temperatures below boiling and particularly to apparatus which can provide a sterilised liquid output, for example warm water for use in the preparation of infant formula milk or other infant food.

Presently dried infant milk or infant food is typically reconstituted by boiling water in a kettle in order to sterilise it and then allowing the water to cool to a temperature suitable for giving to the infant - e.g. typically approximately body temperature or a few degrees higher. However, this is a time-consuming operation and it can be difficult to judge the correct temperature accurately.

When viewed from a first aspect the present invention provides an apparatus for providing a warmed liquid, comprising heating means for heating said liquid to a first temperature, cooling means for cooling said liquid to a second, lower temperature and an outlet for dispensing said liquid after it has been cooled, wherein the apparatus is further configured to pass a sterilising fluid through at least said cooling means in order to sterilise the cooling means prior to dispensing said liquid.

When viewed from a second aspect the present invention provides a method of operating an apparatus comprising heating means and cooling means to provide a warm liquid, said method comprising the steps of:

passing a sterilising fluid through at least said cooling means in order to sterilise the cooling means prior to dispensing said liquid;

passing a liquid from a reservoir to said heating means and heating said liquid to a first temperature,

passing said liquid through said cooling means thereby cooling it to a second temperature: and

dispensing said cooled liquid through an outlet.

Thus it will be seen by those skilled in the art that in accordance with the present invention a liquid such as water can be heated to a high temperature in order to sterilise it and then cooled automatically within the apparatus prior to dispensing, with the cooling means itself being sterilised before dispensing takes place. This allows the liquid to be delivered at an appropriate temperature without loss of sterility and in less time than it would take the liquid simply to cool naturally.

The cooling means could take one of several forms: for example it could comprise a heat sink - e.g. with cooling fins, a fan or other means to produce a forced air flow, a solid state cooling device such as a Peltier device, a closed loop refrigerant system or any combination of the above.

In a set of preferred embodiments, however, the cooling means comprises a heat exchanger, the other side of which is in communication with a liquid reservoir for supplying the heating means. This arrangement is advantageous in minimising the requirement for additional components and therefore the cost, and also in maximising the efficiency of the device since the heat extracted from the liquid being cooled is used to preheat the liquid before it is heated to the first temperature.

The sterilising fluid could be a liquid or gaseous substance provided specifically for the purpose and contained in a suitable reservoir within the apparatus. In a set of preferred embodiments, however, the sterilising fluid comprises steam or hot liquid produced by heating the liquid, preferably with the recited heating means (as opposed to a separate heater). This could be achieved, for example, by operating the apparatus as it is normally operated when dispensing liquid except to disable the cooling means so that all of the cooling means can be allowed to reach a temperature sufficient to sterilise it. In one set of embodiments a quantity of water is heated to boiling by the heating means and a steam pressure allowed to develop as a result which is sufficient to force steam through the cooling means.

Where pre-dispensing sterilisation is carried out based on heat, the amount of time necessary will be dependent on the temperature. For example if steam is being used, it may be sufficient for all relevant parts to reach the temperature of the steam briefly. Alternatively a temperature of 70°C may be sufficient but would need to be maintained for longer - e.g. 30 seconds. In both cases the sterilisation could simply be carried out for a predetermined time but in one set of embodiments, temperature sensing means are provided at a suitable point on the apparatus in order to allow for detection of the desired temperature being reached. Typically such temperature sensing means would be located at a point most fluidly or thermally distant from the heating means such that detection of the required temperature there ensures that all of the appropriate parts of the system have reached the required temperature. The steam or other sterilising fluid may, in some embodiments, sterilise the cooling means and any associated inlet and outlet conduits but not all the way to the dispensing outlet. For example the sterilising fluid may be diverted to a sump or reservoir - which in the case of the sterilising fluid being derived from the liquid to be dispensed, could be the main reservoir for that liquid. In such cases it might be intended that the apparatus be configured so that e.g. an outlet nozzle is sterilised by other means - such as by allowing it to be removable for sterilisation separately by a user.

In other embodiments, however, the sterilising fluid may be allowed to pass all the way to the dispensing outlet in order to sterilise that too. This is

advantageous in avoiding the user having to sterilise it. There is a further potential advantage in accordance with a set of embodiments in which the apparatus is arranged to dispense at least some of the sterilising fluid into a user's receptacle. The advantage of this is that it can be used to sterilise the receptacle or its contents. For example if steam is used to sterilise the cooling means, it can also be used to sterilise a user's baby bottle. Alternatively if water heated to 70°C is used for example, this water, or some of it, could actually be used as part of the water needed to mix with the milk powder. This is beneficial as it helps to compensate for loss of sterility through use of powder from an opened container.

