WO2011077136A1

WO2011077136A1 - Liquid heating apparatus

Info

Publication number: WO2011077136A1
Application number: PCT/GB2010/052167
Authority: WO
Inventors: Jonathan Michael White; Vincent Joseph Garvey; Norman Eric Nichol
Original assignee: Strix Limited
Priority date: 2009-12-21
Filing date: 2010-12-20
Publication date: 2011-06-30
Also published as: GB0922197D0

Abstract

A liquid heating apparatus (1) for heating a variable volume of liquid comprises a heating chamber (2), an inlet funnel (18) for directing liquid into the heating chamber (2) through an aperture (24) therein, and valve means (40) associated with the aperture (24). The valve means (40) has at least a semi-closed configuration from which it seals the aperture (24) in response to an increase in pressure in the heating chamber (2) during heating, but from which it can allow liquid to pass through the aperture (2) from the inlet funnel (18) during filling.

Description

Liquid Heating Apparatus

This invention relates to a liquid heating apparatus for heating/boiling liquids such as water.

There is a common need almost all over the world to heat water in order to make beverages. In the UK and other parts of Europe, it is common for most households to own a kettle which is used to boil water for making occasional beverages. In larger establishments and also in other parts of the world, it is more common to keep a body of water hot or boiling for a prolonged period of time - possibly all day - in order to be able to make such beverages "on demand", i.e. without having to wait for the water to heat up from room temperature. An example of this would be a traditional electric urn or, more commonly in Asia, a so-called airpot.

Both of these arrangements have their disadvantages. In the case of the kettle, the time taken for the water to heat from cold (i.e. the temperature from which it is drawn from the tap) is seen as inconvenient to users, even those using very high power kettles (of the order of 3 kilowatts). This is particularly so given the difficulty in estimating the volume of water required when the kettle is being filled and the attendant tendency to boil more water than is needed which of course increases the time taken for it to boil. On the other hand, if water is kept for a prolonged period of time either at or just below boiling, a significant amount of energy will be required to counter the unavoidable heat loss.

Recently, devices attempting to bridge this gap have been commercialised. These are said to be able to deliver a cupful of hot water from a reservoir of cold water within a matter of seconds. However, these devices are typically based on a tubular flow heater and the applicant has appreciated some significant drawbacks to this arrangement. Firstly, as is typical of tubular flow heaters, heating must be ceased before the water in the tube reaches boiling point in order to avoid the danger of the heater overheating through hot spots created by pockets of water vapour and/or the pressure inside the tube building up too high. Another drawback is that although the heater heats up relatively quickly, there is inevitably an initial volume of water which passes through the heater which is not heated to the target temperature. This mixes with the water produced later, itself still not at boiling point, to reduce the average temperature of the water. The combination of these two factors means that in practice the water provided by such devices is at well below boiling point by the time it is dispensed making it unsuitable for example for making tea and thereby limiting its consumer appeal.

When viewed from a first aspect the invention provides a liquid heating apparatus for heating a variable volume of liquid comprising:

a heating chamber;

an inlet funnel for directing liquid into the heating chamber through an aperture therein; and

valve means associated with the aperture and having at least a semi-closed configuration from which it seals the aperture in response to an increase in pressure in the heating chamber during heating, but from which it can allow liquid to pass through the aperture from the inlet funnel during filling.

Thus it will be appreciated by those skilled in the art that in accordance with the present invention a user can fill the heating chamber with a desired, variable volume of liquid which can then be heated and dispensed from the chamber under pressure generated during heating. The amount heated is determined (typically within limits) by the amount of liquid introduced into the inlet funnel. This means that the apparatus is highly flexible since it is not necessary for a user to think about what volume of heated liquid he or she requires and moreover different volumes can be accommodated in subsequent operations with no adjustments being necessary. This is also beneficial in reducing the use of energy since only the correct amount is heated each time. For example a user can fill the heating chamber with a cupful of water so that exactly the right amount of water is boiled and can then be subsequently dispensed back into the cup e.g. for preparing a hot drink in the cup.

