GB2107969A - Water-boiling vessels - Google Patents

Abstract

An electrically heated water boiling vessel, such as an electric kettle 1, is provided with a whistle or like steam-powered audible-indication generating means, not shown, and also has an associated automatic cut- out for interrupting the electrical supply to the heating element when the water in the vessel boils, the cut- out switch including a temperature sensitive switch operating element which is arranged to be exposed to steam vented or ducted from the vessel interior when the vessel boils. The problem arises that the venting or ducting of steam to the switch operating element 6 reduces the steam pressure available for operating the whistle, and to overcome this a flap-valve 8 is provided in the vent or duct 3 leading to the switch operating element, the valve being normally closed and opening only when the steam pressure within the vessel has risen to such an extent as to obtain useful operation of the whistle. Alternatively a spring or gravity- loaded ball or poppet valve may be used. <IMAGE>

Description

SPECIFICATION Improvements relating to electrically heated water boiling vessels This invention concerns improvements relating to electrically heated water boiling vessels such as kettles, jugs, urns, etc. and is more particularly concerned with such vessels provided with a whistle or similar device adapted for proyiding an audible indication when the water in the vessel is boiling, the whistle or the like being operated by pressurized steam escaping from the body of the vessel.

Water boiling vessels are known in which an automatic cut-out switch is associated with the heating element of the vessel for interrupting the supply of electrical energy to the element when the water in the vessel boils, such vessels commonly including a temperature sensitive switch or switch operating element arranged to be exposed to the steam which is generated when the water in the vessel boils. In some arrangements, the steam generated when the water boils is simply vented through an opening in the vessel wall to impinge more or less directly upon the temperature sensitive element, whereas in other arrangements the steam is conveyed to the temperature sensitive element by way-of a tube, pipe or duct.

In such water boiling vessels as have been provided with a whistle (or like steam powered audible indication generating means) and also with an automatic steam induced switch-off facility, conflicting steam pressure requirements have been encountered as regards operation of the whistle and of the automatic switch-off. The known forms of whistle, including plain type whistles and reed type whistles, require a fairly substantial volume of high pressure steam in order that a usefully appreciable audible indication be generated, whereas automatic switch-off controls commonly utilizing a bimetallic element or a memory metal element for example are responsive within a few second of initiation of boiling when the steam pressure is grossly insufficient to operate the whistle.The vessel thus is switchedoff automatically long before a sufficient head of steam is generated to operate the whistle to an appreciable extent.

To achieve a steam-sensing, automatic switchoff water boiling vessel provided with a whistle or the like capable of making an audible sound when the water boils, recourse has been had in the past both to steam sensing controls having much higher operating temperatures and/or to restriction of the steam access area to the control via a restricted size tube, pipe or duct.Various disadvantages attach to both of these alternatives; the former requires non-standard controls which are disadvantageous from a manufacturing and from a distribution or supply viewpoint, particularly in view of the potentially hazardous risk of the wrong control being fitted to an appliance by virtue of the supply of the wrong control units to an installer, and the latter, namely restriction of steam access to the control, increases the likelihood of operation failure of the automatic switch-off facility on account of the access duct becoming blocked, for example by a water droplet.

The present invention resides in the concept of providing a valve in the path of access of steam from the vessel interior to the temperaturesensitive switch or switch operating element, the valve being normally closed but being openable by steam pressure to permit steam to access the control only when the steam pressure within the vessel has risen to such an extent as to obtain useful operation of the whistle.

The steam valve can take any convenient form and could for example comprise a spring or gravity loaded ball or poppet type valve, but preferably comprises a flap valve which advantageously cooperates with an inclined seating so as to be biassed by its own weight towards a closed position. A bottom hinged flap valve is preferred on account of the fact that, in combination with an inclined seating and biassing of the flap into its closed condition under its own weight, the force required to open the valve reduces as the valve approaches a vertical orientation.

The valve can be provided in a duct connecting the vessel interior with the temperature sensitive control or, where the arrangement of the control permits, can simply be provided associated with an opening in the vessel wall to control the venting of steam to access the control. In vessels where a steam pipe is provided to convey steam from the vessel interior to the control, the valve could even be incorporated as a unit adapted to be fitted to the end of the steam pipe.

