable level but the plug is retained attached to the cover or top wall by means of a retaining member 16 within the vessel (Fig. 8). The retaining member 16 has a length greater than a diameter of the aperture 9 in the vessel cover or top wall. The valve portion 18 is of fusible material which melts in the event of excessive temperature, thus venting the vessel. <IMAGE>

Description

SPECIFICATION Pressure relief plugs The invention relates to pressure relief plugs for pressure vessels, particularly pressure cookers.

Pressure vessels, such as pressure cookers of the domestic type, generally incorporate a pressure relief plug as a safety device which is designed to automatically vent the vessel should the pressure within the vessel exceed a predetermined pressure. Some such pressure relief plugs are also designed to vent the vessel when an undue rise in temperature occurs whether or not it is accompanied by an undue rise in pressure. A pressure relief plug of this type is described in U.K. Patent Specification No.

662889. As explained in the afore-mentioned specification if the proper functioning of the prior art pressure relief plug is prevented, e.g. by obstruction of the valve mechanism, the whole plug is forcibly expelled from the pressure vessel should the pressure within the vessel attain an unacceptable level, generally higher than the predetermined pressure.

According to the present invention there is provided a pressure relief plug for a pressure vessel comprising a resilient member adapted to be mounted in an aperture in the cover or top wall of the vessel, a closure member extending through an aperture in the resilient member and movable axially of said aperture, said closure member being movable under a first predetermined pressure within the vessel to cause a valve portion of the closure member to seal the aperture in the resilient member, the resilient member being adapted to be forced out of the aperture in the cover or top wall under excess pressure within the vessel and the closure member being provided with upper and lower retaining members at opposite ends of the closure member for retaining the closure member connected with the resilient member, the lower retaining member having at least a portion of greater length than a diameter of the aperture in the cover or top wall such that the said retaining member is adapted to be retained within the vessel should the resilient member be forced out of the aperture in the cover or top wall.

It will be seen that the pressure relief plug of the present invention has the advantage over that of the above mentioned specification in that, although the plug may be forcibly expelled from the vessel should the pressure within the vessel reach an unacceptable level, the plug is designed to remain attached to the vessel by means of the lower retaining member so avoiding loss of the plug or possible danger resulting from the plug being expelled from the vessel at, for example, high speeds.

Preferably at least part of the closure member of the plug is fusible at excess temperature so that the plug of the invention retains the capability of venting the vessel at excess temperature (whether or not accompanied by excess pressure).

Preferably part only of the closure member is fusible so that it is possible for the remainder of the closure member, particularly the retaining members, to be formed out of non-fusible material to give the member extra strength and also to prevent the ejection of the remainder of the closure even at excess temperature. For example the valve portion, or part thereof, may be formed of fusible material (such as a tin/bismuth alloy) while the two retaining members and the connection between them may be formed of, for example, aluminium. If all the closure member is non-fusible a separate fusible plug may be incorporated in the cover or top wall of the pressure vessel, if desired.

The pressure plug of the present invention is preferably constructed so that at a second predetermined pressure which is above the first predetermined pressure but below the excess pressure (at which the resilient member is forced out of the aperture in the vessel the valve portion of the closure member is forced through the aperture in the closure member without being entirely detached therefrom to permit release of the pressure from the vessel through the aperture in the closure member.The valve portion of the closure member may be arranged so that at pressures below the first predetermined pressure the plug acts as an air bleed i.e. when the pressure vessel, particularly a pressure cooker, is heated excess air will be driven out of the vessel through the open valve portion but as soon as the vessel reaches a predetermined pressure, which is lower than the normal operating pressure, the valve portion closes the aperture in the closure member so that the vessel can be brought to cooking pressure. After completion of a normal cooking cycle when the pressure within the vessel again falls below the above mentioned predetermined pressure the valve portion re-opens the aperture in the closure member.

The lower retaining member of the closure member may be constructed so that it is substantially self-centering in the centre of the apertures in the resilient member and/or the vessel. For example it may comprise a bar-like portion substantially perpendicular to the axis of the closure member, said bar-like portion being of greater length than a diameter of the aperture in the cover or top wall and having one or more supports extending from the bar-like portion (preferably from near an end or ends thereof) towards the axis of the closure member at a position intermediate between the two retaining members.