Since the valve means seals the aperture during heating it can assist the desired build-up of pressure but the sealed valve also prevents escape of steam / heated liquid through the aperture into the inlet funnel and it prevents the unwanted leaking of any liquid remaining in the inlet funnel during heating. The valve means could be arranged such that it is resiliency biased into the semi- closed configuration. Means could be provided to overcome or reduce the resilient bias when the chamber was being filled or, more simplistically, the bias force could be chosen such that the pressure of liquid in the inlet funnel is able to overcome it automatically. In preferred embodiments however the valve means comprises a buoyant valve member arranged such that a predetermined minimum level of liquid in the heating chamber brings the valve means into the semi-closed configuration. Again external means could displace the valve member to permit filling but preferably the buoyancy of the valve member is chosen such that the pressure of liquid in the inlet funnel is able to displace it sufficiently to permit the heating chamber to be filled beyond the predetermined minimum level.

In one set of such embodiments the buoyant valve member comprises a flap valve configured so as to be held shut when the heating chamber is filled to the predetermined minimum level. Conveniently this could comprise a downwardly open cup at the distal end of the valve, in which air is trapped in use by the liquid beneath, thus causing the flap to be pressed against its valve seat when the heating chamber is filled to the minimum level but which allows the flap to be displaced while liquid is being added.

However in a preferred set of embodiments, a freely floating valve member is employed, which may be more robust than a flap valve. Advantageously, such a valve member is received in a housing which permits liquid flow through it but retains the valve member, the valve member having an upper position

corresponding to the semi-closed configuration in which it is against a valve seat and a lower position where it is retained in the lower part of the housing.

The valve member might take any convenient form. For example it could comprise a ball. Alternatively it could be pill, discus or squat-cylindrical in shape. In a preferred set of embodiments the valve member is downwardly tapering, e.g. frusto- conical. This has been found to minimise the chance of the valve member sticking during use.

In all embodiments the valve means is preferably configured such that increasing pressure in the heating chamber, i.e. during heating, tends to force the valve closed. This will of course be the case with the flap valve and valve members discussed above. Preferably the valve member is pressed against a sealing surface, e.g. a resilient collar, by internal pressure in the heating chamber during heating.

Preferably the sealing surface is located in the lower half of the heating chamber and defines the predetermined minimum fill level. In other words it is preferred that the predetermined minimum fill volume is less than half the total volume of the heating chamber - e.g. less than a third, e.g. less than a quarter. Clearly the smaller the ratio of the maximum to the minimum volume, the greater the range of fill volumes that can be accommodated. The maximum volume is typically determined by the physical capacity of the heating chamber.

The volume of the heating chamber is advantageously suitable to heat a wide range of volumes of liquid, e.g. for filling small cups and large mugs of water. Preferably the maximum volume of water the heating chamber can heat is at least 400 ml, preferably at least 500 ml. Preferably the predetermined minimum volume of water is less than 250 ml, preferably less than 175 ml, preferably less than 120 ml. The inlet funnel or heating chamber could comprise a fill level indicator to allow the user to see how much water they have poured into the heating chamber and/or to indicate whether the minimum fill volume of liquid has been introduced..

As mentioned previously apparatus in accordance with the invention may permit the automatic dispensing of the heated liquid under pressure generated during heating. In a set of preferred embodiments the apparatus comprises a dispensing chamber and a conduit for conveying water from the heating chamber to an inlet of said dispensing chamber. The heating chamber is preferably configured to heat a body of liquid, e.g. water, therein to boiling, with the increase in pressure associated with boiling forcing the heated liquid out of the heating chamber. In a preferred set of embodiments the heated liquid is forced into the conduit and vented into the dispensing chamber. This means that the dangerous pressurised boiling liquid and steam are safely ejected into the dispensing chamber whilst the liquid can be dispensed at the outlet in a slower, more uniform flow which is essentially independent of the liquid still coming in from the heating chamber. In other words, the dispensing chamber acts effectively to decouple the outlet from the heating chamber from the outlet to the user.

Since in preferred embodiments boiling liquid is forced under pressure into the conduit and into the dispensing chamber, the dispensing chamber could be provided at any convenient disposition relative to the heating chamber e.g. to the side of it or below it, but preferably the dispensing chamber is above the heating chamber. In a particularly preferred set of embodiments, the heating chamber and dispensing chamber are provided respectively in the lower and upper parts of an appliance.

The heater associated with the heating chamber could take any convenient form. It could, for example, comprise an immersion type heater or, preferably, a heater forming a wall of the heating chamber, preferably the base of the heating chamber. Indeed, in convenient embodiments the heater is substantially similar to that used in ordinary domestic kettles, e.g. with a sheathed resistance heating element bonded to the underside of the heater plate. In alternative embodiments a thick film heater could be employed.