The sterilising fluid need not all be directed to the same place: some could be dispensed through the outlet and some returned to the reservoir. This could be achieved by only opening a corresponding valve at the outlet part-way and/or by opening it only for part of the sterilisation cycle.

In one set of preferred embodiments a valve is operated to direct steam into a receptacle such as a baby bottle for the last part of the sterilisation phase.

Advantageously in such embodiments ordinary liquid dispensing is then

commenced, the first part of which is at an elevated temperature compared to the equilibrium dispense temperature. The reason for this is that the cooling means is still at an elevated temperature following the steam sterilisation. The outlet liquid temperature may therefore be allowed to reduce to equilibrium at a natural rate rather than trying to achieve equilibrium as quickly as possible by controlling the flow rate using a feed-back loop. This enables the bottle and formula powder to be more fully sterilised. As mentioned above, the equilibrium temperature may be chosen to take the initially higher temperature into account. In some embodiments in which steam or other fluid at elevated temperature is supplied for sterilising a bottle prior to dispensing, the apparatus may be provided with means for interrupting its operation prior to dispensing the warm liquid. This allows the user add formula powder to the bottle if not already done, shake the bottle, stir the bottle etc.

In a set of embodiments in which steam or other fluid at elevated temperature is supplied for sterilising a bottle prior to dispensing, a separate outlet could be provided for this purpose or a single outlet could be provided for both sterilisation and subsequent liquid dispensing.

In a preferred set of embodiments, the apparatus comprises an

automatically-controlled valve which may be opened or closed to permit or prevent respectively dispensing of liquid via the dispensing outlet. This can be used to ensure that liquid is only dispensed at the appropriate temperature, which is of course important in applications where it is to be used for infant feed. Such a valve can advantageously also be used during the sterilisation phase either to permit steam or other sterilising fluid to pass through the outlet (in order to sterilise it), or to prevent it from doing so (if the outlet is sterilised by other means).

In some embodiments a divert valve is provided upstream of the outlet in order to allow liquid which has not been dispensed to be drained into a suitable reservoir. Allowing draining of the system in this way is beneficial in facilitating sterilisation of the cooling means and possibly other parts of the apparatus in the next operation.

Similarly, in a set of preferred embodiments, the cooling means and the parts of the system downstream are arranged such that liquid therein can drain out automatically - either via the outlet or to a reservoir such as the main water reservoir. This ensures that any condensation which forms during the sterilisation procedure does not collect, but rather is allowed to drain out. In one potential arrangement a fluid return path is provided for returning fluid to the reservoir or a further reservoir which does not pass out of the outlet. Preferably the fluid return path is arranged so as to collect condensate formed within the cooling means. The fluid return path is preferably controlled by a valve so as selectively to permit liquid or steam to pass out of the outlet or through the return path. Preferably the valve and outlet are so arranged that condensate forming in the cooling means drains towards the valve rather than the outlet even when the valve is set to allow heated liquid or steam out of the outlet. Advantageously, the cooling means is provided with an inlet which is configured to allow air displaced by liquid entering the cooling means to exit therethrough. This can conveniently be achieved simply by ensuring that cross- sectional area of the inlet is sufficiently large. In one example, the inlet has a diameter of greater than 10 mm or greater than 12 mm to ensure this.

In accordance with the invention, liquid is heated to a first temperature before being cooled to a second temperature and dispensed. The first temperature can be chosen to suit the application and need not be boiling. In preferred embodiments however, the heating means is adapted to heat the liquid to boiling, at least during a dispensing phase of operation.

The heating means could be a batch heater in which the required volume of liquid is heated to the first temperature before exiting the heating means.

Preferably, however, the heating means comprises a flow heater in which liquid is permitted to enter and exit the heating means while heating is taking place. One example of such a flow heater is the "dual tube" variety in which a liquid conduit and a tube containing a sheathed heating element are provided adjacent one another.

