WO2011070365A1

WO2011070365A1 - Steam generating appliances

Info

Publication number: WO2011070365A1
Application number: PCT/GB2010/052061
Authority: WO
Inventors: Marc Gibson Collinson; Nicholas Edward Gibbs; Steven Anthony Ashton
Original assignee: Strix Limited
Priority date: 2009-12-09
Filing date: 2010-12-09
Publication date: 2011-06-16
Also published as: GB0921558D0; GB2476066A

Abstract

A steam generating appliance (1) comprises a water boiler (28) comprising a water inlet, an electrically heated evaporation chamber and a steam outlet (36). A pump (26) is arranged to deliver water to the inlet of the boiler (28) on demand. A steam delivery nozzle (32) is connected to the steam outlet (36) of the boiler (28). The steam delivery nozzle (32) extends down from a head portion (6) of the appliance (1). The head portion (6) and steam delivery nozzle (32) may be manually moveable up and down between a range of vertical positions relative to a base portion (2). Vertical movement of the head portion (6) and the steam nozzle (32) may be enabled by a linear actuator (42) provided in the stem (4) of the appliance (1).

Description

Steam Generating Appliances The present invention relates to steam generating appliances for domestic use, in particular to appliances for heating milk and other liquids or foodstuffs using steam.

Steam nozzles for heating and frothing milk are often provided on the side of espresso coffee machines and other beverage making appliances. Hot frothy milk is used to make coffee drinks such as cappuccino and other beverages such as hot chocolate. In these machines steam is typically delivered to the nozzle from the water heating unit which also supplies the heated water used to make beverages. A dedicated delivery pipe capable of withstanding pressurised steam may be needed to supply the steam nozzle.

Even in a small domestic appliance the water heating unit will typically hold a sufficient volume to make several cups of beverage. A drawback to steam generation in such beverage machines is that the whole volume of water contained in the hot water reservoir must be boiled to create steam. Hence there may be a substantial time delay before steam is available from a boiler filled with water.

Often when steam is required a user must wait for a water boiling indicator before activating the steam nozzle. Otherwise a mixture of hot water and steam will be delivered instead.

Steam generating appliances are available that do not heat a bulk volume of water to create steam. Such appliances typically pump water continuously through a flow heater comprising a heated pipe or a duct in a thermo block. However, flow heaters take time to heat up to a temperature high enough to evaporate water as it passes through the flow heater pipe or duct. Thermo blocks typically have a high thermal capacity resulting in a long heating up time. It is therefore necessary to switch on the flow heater and wait for a period of time before starting to pump water through to the steam nozzle, otherwise hot water will initially be ejected from the nozzle. A user display may be provided to indicate when the heater has reached its operating temperature. US 6,561 ,079 proposes a milk frothing device that uses a continuous flow heater with an intermediate tank disposed between the pump and the heater to accumulate water until the flow heater has reached its operating temperature necessary for steam generation, so that the pump and heater can be turned on simultaneously. However there is still a certain delay time after switch-on of the device before steam exits from the nozzle.

As well as suffering from delay times before steam generation is possible, conventional beverage making machines typically only provide a steam nozzle as an auxiliary component and the functionality of the nozzle is usually minimal. The barista making a beverage that requires frothed milk, such as a cappuccino, must employ skill and judgment in moving a container of milk up and down and around the steam nozzle so as to achieve thorough heating and a layer of foam on top of the milk.

It is important when making coffee beverages such as latte, macchiato and cappuccino to use a dense milk foam comprising micro-sized bubbles. To achieve a high quality milk foam there is needed a steam nozzle that can consistently deliver high temperature, pressurised steam vapour without any water content. It is also desirable for steam to be delivered readily on demand.

The present invention seeks to provide an improved steam generating appliance, e.g. for making frothed milk, and according to a first aspect the invention provides a steam generating appliance comprising: a water boiler comprising a water inlet, an electrically heated evaporation chamber and a steam outlet; a pump arranged to deliver water to the inlet of the boiler on demand; and a steam delivery nozzle connected to the steam outlet of the boiler.