An inlet funnel is provided for introducing liquid into the heating chamber through the aperture. The funnel could be open, but preferably the funnel is closed, e.g. with a lid. This prevents steam escaping from the appliance, e.g. in some embodiments which may be considered in which steam from the heating process is routed back to the inlet funnel, as well as preventing any debris falling into the inlet funnel. Preferably the heating chamber is below the funnel so that water can flow therein under gravity/hydrostatic pressure. It can therefore be seen that in these preferred embodiments a user is able to pour a volume of water, e.g. a cupful, into the funnel which is then admitted into the heating chamber through the aperture. In some embodiments the funnel comprises a water level indicator, which may be as simple as a graded scale printed on the outside of the funnel, which preferably is transparent or translucent. Preferably the volume of the funnel is arranged to be greater than or equal to the volume of the heating chamber. This allows the heating chamber to be filled completely by filling the funnel with water and not requiring the funnel to be refilled. The term 'funnel' is not intended to imply any particular shape and indeed it may have any shape that causes liquid introduced into the funnel to be directed into the aperture.

The heating chamber could be sealed during heating, apart from the conduit to the dispensing chamber. In a set of preferred embodiments however ventilation means are provided to the heating chamber. There are several potential benefits to this. One potential benefit is that the ventilation could reduce the build-up of pressure in the heating chamber during the initial stages of heating to prevent water being ejected from the conduit before it has been sufficiently heated. Another benefit is to vent away steam which can destabilise the valve means during the heating phase thus letting in cold water which would increase the boil time. Another potential benefit is that it can act to prevent a dangerous build-up of pressure in the heating chamber in the event that the outlet conduit becomes blocked for any reason. This function could be provided by a separate pressure relief valve, instead of, though preferably in addition to, the ventilation means. In a preferred set of embodiments the ventilation means is open to air. This can help in the smooth admission of water into the heating chamber from the reservoir by allowing the displaced air to escape.

The ventilation means could be arranged to vent to the exterior of the appliance but this is not considered ideal as it raises the possibility of steam being ejected near to a user. Preferably therefore it is vented to an airspace within the appliance. This could be a specially-designed space, but preferably the ventilation means is arranged to vent to the dispensing chamber where provided, or the inlet funnel, which for this reason is preferably covered, as discussed previously. The ventilation means preferably vents from the upper part of the heating chamber, most preferably from the upper surface thereof, i.e. it vents from the 'headspace' created when the heating chamber is filled with water, to try to ensure that gases rather than liquids are ejected from it.

Typically the dimensions of the ventilation means will be chosen so that when water in the chamber is first heated the pressure build-up therein is insufficient to eject it into the dispensing chamber, but as the water approaches boiling, sufficient pressure is developed in the heating chamber to eject the water through the conduit. The heating element could be energised by the act of pouring liquid into the funnel and thus filling the heating chamber. However preferably the heating element is energised by means of a user actuated switch. As mentioned previously, in accordance with preferred embodiments the liquid in the heating chamber is heated to boiling and thereby forced into the dispensing chamber via the conduit.

However, the applicant has recognised that since it is a relatively small volume of water being heated, the thermal inertia of a typical heating element, for example a sheathed element attached to the underside of the base of the heating chamber (a so called 'underfloor' heater) can become significant. However, by taking this into account, thermal stress on the element can be reduced by deliberately switching the element off before the liquid in the heating chamber reaches boiling point and relying on the residual heat in the element to bring the liquid to boiling and eject it. This reduces the risk of the element being energised without being in contact with liquid and therefore overheating. Alternatively or addition, the thermal stress on the element can be reduced by arranging the configuration of the heating chamber and the element switching-off mechanism such that a small volume of water is deliberately left remaining in the heating chamber after most of the heated water has been ejected. This remaining water acts to reduce the quench effect on the element and help prolong its life, particularly if fresh, colder liquid is added soon after.

Of course, the temperature at which the element needs to be switched off in order to achieve this effect is dependent on the liquid being heated, its volume and on the thermal mass of the element itself. Using a standard sheathed underfloor element and a heating chamber volume of approximately 200 ml, it has been found that the temperature of the water at which the element needs to be switched off is approximately 90°C. If this feature is employed the calculation could simply be carried out assuming that the heating chamber was filled to capacity. However more sophisticated embodiments are envisaged which measure and take into account the actual volume being heated to conserve energy even further.