There is, however, a problem with conventional flow heater arrangements in that they cannot satisfactorily produce boiling water since if any significant localised boiling occurs, it gives rise to hot-spots on the heated surface as a result of the absence of liquid on that part of the surface, and the phenomenon of spitting whereby the steam pressure drives water out of the tube which has not yet been fully heated. These are problems in all conventional flow heaters since steam is produced locally at the heater surface significantly before the bulk water

temperature has reached boiling. For example, these problems can arise if the bulk water temperature goes above about 85°C.

In a set of preferred embodiments, the heating means comprises a flow heater having a boiling zone in which steam escaping from the liquid being heated is permitted to exit separately from the heated liquid. Preferably, the heater is arranged such that liquid exits the boiling zone automatically upon reaching a predetermined level. This is achieved in preferred embodiments by weir means at the liquid outlet so that when the predetermined level is reached, the liquid spills over the weir and is able to exit the boiling zone.

Such an arrangement is novel and inventive in its own right and thus when viewed from a further aspect the invention provides a liquid heating apparatus comprising a heating chamber having an electric heating element for heating liquid therein to boiling or near boiling, said heating chamber comprising a space above the liquid surface for allowing the escape of steam from the liquid surface; a liquid inlet for allowing liquid into the heating chamber; a liquid outlet configured to maintain a substantially constant level of liquid as the inlet flow rate varies between a predetermined maximum and a predetermined minimum; and means downstream of the heating chamber for cooling said liquid.

Embodiments of the invention which comprise a heater having a

substantially constant level of liquid in the heating chamber are preferably operable in a sterilisation mode in which the heating chamber is filled with a volume of liquid which is insufficient to bring the level of liquid in the heating chamber to said substantially constant level. In such arrangements the water does not leave the water outlet, but it is boiled and so produces steam which can act as the sterilising fluid. The steam exits the water outlet and therefore passes into the cooling means in order to sterilise it.

In preferred embodiments the heating means comprises a heating element formed on or mounted to the underside of a heater plate. The heating element could, for example, comprise a sheathed heating element mounted to the plate, or a thick film element formed on or mounted to the plate.

Preferably the apparatus is adapted to dispense water at a temperature of between 30 and 50°C, more preferably between 35 and 45°C. Preferably the apparatus is provided with temperature sensing means at the outlet in order to allow control of the outlet temperature. In one set of embodiments, control over the outlet temperature is exercised by controlling the rate of flow of liquid into the heating means. This could be controlled either by a suitable valve (which could be a valve previously mentioned) or by altering the speed of a pump. As previously mentioned, in some embodiments the outlet temperature is varied during the dispense cycle. Where the volume of liquid to be dispensed is known, it can still be ensured that the overall average temperature has the desired value.

In some embodiments, the apparatus is provided with level detecting means for detecting when the cooling means is filled to a predetermined level. This conveniently allows dispensing to be delayed until the cooling means is operating adequately efficiently. Preferably the level detecting means detects when the cooling means is filled sufficiently that the liquid is backed up to the outlet of the heating means. In one set of embodiments, the level detecting means comprises an electrically conductive portion of the casing of a temperature sensor such as a thermistor. This allows a single component to provide a dual function of detecting the temperature of liquid at the outlet of the heating means and detecting the presence or absence of liquid which has backed up from the cooling means.

In some other embodiments the apparatus is arranged so that dispensing cannot commence until the cooling means has been adequately filled. Preferably this is achieved by arranging the dispense outlet at height relative to the cooling means such that a predetermined liquid level in the cooling means or upstream thereof is necessary to give sufficient hydrostatic pressure to dispense liquid. In practice the outlet height is likely to be a little lower than the aforementioned predetermined liquid level to account for pressure losses in the cooling means and elsewhere in the system.

For the avoidance of doubt, disclosure of any preferred feature in the context of any embodiment of the invention is not intended to limit that feature to that particular embodiment and all features should be considered to be mutually interchangeable between embodiments.

As used herein the term sterilisation is intended to refer to the process of killing potentially harmful bacteria and germs. It should not be interpreted as implying a particular level of sterility - e.g. meeting a definition of clinically sterile or indeed any other particular definition or effectiveness.