Firstly it will be seen that in accordance with the invention water is only pumped to the boiler when there is a user demand for steam. Thus water is not heated needlessly and only the volume required to generate the desired amount of steam will be pumped to the boiler. This represents a considerable energy saving over appliances that generate steam by boiling a bulk volume of water or by heating a continuous flow of water so that steam is available when desired.

It will also be seen that in accordance with the invention there is provided a water boiler that only generates steam when water is supplied to it specifically for that purpose. As the chamber is initially heated dry, it can readily reach a high temperature when the boiler is turned on. Furthermore the boiler comprises an evaporation chamber arranged for the express purpose of heating and evaporating water to create steam. Accordingly steam may be generated more quickly in a water boiler according to the invention than it can, for example, in a hot water reservoir or flow pipe which already contains a volume of water and which is designed for bulk heating as well as steam generation. A water boiler comprising an evaporation chamber designed solely for the purpose of steam generation can provide several advantages over a continuous flow heater. It will be appreciated that water is pumped to the inlet of the boiler but preferably thereafter it is steam pressure in the evaporation chamber which pushes steam through the outlet and along the steam nozzle. Thus it is preferred that there is no pumped flow through the boiler, unlike a continuous flow heater. This means that water can not generally leave the boiler until it has evaporated, whereas in a continuous flow heater there is always a risk of some unevaporated water being pumped out with the steam.

The Applicant has appreciated that there is an advantage in allowing the boiler to generate steam on demand (i.e. when water is pumped to the boiler) but in its own time (i.e. without a forced flow through the boiler). As the evaporation chamber is heated and water is pumped therein, it will take a little time for the water first introduced to boil and evaporate and for the steam pressure to build up. Hence the output of steam from the nozzle is gentle to start with and then increases to a steady discharge rate. The slow build up of the steam discharge rate has been found to be desirable, especially when using the nozzle to heat liquids and foodstuffs, as it can avoid any surprising initial spurts of steam which may cause the foodstuff in contact with the nozzle to spray out. The user can adjust the depth of the nozzle in the foodstuff or liquid as the steam discharge increases to ensure there is no splashing. In contrast, a continuous flow heater is designed to produce a pressurised steam supply from the offset.

A further advantage of the invention is that steam can be generated continuously by the boiler for as long as water is pumped to the inlet. This allows the nozzle to be put to multiple uses. For example, to heat a cup of milk steam delivery may only be required for 20-30s whereas to heat a bowl of soup steam delivery may be required for a minute or more. It will be appreciated that such a continuous delivery of steam on demand is different to the steam delivery provided by cordless devices such as steam irons, where a relatively short burst of steam may be provided by a charge of water supplied to a boiler from a pressure accumulator chamber. Once the pressurised supply has been exhausted, however, it must be replenished before another burst of steam can be generated.

It will be understood that what is meant by a "steam delivery nozzle" in accordance with the invention is an outlet tube or spout for ejecting steam. The nozzle is designed to heat a liquid or foodstuff when submerged therein. The steam outlets in the sole plate of an iron, on the other hand, are not nozzles.

Although the nozzle may provide a diffuse steam delivery, preferably the nozzle is arranged to eject a jet of pressurised steam. Further preferably the nozzle is arranged to increase the steam velocity before it is discharged, for example using a throttling mechanism. One or more steam discharge outlets may be provided. Such a nozzle typically comprises a compression portion and an expansion portion, or at least a cross-sectional constriction, so as to speed the flow of steam as it is discharged from the outlet(s). The nozzle may be submerged for steam heating of liquid or foodstuffs, and may also be held at a liquid surface to obtain a three-phase boundary of air, steam and liquid which will aerate the liquid and form a foam.

According to the invention water is pumped to the inlet of the boiler on demand and then steam generated in the evaporation chamber is delivered to the steam nozzle. Unlike a continuous flow heater, water can not generally leave the boiler until it has evaporated. This may be aided by preferably arranging the water inlet at the bottom of the boiler and the steam outlet at the top of the boiler. Thus there is not the same adverse effect if the boiler is heated up at the same time as water is pumped to the inlet. There is not the same need to build in a delay time for the boiler to reach its operating temperature. In at least one set of embodiments it is preferable that the boiler and pump are arranged to be switched on

simultaneously in response to a user demand for steam. This provides for a very simple mode of operation, for example a user may need only to activate one switch to operate the steam nozzle and there is no need for a temperature regulator for the boiler and a "boiler ready" indicator or the like. Advantageously there is

substantially no time delay between a user demand for steam and the introduction of water into the boiler by the pump.