In an alternative set of embodiments, the apparatus is configured to switch off the heating element in response to detection of another part of the heating and dispense cycle. In one set of embodiments the apparatus comprises means for switching off a heating element associated with the heating chamber responsive to the presence of at least one of water, steam, or an elevated temperature or pressure in the dispensing chamber. For example in one set of embodiments a steam-sensitive actuator is used to switch off the element e.g. using a conventional steam switch.

In one set of embodiments the apparatus is arranged to permit dispensing of the liquid in the dispensing chamber to be interrupted. This allows a user to prevent dispensing if he or she has forgotten to place the appropriate receptacle in place or otherwise suddenly needs to suspend use of the appliance. Preferably a user- operable valve is provided to close an outlet if required.

Having a valve provided somewhere in the outlet arrangement of the dispensing chamber, e.g. in the dispensing spout, could carry a disadvantage whereby for the next use the liquid retained in the dispensing chamber that had not been dispensed would be dispensed first into the user's receptacle and might, by then, have gone cold, thereby adversely affecting the average temperature of liquid dispensed the next time. However in some embodiments, the dispensing chamber comprises a drainage outlet which allows undispensed liquid to drain from it e.g. back into the heating chamber, the inlet funnel or a separate reservoir such as a drip tray. The latter option may be advantageous in avoiding a situation whereby for the next use more heated liquid is dispensed than the user had poured in.

The drainage outlet could be designed with a sufficiently low flow rate that it does not result in a significant amount of liquid draining out in the time-scale of a typical dispensing operation. For example, the drain outlet might be configured to have a flow rate that would drain the entire contents of the dispensing chamber over a period of time which is at least a minute and preferably more than two minutes. For example the drainage outlet could comprise a hole configured to be of suitable size and shape to give a sufficiently low drainage rate but high enough to prevent a meniscus forming over the hole which effectively prevents any drainage.

Alternatively and preferably the drainage outlet comprises a valve. This could be triggered to be opened automatically by a timer or upon some other condition being met. In a set of preferred embodiments the drainage valve is coupled to the valve means controlling the dispensing of liquid from the chamber. This allows the drainage valve to be closed when the dispensing chamber is dispensing, and open when dispensing has finished so that liquid is not retained in the dispensing chamber unnecessarily but equally it does not leak out during dispensing.

Accordingly the drainage valve can be configured to allow rapid drainage of any liquid remaining in the dispensing chamber when opened. In convenient embodiments a diverter valve is provided which can direct liquid flow either to a dispense outlet or to a drainage outlet.

In some embodiments the inlet to the dispensing chamber is arranged so that any steam which is generated in the heating chamber and passes along the conduit, passes through the water or other liquid which is already held in the dispensing chamber. This has two advantages. Firstly, the steam passing through the water in the dispensing chamber provides additional heat to it as the steam condenses. This helps to raise the bulk temperature of the water in the dispensing chamber, thus countering the negative effect of the first volume of water exiting the heating chamber which may not be at the target temperature.

The second advantage of the arrangement described above is that since steam which exits the heating chamber passes through the water and so condenses, there is a much lower risk of steam being ejected through the ultimate spout of the device and therefore into possible contact with the user. Consequently, the heating chamber can be configured to heat the water to a higher temperature than is possible in a tubular flow heater, i.e. it is more feasible to heat the water to boiling such that steam is produced since the deleterious effects of steam on tubular flow heater arrangements are not a factor to the same extent in arrangements in accordance with embodiments of the invention. The combined effect of these is that in preferred embodiments of the invention, a small amount of liquid, e.g. a cupful, can be delivered to a user virtually at boiling temperature whilst without the risk of steam being ejected along with the water.

Although the dispensing chamber is preferably configured such that steam exiting the inlet arrangement of the dispensing chamber re-condenses, e.g. during its passage through the liquid held in the chamber, it is likely that some steam will pass up into the space above the liquid. It is preferred therefore that the dispensing chamber has one or more ventilation outlets on the upper part thereof to prevent the build-up of pressure above the retained liquid. This has the advantages that enough steam reaches the steam switch and also prevents the dispense rate from being too fast. The one or more ventilation outlets could vent straight to air, or they could vent into the inlet funnel.