Certain 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 highly schematic diagram illustrating the principle features of an embodiment of the invention;

Fig. 2 is a perspective view of the major components of the heating and cooling system;

Fig. 3 is an exploded, cross-sectional view of the heating chamber shown in

Fig. 2;

Fig. 4 is a perspective view from beneath of the upper housing of the heating chamber;

Fig. 5 is a perspective view of the upper housing member from above;

Fig. 6 is a sectional view through the heat exchanger;

Fig. 7 is a highly schematic diagram illustrating the principle features of another embodiment of the invention; and

Figs. 8a to 8d are schematic illustrations showing the operation of the valve arrangement of Fig. 7. Considering first Fig. 1 , there may be seen a schematic representation of an apparatus for producing warm, sterilised water suitable for preparing infant feed. On the lower part of the diagram is a cold water storage reservoir 2 having an outlet 4 communicating with a pump 6. Although not shown, the reservoir may be provided with a filter cartridge such as one of the Applicant's Aqua Optima

(registered trade mark) water cartridges.

On the outlet side of the pump 6, a conduit 8 communicates with the inlet 10 of the cold side of a heat exchanger 12. The heat exchanger is described in greater detail hereinbelow with reference to Fig. 6. The outlet 14 of the cold side of the heat exchanger 12 is connected to an inlet tube 16 of the heating chamber 18. The heating chamber 18 is described in greater detail hereinbelow with reference to Figs. 3 to 5. The heat exchanger 12 and heating chamber 18 may also be seen, in isolation, in Fig. 2.

The heating chamber 18 is provided with a sheathed heating element 19 on the underside thereof as may be seen in further detail in Figs. 3 to 5 as mentioned above. The liquid outlet 20 of the heating chamber is connected to the inlet 22 of the hot side of the heat exchanger 12. A temperature sensor, e.g. a thermistor is disposed in the heating chamber outlet 20, the purpose of which will be described later. A further outlet 26 is provided at the top of the heating chamber which is closed by a pressure valve 28 which could comprise a weight, spring bias, or a combination thereof. Although not shown, a small bleed drain aperture could be provided in the heating chamber to allow the chamber to empty back into the reservoir 2 between uses.

The outlet 30 of the hot side of the heat exchanger 12 is connected to a diverter valve arrangement 32 which is able selectively to communicate the outlet 30 with an external dispensing nozzle 34 or a drain tube 36 which is directed into the cold water reservoir 2. A further temperature sensor, e.g. a thermistor, is provided at the outlet 30 of the hot side of the heat exchanger. The cold water pump 6, the heating element 19, the temperature sensors 24, 38 and the diverter valve arrangement 32 are all connected to a control circuit (not shown).

As mentioned above, Fig. 2 shows in isolation the heat exchanger 12 and heating chamber 18 some of the inlets and outlets of these parts are shown using the same reference numerals as used in Fig. 1 , although the connections between them are not shown. Fig. 3 is an exploded and sectioned view of the heating chamber 18. From this it may be seen between an upper housing part 40 which is closed off from below by a circular and substantially planar heater plate 42.

The heater plate 42 is sealed to the upper housing part 40 by means of a peripheral annular channel 44 which receives a corresponding annular downwardly depending wall portion 48 of the upper housing part 40, with the walls of the channel 44 being clamped or crimped to retain the downwardly depending wall portion 48 securely. An annular seal 50 is provided in the channel 44 between the inner wall of the channel and the downwardly depending wall portion 48. In other words, the heater plate 42 is attached to the upper housing part 40 using the applicant's well-established Sure Seal sealing system. Of course, any other suitable sealing system could be employed instead.

A conventional sheathed heating element 19 is attached to an aluminium heat diffuser plate 52 which is, in turn, fixed to the underside of the heater plate 42.

The liquid outlet of the heating chamber comprises a cylindrical tube 20 which projects through the plate 42 so as to be somewhat proud of the heater surface. This effectively forms a weir so that when the liquid level inside the heating chamber reaches the top of the outlet tube 20, it tends to overflow down into it.

The upper housing part 40 will now be described with continuing reference to Fig. 3 but also with reference to Figs. 4 and 5. From these Figures it may be seen that the upper housing part 40 comprises a further downwardly depending wall 54 which, as may be seen most clearly in Fig. 4 is approximately Omega shaped. As Fig. 3 shows, the opening formed by the shape of the wall is located in the vicinity of the liquid outlet 20. Diametrically opposite to this, there is an indented portion of the wall 54a which accommodates the water inlet tube 16. The wall 54 thus creates two semi-circular channels on either side of the inlet 16 around which water entering through the inlet 16 must pass before it reaches the outlet 20. The position of the wall 54 means that the two semi-circular channels which are formed are substantially aligned with the heating element 19 provided on the underside of the plate 42. A connector 58 for the inlet tube 16 is provided on the outer face of the upper housing part 40. The connector 58 receives the end of a connecting hose (not shown) connected to the cold side outlet 14 of the heat exchanger.