In another set of embodiments there may be provided means to delay the pumping of water to the boiler inlet until the boiler has reached a predetermined operating temperature. A temperature sensitive control means may be arranged to provide an electrical connection to the pump only when it is detected that the operating temperature has been reached. Alternatively a timer could be

programmed to delay the operation of the pump until such time that the boiler is expected to have heated up. It is preferred that the pump and the electric heating means of the boiler are connected electrically in parallel so that they may be controlled by a common on/off switch. This still provides the advantage of a simple "one button" operation of the appliance, while also ensuring that the boiler is hot enough when water is pumped into it that steam generation starts rapidly.

Advantageously the start-up time may be reduced.

Furthermore the boiler can preferably heat and evaporate water to generate steam without a substantial time delay as it provides a dedicated evaporation chamber. Steam may be delivered to the nozzle within around 45 seconds of water being pumped into the boiler, as opposed to the two minutes or more that is typical in a pressurised steam generator system. Rapid steam generation may be promoted by pre-heating the boiler to a predetermined operating temperature before water is pumped in. The boiler has several preferred features which can contribute to its improved steam generating performance, and these are described in more detail below.

Preferably the boiler comprises a water inlet, an electric heater, a steam outlet and an evaporation space bounded by at least one surface in thermal contact with the heater. Preferably the evaporation space is configured to present an expanding cross-sectional area in a direction away from the water inlet. This corresponds to an increasing internal volume in the evaporation space and a corresponding increase in surface area during the advancement, and a

corresponding rise in temperature, of the water and steam. In accordance with such arrangements, the evaporation space can start off relatively small to give good intimate contact between the water and the heated surface(s) of the evaporation space to give efficient evaporation of the water, whilst at the same time allowing the steam so generated to expand into the increasing volume as it flows away from the water inlet e.g. to the steam outlet.

In preferred embodiments the evaporation space has a constant, preferably shallow height. This can maximise the surface area over which the water is spread to enhance the efficiency of steam generation. Clearly when the height of the evaporation space is constant, an expanding cross-section may be provided by an increasing width to give an increase in the cross-sectional area of the evaporation space in a direction away from the water inlet. In some example embodiments, the evaporation surface is convex, concave or conical. Other substantially two or three dimensional forms such as fans, deltas, hemispheres, parabolas, prisms, pyramids and other suitable forms can be employed to provide the required increasing volume and surface area. Of course, other, more complex, shapes could be used to give the same effect, both internally to enhance surface area and so evaporation efficiency and externally to minimise the space required for the boiler in the appliance.

The heated surface bounding the evaporation space (hereinafter referred to as "the evaporation surface") is preferably non-planar. This facilitates maximising the surface area available in a given volume occupied by the boiler within the appliance. In a set of preferred embodiments, the surface area of the evaporation surface (measured prior to the application of any surface enhancing coating) is more than 1 .5 times the maximum planar projection of the surface (i.e. the footprint), more preferably greater than 1 .75 times, more preferably greater than twice.

Preferably the evaporation surface is hydrophilic. This might be a natural characteristic of the material used for the evaporation surface, it might be achieved or enhanced by a suitable surface treatment and/or it might be achieved or enhanced by a suitable heat resistant coating material.

In a set of preferred embodiments the boiler is configured to produce superheated steam. In some preferred embodiments the boiler has a temperature of between 100 and 500 ^QC, preferably between 105 and 380 ^QC, and more preferably between 200 and 280 ^QC. Preferably the internal steam pressure generated within the boiler should not be greater than that of the water pressure entering it, else water will be prevented from entering the device, resulting in a subsequent drop in steam flow rate and unwanted fluctuation in steam output.

Steam may simply be allowed to leave the boiler once it has passed through the evaporation space. However, in a set of preferred embodiments the boiler comprises means for collecting the steam. This allows it, for example, to be channelled into one or more steam outlet(s) for delivering it to the steam nozzle of the appliance. Preferably the means for collecting steam comprises means for trapping unevaporated droplets of water. For example this might be a protruding outlet tube encouraging steam channelled by the walls of the chamber to undergo a change of direction leading to expulsion of entrained droplets.