Certain preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Fig. 1 is a perspective view of an embodiment of a liquid heating apparatus in accordance with the invention;

Fig. 2 is a perspective view of the upper surface of the heating chamber of the apparatus;

Fig. 3 is a perspective view of the lower surface of the heating chamber; and Figs. 4a, 4b, 5a and 5b are sectional views through the heating chamber.

Fig. 1 shows a hot water dispensing apparatus 1 which has a heating chamber 2 in the lower part of the apparatus. A heating element 4 and a control 6 are located underneath the heating chamber 2 and will be described in more detail with reference to Fig. 3. In the upper part of the apparatus is located a dispensing chamber 8 from which hot water is dispensed out of an outlet pipe 10 which depends down from the dispensing chamber 8 to allow a cup 12 to be filled with hot water. The heating chamber 2 is in fluid communication with the dispensing chamber 8 via a dispensing conduit 14 and a ventilation pipe 16. In the dispensing chamber is one of the applicant's standard R48 steam switches (not shown) which is more commonly used in domestic kettles for automatically switching them off when boiled. As is well known to those skilled in the art this comprises a snap acting bimetallic actuator which acts on a rocker arm that moves over-centre to open a set of electrical contacts. A funnel 18 above the heating chamber 2 is in fluid communication with the heating chamber 2 via an inlet pipe 20 which allows the heating chamber to receive water poured into the funnel 18. The dispensing chamber 8 has a further ventilation pipe 22 from its upper volume into the funnel 18.

Fig. 2 shows the heating chamber 2 from above from where apertures 24, 26 and 28 which connect with the inlet pipe 20, the dispensing conduit 14 and the ventilation pipe 16 respectively can be seen in the heating chamber cover member 30. The central aperture 24 connects to the bottom of the inlet pipe 20 from the funnel 18. Away from the centre of the heating chamber is the aperture 26 which connects with the dispensing conduit 14 and from there the dispensing chamber 8. Also away from the centre of the heating chamber 2 is the aperture 28 which connects with the ventilation pipe 16 that vents to the dispensing chamber 8.

Alternatively the ventilation pipe 16 could vent to the inlet funnel 18. Towards the periphery of the heating chamber 2 is a pressure relief valve 32 which allows the release of pressure from the heating chamber 2 in the event of a dangerous buildup of pressure. This could be arranged for example to vent into a suitable part of the interior of a casing (not shown), e.g. the dispensing chamber or inlet funnel. In alternative embodiments a further tube communicating with the dispensing chamber could be provided to allow for the safe escape of steam. In this case the pressure relief valve could be at the lower (heating chamber) end of the tube, the upper (dispensing chamber) end of the tube or anywhere inbetween.

Fig. 3 shows the heating chamber 2 from below from where the heating element 4 and control 6 can be seen in more detail. The heating element 4 is a conventional arcuate sheathed heating element which connects to the power supply via cold tails at each end. The heating element 4 is attached to the underside of the heating chamber 2 so that it is in thermal communication with the heating chamber 2. The control 6 controls the energising of the heating element 4 and is conveniently a variant of one of the applicant's U series of controls developed for kettles (further details of which are disclosed in WO 95/34187). The control 6 is mounted on the underside of the heating chamber 2.

Fig. 4a shows a sectional view of the heating chamber 2 which illustrates the details of the apertures 24 and 26 for the inlet pipe 20 and the dispensing conduit 14. Fig. 4b shows a close up view of the apertures 24 and 26. The heating chamber cover member 30 has a circular central aperture 24 defined therein, with the inlet pipe 20 depending downwards a short distance into the heating chamber 2. At the distal end of the inlet pipe 20, within the heating chamber 2, is a circular seal 33. A series of three integrally moulded and circumferentially spaced legs 34 depend

downwardly from the lower surface of the heating chamber cover member 30. Attached to distal end of each leg 34 by means of rivets 36 is a retaining member 38.

The legs 34 and the retaining member 38 between them define a cylindrical space in which a buoyant frusto-conical valve member 40 can rise and fall over a short vertical travel. In the lower position depicted in Figs. 4a and 4b, water can clearly pass through the aperture 24 from the funnel 18 into the heating chamber 2.