Fig. 6 shows a cross section through the heat exchanger 12. As may be seen, the heat exchanger comprises a stack of six alternating interleaved plates 66, 68. The top-most plate 66a defines (together with a cover, not shown) a chamber in the cold side of the heat exchanger. This is the first such chamber encountered by the cold water entering the cold water inlet 10, the mouth 70 of which opens into the chamber. Water entering from the mouth of the inlet tube 70 spreads across the surface of the plate 66a to exit the chamber through an outlet 71 in the diagonally opposite corner from where it passes into the next chamber formed between the second and third plates 68a and 66b. The water then flows in the opposite direction in this chamber through an outlet vertically aligned with the inlet 70 above and from there into the final chamber formed between third and fourth plates 68b and 66c. It then flows out of here through the cold side outlet 14.

The chambers formed alternate between those on the heating side of the heat exchanger make up the cooling side of the exchanger. These are arranged so that water flows from the hot water inlet 22, through the three interleaved chambers to the outlet 30. The plates are designed so that the water flows in opposite directions in adjacent chambers and so that water near the inlet end of the cold side of the exchanger is near the water at the outlet end of the hot side of the exchanger and vice versa. The plates 66, 68 are typically made of thin, non-corrosive material e.g. stainless steel.

Operation of the apparatus will now be described with reference to all of the Figures. The apparatus has three distinctive phases of operation. Initially, a user ensures that the cold water reservoir is adequately filled with cold water (or in another embodiment the device could be permanently plumbed in). When the user presses a button to request warm water, a sterilisation phase is commenced. In this phase, the pump 6 is operated for a fixed amount of time in order to deliver a fixed amount of water via the cold side 10-14 of the heat exchanger through the inlet 16 and into the heating chamber 18. The amount of water delivered into the heating chamber 18 is sufficient to cover the portion of the heater plate directly above the element 19 but is not sufficient to overflow into the outlet 20.

Once the desired amount of water has been delivered, the pump 6 is switched off and the heater 19 is energised to heat the water to boiling (these two operations could overlap however - i.e. the heater could be energised before the pump is switched off). As the water approaches boiling, steam is generated in the heating chamber 18, raising the pressure therein and forcing the steam out of the outlet 20 and into the hot side 22, 30 of the heat exchanger and from there via the diverter valve 32 to the outlet nozzle 34. The valve 28 on the steam outlet 26 ensures that the pressure inside the heating chamber 18 is not allowed to rise too far.

The heating element 19 is energised so as to continue to produce steam until either a predetermined temperature is detected by the outlet temperature sensor 38 or after a predefined temperature has been exceeded for a

predetermined amount of time. This ensures that the whole of the cooling side of the system is suitably sterilised. For example, the sterilisation may be satisfactorily achieved by ensuring that all parts of the system reach 100°C, or that a

temperature of 70°C is maintained for 30 seconds. The vertical arrangement of the heat exchanger 12 and the configuration of the connecting pipes means that the heat exchanger and the valve arrangement 32 downstream of it are free-draining so that condensate forming within any of these parts can freely exit e.g. drip tray (not shown) beneath the outlet nozzle 34.

In an alternative embodiment, the diverter valve 32 is set to divert the steam to the drain pipe 36 and therefore back into the water reservoir 2. This has the advantage of avoiding steam exiting in the vicinity of a user, but means that the outlet nozzle 34 must be separately sterilised.

Once sterilisation is complete, the apparatus enters its second, pre- dispense mode. The pump 6 is once again operated to pump cold water into the heating chamber 18 via the heat exchanger 12. In this phase, however, the pump 6 is operated continuously so that the water in the heating chamber 18 overflows the top of the outlet tube 20 and thus starts to fill the hot side of the heat exchanger 12, via the inlet 22. At the same time, the heater 19 is energised so that the water in the heating chamber 18 is heated to boiling or near boiling by the time it exits the chamber through the outlet 20. The rate at which the water is pumped by the pump 6 and/or the power of the heating element 19 are modulated to maintain boiling at the outlet 20 at all times whilst producing only a modest amount of excess steam.