As the boiler is required to produce steam on demand it is beneficial, in order to minimise the initial delay between filling it with water and producing steam, that when it does not contain water, it is allowed to increase in temperature and therefore store thermal energy which can be used to heat the initial supply of water to boiling as rapidly as possible. In a set of preferred embodiments, the useable energy which the boiler is adapted to store, that is the amount of heat energy available to generate steam, is more than 20 kilojoules, more preferably greater than 35 kilojoules and more preferably greater than 50 kilojoules. The boiler may represent a relatively large thermal mass. It preferably comprises a die cast unit with a heating element preferably embedded in the cast body of the evaporation chamber.

The direct pumping of water into the boiler also means that steam delivery can be interrupted and resumed on demand. If the time interval between steam delivery cycles is relatively short, in comparison with the thermal storage capacity of the boiler, then the boiler may maintain a temperature sufficient to evaporate water even when it is first pumped into the boiler at the start of a new delivery cycle. The appliance may therefore provide for consistent steam delivery from one cycle of use to the next.

A boiler in accordance with the preferred features set out above is particularly beneficial where steam is required on demand, for example to rapidly heat a vessel of milk, since the features described above allow for the very rapid production of steam from when water first enters the water inlet as compared, for example, with a more traditional boiler unit in which a heating element is used to heat a body of water. An important factor in achieving this effect is to supply water to the boiler under pressure and thus in a particularly preferred set of embodiments the pump is arranged to supply pressurised water to the water inlet of the boiler.

The pressure of the water supply to the boiler is preferably greater than 0.5 bar, e.g. more than 1 bar, and might be up to 3 bar or more.

The pump is preferably arranged to provide water to the boiler at a steady rate. This simplifies the appliance and is particularly beneficial when there is provided a single switch to connect the electrical supply to both the pump and the heating element of the boiler. However the pump rate could be user variable, for example by providing an adjustable valve to throttle the flow of water to the boiler. This may be desirable where different rates of steam discharge are preferred e.g. for heating different foodstuffs.

The pump may be connected to an external water supply. However it is preferred that the appliance comprises its own water reservoir to supply the pump. The water reservoir should be designed to hold a sufficient volume of water to provide steam for several cycles of operation before it is necessary for it to be refilled. Although the water reservoir may be provided anywhere in the appliance, in a preferred set of embodiments the water reservoir comprises a tank provided in the base of the appliance. This can advantageously add to the stability of the appliance, for example on a counter-top in a domestic setting. Means are provided to access the reservoir for refilling. A water level gauge and/or refill indicator may be provided.

Advantageously the appliance can be used to generate steam and heat many different kinds and amounts of liquid or foodstuffs. In order to allow the steam nozzle to access a large range of vessel sizes and shapes it preferably extends down freely from a head portion of the appliance. The head portion may be connected to a base portion of the appliance by a stem. Apart from the stem, there is preferably free space all around the nozzle to allow for access. This is an improvement over steam nozzle attachments that are often provided on the side of a beverage machine as an auxiliary component and that are only accessible e.g. by relatively small cylindrical vessels such as milk jugs.

Furthermore such fixed nozzle attachments require a user to hold the vessel up to the nozzle so that it is immersed into the liquid to be steam-heated. The user's hand is close to the steam discharge end of the nozzle and may get burnt. There is a danger that the user may drop the vessel or spill some of its contents, for example due to the force of steam being injected, or that the user may be splashed by hot liquid. In order to overcome these problems it is therefore preferred that the appliance comprises a base portion arranged to receive a vessel in use. The vessel may contain any liquid or foodstuff to be injected with steam. The vessel can rest safely on the base portion while the steam nozzle is being used and the user does not have to hold the vessel. Hence there is less risk of the user being scalded by steam from the nozzle or hot substances splashed out of the vessel. Of course a user can hold or move the vessel while operating the steam nozzle if desired.

Preferably the base portion, or at least the vessel receiving part of the base, is located substantially below the steam nozzle at least during use. The steam nozzle may be connected to a part of the head portion that is tiltable or rotatable so as to enable the nozzle to be swung out of the way when a vessel is placed down on the base.