The upper portion of the closure member, e.g.

the upper retaining member, and/or the upper surface of the resilient member may carry indicating means for indicating the position of the upper retaining member relative to the upper surface of the resilient member. Such indicating means can be used as an indication of the pressure conditions within the vessel. In a preferred embodiment, the upper surface of the resilient member is provided with an upstanding flange portion such that at least part of the closure member, for example some or all of the upper retaining member, is adapted to lie below the level of the upper surface of the flange portion when the vessel is at one pressure and above the level of the upper surface of the flange portion when the vessel is at a higher pressure.

The invention further provides a pressure vessel including a pressure relief plug according to the invention.

An embodiment of the pressure relief plug for use with a pressure vessel will now be described by way of example and with reference to the accompanying drawings in which Figure 1 is a fragmentary vertical section view of a pressure cooker having a cover provided with a pressure relief plug Figure 2 is an enlarged fragmentary vertical sectional view of the plug and adjacent portions of the cover showing the relative positions of parts of the plug when the pressure within the cooker is atmospheric or less Figure 3 is a bottom plan view of the plug as viewed in the direction of arrow Ill of Figure 2 Figure 4 is a top plan view of the plug as viewed in the direction of arrow IV of Figure 2 Figure 5 is a sectional view corresponding to Figure 2 but showing the relative positions of the parts when the pressure cooker is being vented Figure 6 is a sectional view corresponding to Figure 2 but showing the relative positions of the parts at the completion of the venting operation and when the pressure within the cooker is at normal cooking pressure Figure 7 is a sectional view corresponding to Figure 2 but showing the relative positions of the parts when excess pressure within the cooker has caused the cooker to be vented Figure 8 is a sectional view corresponding to Figure 2 but showing the relative positions of the parts when excess pressure within the cooker has caused the plug to be ejected from the cover Figure 9 is a sectional view corresponding to Figure 2 but showing the parts when excess heat within the cooker has caused melting of a fusible part of the plug.

As shown in Figure 1, a pressure cooker comprises a body portion 1 and a cover portion 2.

Mounted upon the cover portion 2 is conventional weight valve 3 and a pressure relief plug 4 according to the invention.

As more clearly shown in Figures 2 to 4, the pressure relief plug 4 comprises a resilient member 5 which may be made, for example, of rubber or the like and a closure member 6. The resilient member 5 is essentially disc-shaped but has an upstanding flange 7 on its upper surface.

The member 5 has a peripheral groove 8 to accommodate the edge of the aperture 9 in the cover portion 2 of pressure cooker. The lower surface 10 of the resilient member, which is intended to be positioned within the pressure cooker is of slightly greater diameter than the upper surface 11 which is intended to be positioned outside the pressure cooker. The resilient member has a stepped aperture 12 therethrough to accommodate the closure member 6.

The closure member 6 has a bar like portion 13 of smaller diameter than the smallest diameter of the aperture 1 2 and which in the normal position on the cooker is intended to be substantially vertical. The lower end of the bar like portion 13 carries two inclined portions 14, 1 5 which support a lower retaining member 16, substantially perpendicular to the bar like portion 1 3. The length of the lower retaining member 16 is somewhat greater than the diameter of the aperture 9 in the cover. On the upper end of the bar like portion 13 is an upper retaining member 17 of greater diameter than the smallest diameter of the aperture 12. The bar like portion 13, the inclined portions 14, 1 5 and the lower and upper retaining members 16, 17 may be formed from, for example, aluminium.The upper retaining member 1 7 may be provided with indications, such as a plastic coloured cap, to aid in indicating its position relative to the upper surface 11.

Situated on the bar like portion 13 intermediate its ends is a collar 18 which comprises a valve portion adapted to close the aperture 1 2 as described hereinbelow. The collar 1 8 may be made of fusible material, e.g. a tin/bismuth alloy, or may be made of non-fusible material such as that used for the bar like portion 13.

The relief plug 4 occupies the position shown in Figure 2 when the pressure within the cooker is atmospheric (or below). The valve portion 1 8 is clear of the aperture 12 and the upper retaining member 17 lies within the flange 7 such that it is largely hidden from the operator's view.

When the pressure cooker is heated the pressure relief plug initially acts as an air bleed and excess air is driven out through the aperture 12. The plug takes up firstly the position shown in Figure 5 and then that shown in Figure 6. In the latter position the upper retaining member 1 7 is visible to the operator, indicating that the pressure cooker is under pressure. In the normal operating position as shown in Figure 6 the valve portion 1 8 acts to seal the aperture 12 extending through the resilient member 15. At the end of the normal cooking cycle the pressure within the cooker is reduced and the plug resumes the position shown in Figure 2.