On the left-hand side of Figs. 4a and 4b is a vertically extending cylindrical outlet tube 42, the upper end of which receives the lower end of the dispensing conduit 14. The lower end of the vertical outlet tube 42 is received by a foot member 44 which is castellated around its lower edge in order to allow the passage of water and steam between the castellations whilst acting as a coarse filter against the ingress of e.g. large pieces of scale etc. The vertical outlet tube 42 is moulded into the aperture 26 in the upper surface of the heating chamber cover member 30. The arrangement shown in this embodiment seeks to maximise the amount of water ejected from the heating chamber.

Figs. 5a and 5b show sectional views of the heating chamber 2 which illustrate the details of the apertures 24 and 28 for the inlet pipe 20 and the ventilation pipe 16. Fig. 4b shows a close up view of the apertures 24 and 28. The central aperture 24 has already been described with reference to Figs. 4a and 4b. On the right-hand side of Figs. 5a and 5b in a raised portion 48 of the heating chamber cover member 30 is the aperture 28 which connects to the ventilation pipe 16. This aperture 28 is narrower than the apertures 24 and 26 for the inlet pipe 20 and dispensing conduit 14.

Operation of the apparatus 1 will now be described with reference to the figures.

Initially, the apparatus 1 is filled with water, conveniently by pouring a cupful of water into the funnel 18. The volume of water is determined by the size of the cup, thereby ensuring that the volume of water heated and dispensed will suit the size of the cup, to make a hot drink for example. The heating chamber 2 is initially empty, and the valve member 40 is resting at its lowest position on the retaining member 38 between the legs 34 of the valve mechanism. Water is therefore admitted to the heating chamber 2 until a minimum level of water in the heating chamber 2 is reached, i.e. when the valve member 40 becomes buoyant and floats up to its upper position between the legs 34 to close the aperture 24 of the inlet pipe 20. However, the buoyancy of the valve member 40 is chosen to be such that as water continues to be kept being poured through the funnel, the weight of the water on the valve member 40 overcomes its buoyancy and reopens the aperture 24 thus allowing more water to be admitted to the heating chamber 2.

Once the cup has been emptied into the funnel 18 and admitted to the heating chamber 2, the buoyancy of the valve member 40 once again causes it rest against the seal 33 and so close the aperture 24 of the inlet pipe 20. The user then places the cup 12 underneath the outlet tube 10 switches on the heating element 4 which rapidly heats the relatively small volume of water in the heating chamber 2. An interlock or micro-switch could be provided to prevent the element being energised until a cup or other receptacle is in place.

As the water is heated, the pressure in the heating chamber 2 begins to increase. On one hand this serves to provide further closure pressure for the valve member 40 against the circular seal 33 of the aperture 24 for the inlet pipe 20 and thereby prevents steam or spitting water being ejected into the funnel 18. However the ventilation tube 16 limits the build-up of pressure somewhat.

As the water in the chamber 2 reaches boiling point, the pressure in the chamber increases rapidly as steam is produced. This pressure forces the boiling water from the heating chamber 2 up the outlet tube 42 into the dispensing conduit 14 and then into the dispensing chamber 8. The steam associated with the boiling water in the dispensing chamber 8 activates the steam switch, which removes power to the heating element 4. Once the water has been ejected into the dispensing chamber 8, it is dispensed out of the outlet pipe 10 and into the cup 12.

Thus in the embodiment described above it can be appreciated that in a very short period of time a quantity of water, the volume determined by the amount of water a user pours into the heating chamber 2, is heated to boiling and dispensed through an outlet tube 10 in a safe and controlled manner. This can be achieved despite the water being heated fully to boiling point and moreover despite the inevitable mixing with a small quantity of water that did not reach boiling point. The negative effect of such cooler water is ameliorated by passing steam generated at the end of the boiling process through it prior to it being dispensed. The steam condenses and brings the bulk temperature of the water substantially or completely back to boiling point. Thus the water dispensed to the user is at least substantially at boiling point and can therefore be used for any application where boiling water is required e.g. for making tea.

It will be appreciated by those skilled in the art that the embodiment described above is only one example of the many possible ways in which the invention can be implemented. For example, although the embodiments have been described for producing boiling water, the invention may also be applied to the heating of other liquids e.g. brewed beverages such as tea or coffee or perhaps heated milk for use in beverages. Furthermore, although the embodiments described combine several advantageous features, it is not considered essential for all of these features to be provided together.