The invention, together with features and advantages thereof, will be well appreciated from consideration of the foregoing and of the following description of an exemplary embodiment which is illustrated in the accompanying drawings showing a fragmentary view of an electrically heated kettle.

Referring to the drawing, the kettle 1 has a steam vent 2 formed through its wall, and on the outside of the kettle body there is provided a duct 3, defined by a channel-shaped lower moulding 4 and a cover moulding 5, for directing steam venting from the kettle interior towards a steamsensitive control unit 6 having a steam inlet 7. The unit 6 may be any suitable control unit incorporating a temperature sensitive switch or switch actuating element, preferably of a snapacting variety, operating to disconnect the kettle element from the electrical supply when steam from the kettle interior accesses the unit.

As shown, a flap valve 8 is pivotally mounted on a pair of pins 9 formed in the lower moulding 4, the pins being received in oversize holes formed in the flap valve and the arrangement being such that with the kettle placed on the level, the flap valve cannot pivot beyond vertical so that it is always subject to a gravitational restoring bias.

The valve 8 cooperates with a raised annular seat 10 formed around an opening in the moulding 4 which closely overlies the vent 2 in the kettle wall, the seat 10 being in a generally inclined plane.

In operation, steam is prevented by the valve from passing to the control unit until the steam pressure within the kettle is high enough to lift the valve from its seating by which time the kettle whistle (not shown) is operating. The pressure which builds up within the kettle is determined by the size of the whistle aperture, any other vents (e.g. gaps around the lid if fitted), the element wattage and the water volume. The force required to open the valve depends on its weight and attitude as well as such things as the surface tension of the water film between the valve and seat, and is produced by the product of the internal kettle pressure and the exposed area of the valve. The effect of suface tension can be varied, by altering the radial thickness of the annular seat, with, from the test results so far obtained, a narrow seat appearing to give the greatest consistency of operation.

As will be appreciated by those skilled in the art, the present invention enables the provision of an automatic, steam-sensing switch-off kettle having an audible boiling indicator which uses standard temperature sensitive controls without recourse to small area steam ducts and thus avoids, or at least greatly reduces, the problems mentioned herein which previously have been encountered.

Claims (8)

1. An electrically-heated water-boiling vessel of a type including a whistle or other steam-powered audible indication generating means adapted to provide an audible indication when water heated in the vessel boils and generates sufficient steam pressure to operate the indication generating means, and an automatic cut-out switch associated with the heating element of the vessel for interrupting or reducing the supply of power to the said element when water heated in the vessel boils, the said switch comprising a temperaturesensitive element arranged to be exposed to steam vented or ducted from the vessel and valve means being provided in the path of access of steam generated in the vessel to the temperaturesensitive element, the valve means being normally closed but being openable by steam pressure to permit steam to access the temperature-sensitive element only when the steam pressure within the vessel has risen to such an extent as to obtain useful operation of the audible indication generating means.

2. A vessel according to claim 1 wherein said valve means comprises a spring or gravity loaded ball or poppet type valve.

3. A vessel according to claim 1 wherein said valve means comprises a flap valve.

4. A vessel according to claim 3 wherein said flap valve is arranged so as to cooperate with an inclined seating so as to be biassed by its own weight towards a closed position.

5. A vessel according to claim 4 wherein said flap valve is bottom hinged whereby the force required to open the valve reduces as the valve approaches a vertical orientation.

6. A vessel according to any of the preceding claims wherein the valve means is associated with an opening in the vessel wall to determine the venting of steam through said opening to access the temperature-sensitive element.

7. A vessel according to any of claims 1 to 5 wherein a steam pipe is provided for conveying steam from the vessel interior to the temperaturesensitive element, the said steam pipe having an end within the vessel above the normal level of liquid within the vessel and the valve means being associated with said end to determine the access of steam to and through the steam pipe.

8. An electrically-heated water-boiling vessel substantially as herein described with reference to the accompanying drawing.