The outlet valve 32 is closed either fully or partially so that the water backs up in the heat exchanger until it reaches nearly the top of the outlet tube 20 of the heating chamber. This can be detected by an electrical conductivity level detection circuit (not shown) that comprises a conductive electrode formed by the stainless steel sheath of the temperature sensor 24 which is positioned close to the heater outlet 20. The diameter of the outlet 20 and the hose connecting this to the heat exchanger inlet 22 is of sufficient diameter, e.g. greater than 12 mm, to ensure that the heat exchanger is flooded and that any air is allowed to escape back up into the heating chamber. This is advantageous in avoiding air remaining on the surfaces of the heat exchanger 12 which would otherwise compromise the heat transfer efficiency which it could achieve.

Once the temperature sensor 24 has determined that the heat exchanger 12 is flooded, the pre-dispense stage is finished and the dispense stage commenced. In this stage, the outlet valve 32 is arranged to direct the water from the outlet 30 of the hot side of heat exchanger to dispensing nozzle 34. The flow rate of the cold water pump 6 is now controlled by the temperature of the outlet temperature sensor 38 to maintain the optimum dispensed temperature. The power of the heating element can be fixed, in which case it should normally be sufficient to match the flow rate of the water and ensure that it is brought to boiling under the "worst case" circumstances. Alternatively, it can be controlled to boil the water and provide a small safety margin in the form of excess steam production, which can be allowed to exit via the steam outlet 26 with the valve 28 being opened during this phase.

To give some examples of temperatures, the cold water in the reservoir 2 may be at 20°C and may be heated via its passage through the heat exchanger 12 to 80°C. The heating chamber 18 then raises the temperature of the water from 80°C to boiling or near boiling (e.g. 99°C+), from which it passes through the hot side of the heat exchanger 12 to be reduced in temperature to approximately 40°C. This is an ideal temperature for producing baby milk since generally a temperature of 38°C is considered ideal for a baby bottle and a dispensed temperature of 2-4°C above this has been found to be sufficient to allow for warming a bottle and feed formula therein to achieve an optimum final temperature.

In presently preferred arrangements the pump speed is altered to compensate for variability in the performance of the heat exchanger 12. The power of the heater is varied, as a consequence, to maintain boiling under all

circumstances. The performance of the heat exchanger is strongly affected by the inlet water temperature. With very cold inlet water (say 10°C) the temperature difference across the heat exchanger for a nominal outlet temperature of 40°C is of course 30°C. With warm inlet water however, which could be for example at 30°C, the temperature difference is only 10°C. Since the heat energy transferred across the heat exchanger is proportional to the temperature drop, a change from 10 to 30 represents a potential 300% increase. To compensate for this, the flow rate can be increased or decreased to maintain a fixed 40°C outlet temperature. The effect of this is that the corresponding outlet power required from the heating element can vary from 200 W to 2000 W.

Once a user signals that dispensing is to be stopped (or once a

predetermined volume has been dispensed), the heater and pump are switched off and the divert valve 32 is altered to close the outlet 34 and direct the remaining water back into the reservoir 2 by means of the drain tube 36. Although not shown a small bleed-back drain from the heating chamber to the reservoir may be provided. In this way, the entire system can be drained.

A second embodiment of the invention is shown in Fig. 7. In this

embodiment the cold water reservoir 2 and heat exchanger 12 are similar to those of the first embodiment. Again the reservoir 2 may be provided with a filter cartridge such as one of the Applicant's Aqua Optima (registered trade mark) water cartridges. However in this embodiment the heating chamber 72 differs in that there is an additional ventilation tube 74 projecting through the underside thereof. The tube opens near the top of the chamber 72 and extends down to a dual valve arrangement 76 in the lower part of the appliance.

As Fig. 7 shows, in this embodiment the tube 78 leading to the dispensing nozzle 80 rises up to a level H-i before curving back down to the nozzle 80. The effect of this is that a head of water H ₂ is required in order for water to be dispensed through the nozzle. The difference between H-i and H ₂ is accounted for by pressure losses through the heat exchanger 12 and associated conduits.