Claims

1. A liquid heating apparatus for heating a variable volume of liquid comprising: a heating chamber;

2. A liquid heating apparatus as claimed in claim 1 , wherein the valve means comprises a buoyant valve member arranged such that a predetermined minimum level of liquid in the heating chamber brings the valve means into the semi-closed configuration.

3. A liquid heating apparatus as claimed in claim 2, wherein the predetermined minimum volume of water is less than 250 ml, preferably less than 175 ml, preferably less than 120 ml.

4. A liquid heating apparatus as claimed in claim 1 , 2 or 3, wherein the maximum volume of water the heating chamber can heat is at least 400 ml, preferably at least 500 ml.

5. A liquid heating apparatus as claimed in claim 2, 3 or 4, wherein the buoyancy of the valve member is arranged such that the pressure of liquid in the inlet funnel is able to displace it sufficiently to permit the heating chamber to be filled beyond the predetermined minimum level.

6. A liquid heating apparatus as claimed in any of claims 2 to 5, wherein the buoyant valve member comprises a freely floating valve member.

7. A liquid heating apparatus as claimed in claim 6, wherein the freely floating valve member is received in a housing which permits liquid flow through it but retains the valve member, the valve member having an upper position corresponding to the semi-closed configuration in which it is against a valve seat and a lower position where it is retained in the lower part of the housing.

8. A liquid heating apparatus as claimed in claim 6 or 7, wherein the freely floating valve member is downwardly tapering, e.g. frusto-conical.

9. A liquid heating apparatus as claimed in any preceding claim, wherein the valve means is configured such that increasing pressure in the heating chamber during heating forces the valve closed.

10. A liquid heating apparatus as claimed in claim 9, wherein the valve member is arranged to be pressed against a sealing surface by internal pressure in the heating chamber during heating.

1 1 . A liquid heating apparatus as claimed in claim 10, wherein the sealing surface is located in the lower half of the heating chamber and defines a or the predetermined minimum fill level.

12. A liquid heating apparatus as claimed in any preceding claim, wherein the heating chamber is configured to heat a body of liquid therein to boiling, with the increase in pressure associated with boiling forcing the heated liquid out of the heating chamber.

13. A liquid heating apparatus as claimed in claim 12, wherein the heated liquid is forced into the conduit and vented into the dispensing chamber.

14. A liquid heating apparatus as claimed in any preceding claim, comprising a dispensing chamber and a conduit for conveying water from the heating chamber to an inlet of said dispensing chamber.

15. A liquid heating apparatus as claimed in claim 14, wherein the dispensing chamber is above the heating chamber.

16. A liquid heating apparatus as claimed in claim 14 or 15, wherein the apparatus is arranged to permit dispensing of liquid from the dispensing chamber to be interrupted.

17. A liquid heating apparatus as claimed in claim 14, 15 or 16, wherein the inlet to the dispensing chamber is arranged so that any steam which is generated in the heating chamber and passes along the conduit, passes through the water or other liquid which is already held in the dispensing chamber.

18. A liquid heating apparatus as claimed in any of claims 14 to 17, wherein the dispensing chamber comprises one or more ventilation outlets on the upper part thereof to prevent the build-up of pressure above the retained liquid.

19. A liquid heating apparatus as claimed in any preceding claim, comprising a heater forming a wall of the heating chamber, preferably the base of the heating chamber.

20. A liquid heating apparatus as claimed in claim 19, wherein the heater comprises a sheathed heating element.

21 . A liquid heating apparatus as claimed in any preceding claim, wherein the heating chamber is below the inlet funnel.

22. A liquid heating apparatus as claimed in any preceding claim, wherein the volume of the funnel is arranged to be greater than or equal to the volume of the heating chamber.

23. A liquid heating apparatus as claimed in any preceding claim, wherein ventilation means are provided to the heating chamber.

24. A liquid heating apparatus as claimed in claim 23, wherein the ventilation means is open to air.

25. A liquid heating apparatus as claimed in claim 24, wherein the ventilation means is vented to an airspace within the appliance.

26. A liquid heating apparatus as claimed in claim 23, 24 or 25, wherein the ventilation means vents from the upper part of the heating chamber, preferably from the upper surface thereof.

27. A liquid heating apparatus as claimed in any preceding claim, comprising means for switching off a heating element associated with the heating chamber responsive to the presence of at least one of water, steam, or an elevated temperature or pressure in the dispensing chamber.