If during the cooking cycle excess pressure is built up within the cooker, the excess pressure acts on the closure member 6 and forces it axially out of the aperture 12 sufficiently to cause the valve portion 18 to pass completely through the aperture 1 2 by distorting the portions of the resilient member 5 surrounding the aperture such that the plug adopts the position shown in Figure 7. In this position the aperture 1 2 is open, so relieving the pressure within the cooker. The closure member 6 is retained in the resilient member 5 by the inclined portions 14. 1 5 of the lower retaining member. The plug may be re-set, e.g. after investigating and correcting the cause of the excess pressure, by pressing on the upper retaining member 1 7 to force the valve portion 1 8 back down through the aperture 1 2.

The normal means of relieving excessive pressure described immediately above with reference to Figure 7 may sometimes be interfered with if, for example, the aperture 1 2 becomes obstructed with particles of food or other matter.

In this instance excessive pressure (normally somewhat higher than that at which the valve member 1 8 is forced upwardly through aperture 12) causes the resilient member 5 to be distorted so that it is forcibly ejected from the aperture 9 in the cover 2 thereby relieving the pressure as shown in Figure 8. However, the plug 4 remains attached to the cover 2 since the lower retaining member 16 cannot pass through the aperture 9 in the cover. The inclined portions 14 and 1 5 aid in centering the closure member 6 during its passage through the aperture 9.

The embodiment in which collar 18 is made of fusible material is of particular value when there is an undue rise in temperature of the cooker, for example if the contents boil dry, whether or not this is accompanied by an excessive rise in pressure. In this instance the fusible collar of the valve portion 1 8 will melt thereby immediately venting the cooker through the aperture 12, as illustrated in Figure 9. It will be appreciated that the fusible collar should be formed of a suitable metal or alloy that does not melt at normal cooking temperatures but will melt when excess temperature occurs.

Claims

1. A pressure relief plug for a pressure vessel comprising a resilient member adapted to be mounted in an aperture in the cover or top wall of the vessel, a closure member extending through an aperture in the resilient member and movable axially of said aperture, said closure member being movable under a first predetermined pressure within the vessel to cause a valve portion of the closure member to seal the aperture in the resilient member, the resilient member being adapted to be forced out of the aperture in the cover or top wall under excess pressure within the vessel and the closure member being provided with upper and lower retaining members at opposite ends of the closure member for retaining the closure member connected with the resilient member, the lower retaining member having at least a portion of greater length than a diameter of the aperture in the cover or top wall such that the said retaining member is adapted to be retained within the vessel should the resilient member be forced out of the aperture in the cover or top wall.

2. A pressure relief plug as claimed in Claim 1 wherein at least part of the closure member if fusible at excess temperature so as to vent the vessel.

3. A pressure relief plug as claimed in Claim 2 wherein part only of the closure member is fusible.

4. A pressure relief plug as claimed in any one of Claims 1 to 3 constructed so that at a second predetermined pressure which is above the first predetermined pressure but below the excess pressure, the valve portion of the closure member is adapted to be forced through the aperture in the closure member without being entirely detached therefrom so as to permit release of the pressure from the vessel through the aperture in the closure member.

5. A pressure relief valve as claimed in any one of Claims 1 to 4 in which the lower retaining member comprises a bar-like portion substantially perpendicular to the axis of the closure member, said bar-like portion being of greater length than a diameter of the aperture in the cover or top wall and having one or more supports extending from the bar-like portion towards the axis of the closure member at a position intermediate between the two retaining members.

6. A pressure relief plug as claimed in any one of Claims 1 to 5 wherein the upper portion of the closure member carries indicating means for indicating the position of the upper retaining member relative to the upper surface of the resilient member.

7. A pressure relief plug as claimed in any one of Claims 1 to 6 wherein the upper surface of the resilient member is provided with an upstanding flange portion such that at least part of the closure member is adapted to lie below the upper surface of the flange portion when the vessel is at one pressure and above the level of the upper surface of the flange portion when the vessel is at a higher pressure.

8. A pressure relief plug substantially as hereinbefore described with reference to the accompanying drawings.

9. A pressure vessel incorporating a pressure relief plug as claimed in any one of Claims 1 to 8.