The Applicant has appreciated that when a base portion is provided to receive a vessel of liquid to be heated, there may be a problem when different vessel sizes and/or different liquid levels are used. If there is a fixed distance between the discharge end of the steam nozzle and the base portion, in use, then the nozzle will not penetrate to the same depth in all vessels. The nozzle may not always reach into the liquid to be heated. It is therefore preferred that the steam nozzle is moveable between a range of vertical positions. Although the steam nozzle itself may be made extendable and retractable, it is preferred that the steam nozzle has a fixed length and that the head portion of the appliance is moveable relative to the base portion so as to change the vertical height of the steam nozzle above the base.

Vertical movement of the head portion relative to the base portion could be achieved in many different ways. For example, the head portion could be hingedly connected to a stem extending from the base portion. But it is preferred that the head portion is fixed in a horizontal position, aligned above the base portion, so that the nozzle is always pointing down in use. The head portion is preferably connected to the base portion by a linear actuator arranged to effect movement of the head portion relative to the base portion. The linear actuator may be provided in a vertically extendable and retractable stem. The head and base portions then stay in alignment with the stem providing for changes in their relative vertical separation. Movement of the head portion may be achieved by any suitable means, for example using a sliding guide with friction fit, a hydraulic arm, a screw spindle, a linear motor, etc. as a linear actuator.

Movement of the linear actuator, and hence movement of the head and steam nozzle, may be automated. However it is preferred that the head is manually movable, and thus the height of the steam nozzle manually adjustable, for ease of use. A user may therefore position a vessel with contents to be heated on the base portion below the steam nozzle, and then manually move the head portion down until the steam nozzle is at the desired height in the vessel. To assist in vertical positioning the stem may be provided with means to lock the head at a particular vertical height. The could help to ensure that the steam nozzle is fixed at a height so as to stay immersed in the contents of a vessel while steam is being generated.

The Applicant has appreciated that users will often wish to move the steam nozzle up and down in a vessel while steam is being generated, to help heat the liquid or foodstuff evenly and as quickly as possible. It is therefore preferred that the head portion is free to move during use, although lock means may also be provided. When a user has finished heating the contents of a vessel, it is desirable to move the steam nozzle up out of the way so that the vessel can be removed from the base portion without needing to tip it sideways and risk spilling its contents. To make this easier the head portion is preferably biased to move up relative to the base portion to its maximum vertical displacement. Thus in the absence of a user- applied force pushing the head down, the head will automatically return to its raised position and the base portion will be accessible for vessels to be removed and replaced.

This is considered novel and inventive in its own right, and thus when viewed from a further aspect the invention provides a steam generating appliance comprising a base portion, a head portion comprising a steam delivery nozzle extending down towards the base portion, and a linear actuator arranged to effect movement of the head portion relative to the base portion, wherein the linear actuator is biased to move the head portion to a position of maximum displacement from the base portion.

According to this aspect of the invention the head portion and steam nozzle will automatically be moved away from the base portion when there is no force applied to the linear actuator to overcome the bias force. As mentioned above, it is preferable for the linear actuator to be manually movable against the bias force so as to allow a user flexibility in moving the steam nozzle to and away from the base portion. Controlled movement of the steam nozzle is facilitated by the biased actuator as it means that a user only has to apply and release a force in one direction. If the linear actuator were not biased then a user would have to pull the head up to move it away from the base. This may not be easy when the head portion includes the weight of the steam nozzle and potentially also the weight of the boiler. This feature is therefore particularly preferred where the boiler is provided in the head portion of the appliance.

This further aspect of the invention may find use in all kinds of steam generating appliances comprising a steam delivery nozzle, and not just those having a boiler of the type described above with respect to the first aspect of the invention. However the other preferred features described above are generally applicable to an appliance according to both aspects of the invention.

The linear actuator is preferably biased by a spring. In order to ensure smooth movement of the head portion, movement of the linear actuator is preferably damped. The damping may be arranged to provide a delay in the biased movement of the head when a counter force is removed, so that the head does not move suddenly and the steam nozzle does not come up out the liquid it is heating while steam is still being released. This can help to prevent liquid from being accidentally sprayed out of the vessel if the head is accidentally released during steam delivery.