The heat exchanger outlet 30 is connected to the outlet tube 78 via a three- way T valve 82. The third port of the valve is connected to a drain path 84 back to the reservoir 2 by means of the dual valve arrangement 76. The dual valve arrangement 76 is such that the valve controlling the heating chamber ventilation tube 74 and that controlling the drain path 84 are interconnected. This may be seen more clearly in Figs. 8a - 8d. Fig. 8a shows schematically the body 86 of the valve arrangement with two separate bores 88, 90 for receiving the heating chamber ventilation tube 74 and the drain-back tube 84 respectively. Fig 8a also shows the valve piston 92 which is illustrated removed from its bore 94 for clarity.

The valve piston 92 comprises a shaft 96 and two enlarged diameter piston sections 98, 100. At one end of the shaft 96 is an actuating connector 102 to which a suitable actuator such as a solenoid (not shown) can be attached for moving the piston 92 along the bore 94 in use. As illustrated in Figs. 8b to 8d, there are three possible positions of the valve piston. In the first position shown in Fig. 8b, the valve piston is at its leftmost position in which the right piston section 100 is blocking the right bore 90 but the left bore 88 remains open. This means that the drain path tube 84 is closed, but the heating chamber ventilation tube 74 is open.

In the second position shown in Fig. 8c, the piston has been moved rightward so that the left piston section 98 now closes the left bore 88. However the right bore 90 also remains closed by the right piston section 100. Thus in this position the drain path tube 84 and the heating chamber ventilation tube 74 are both closed.

In the third position shown in Fig. 8d, the piston has been moved fully rightward so that the left piston section 98 still blocks the left bore 88 so closing it, but the right piston section 100 is no longer aligned with the right bore 90 and that is now opened. Thus in this position the drain path tube 84 is open but the heating chamber ventilation tube 74 is closed.

Operation of the embodiment shown in Figs. 7 and 8a-d will now be described. Upon initial commencement of operation the apparatus is sterilised, as previously explained, by boiling a small quantity of water in the heating chamber 72 generating steam. In this phase the valve arrangement is in the position shown in Fig. 8d, meaning that the ventilation tube 74 is closed, which forces the steam through the heat exchanger 12 and associated tubing. However the outlet drain tube 84 is open so that any initial condensate which forms, and which will run down to it by virtue of the layout of the apparatus, can be drained back into the reservoir 2. A user may place a baby's bottle beneath (or partly over) the outlet nozzle 80 so that the escaping steam can sterilise the bottle and the milk powder inside it. Any condensate forming on the rising part of the outlet tube 78 will also drain back down, against the flow of steam, through the drain tube 84.

Once the bulk of liquid in the heat exchanger 12 has been flushed out by steam and the system sterilised, the valve arrangement 76 is moved to the mid position shown in Fig. 8c. By thus closing the drain outlet more steam is forced into the bottle beneath the nozzle 80 so ensuring it and the milk powder are fully sterile. A short time later the valve 76 is moved to the position shown in Fig. 8b and the pump in the reservoir operated to continue with dispensing in the same way as in the first embodiment. Since the heating chamber ventilation tube 74 is open at this point the pump does not have to work against any pressure in the heating chamber 72. The layout of this embodiment means that no artificial water level control is necessary; as the boiling water leaves the heating chamber 72 it will begin to flood the heat exchanger 12 and to fill the outlet riser tube 78. Once the water level reaches level H ₂ in the hot inlet of the heat exchanger it reaches level H-i at the top of the outlet riser and so begins to flow out of the nozzle.

It will be appreciated by those skilled in the art that the embodiments described above are merely examples of how the principles of the invention can be employed and there are many possible variants within the scope of the invention. For example, the principles of the invention could be used to produce water or other liquid at a different temperature and for a different purpose than the preparation of baby feed. Moreover, the particular type of heater shown is not essential and any other flow heater or batch heater could be used instead.

In a different embodiment, the user selects an amount of warm water to be dispensed. Sterilisation is carried out not by steam but by water heated to approximately 70°C. During the sterilisation phase the outlet valve is closed to allow the water to circulate. A bypass path might be provided to bypass the cold water reservoir. The flow rate of the pump and/or the power of the heater may be controlled to maintain the required water temperature.

At the end of the sterilisation phase, a small volume of the hot water is dispensed - e.g. 10% of the volume requested by the user. This is sufficient to sterilise the milk powder if it has not been kept in sterile conditions. Thereafter ordinary dispensing is commenced at a lower temperature than is ultimately required. For example if the remaining 90% of the water is dispensed at approximately 37°C, the overall temperature will average approximately 40°C.