The steam nozzle can take any suitable form. Steam nozzles are known that comprise both steam outlets and air inlets so that liquid is both heated and frothed. The steam discharge means of the nozzle is preferably arranged to minimise the noise produced by the nozzle. At least according to preferred embodiments the boiler delivers pressurised steam to the nozzle and the steam velocity is increased in the nozzle. This is different to the atmospheric venting of steam that takes place at the sole plate of a steam iron. For ease of cleaning, it is preferred that the steam nozzle is removable. A steam pipe may connect the steam outlet(s) of the boiler to the steam nozzle.

The invention also extends to a domestic steam generating appliance comprising: a water boiler comprising a water inlet, an electrically heated

evaporation chamber and a steam outlet; a pump arranged to deliver water to the inlet of the boiler on demand; and a steam delivery nozzle connected to the steam outlet to discharge one or more pressurised jets of steam for heating liquids or foodstuffs.

A preferred embodiment of the present invention will now be described, by way of example only, and with reference to the accompanying Figures, in which:

Figure 1 a is a perspective view of a steam wand appliance according to the preferred embodiment;

Figure 1 b in a perspective view of the steam wand appliance according to the preferred embodiment with a cup of liquid to be heated in position below the nozzle;

Figure 2 is another perspective of the steam wand appliance according to the preferred embodiment with the drip tray removed;

Figure 3 is a cross-sectional side view of the steam wand appliance according to the preferred embodiment with the steam nozzle in a raised position;

Figure 4 is a cross-sectional side view of the steam wand appliance according to the preferred embodiment with the steam nozzle in a lowered position; and

Figure 5 is an schematic circuit diagram showing some of the main electrical components of the appliance.

There is shown in Figures 1 -4 a steam wand appliance 1 generally comprising a base portion 2, a retractable stem 4 and a head portion 6. The base portion 2 rests on a counter-top and receives a vessel 8 in use, as is shown in Figure 1 b. The vessel 8 is placed on a drip tray 10. Apertures 12 in the drip tray 10 allow any spilled liquid to drain into a cavity below. The drip tray 10 is removable.

Figure 2 shows the appliance with the drip tray 10 removed from the base 2. It can be seen that a water reservoir tank 14 is accommodated in the base 2, beneath the drip tray 10. An inlet to the tank 14 is fitted with a sealing cap 16. The drip tray 10 can be removed to allow access to the cap 16 when it is desired to refill the tank 14. The drip tray 10 is then placed back over the tank 14 so as to cover and protect the cap 16. Of course, the fill cap 16 does not necessarily have to be located below the drip tray 10 and could instead be accessible e.g. on a side of the base 2.

A water pipe (not shown) is connected to an outlet from the reservoir tank 14 and exits the base portion 2 through an opening 18 seen in Figure 1 . The water pipe runs on the outside of the appliance 1 and enters the head portion 6 via a pipe section 20 also seen in Figure 1 . The water pipe may be made of a plastics material and stiffened with steel wire so as to form a "lazy loop" between the opening 18 and the end section 20, in the form of an umbilical cord. Sufficient length of pipe is provided to account for movement of the head 6 relative to the base 2. The water pipe is preferably run on the outside of the stem 4 so as not to interfere with the movement mechanism inside the stem (described below).

However it may instead be accommodated inside the stem 4.

A mains electrical lead (not shown) may be threaded through a guide 22 formed on the side of the stem 4 near the base 2. This helps to ensure that the flex runs from a mains socket to the appliance 1 at counter-top level. The lead then runs from the guide 22 up the side of the stem 4 and enters the head portion 6 through an opening 24 seen in Figure 1 . Thus it will be appreciated that all of the electrically-powered components of the appliance are conveniently located together in the head portion 6, where they are safe from leakage from the drip tray 10 or water tank 14.

As can be seen from the cross-sectional view in Figures 3 and 4, the head portion 6 comprises an electric pump 26, an electrically heated boiler unit 28, a steam delivery pipe 30 and a steam discharge nozzle 32. The pump 26 is connected to the water tank 14 via the water pipe and supplies water to the boiler 28. Both the pump 26 and the boiler 28 are connected to the electrical supply provided by the flex entering the head 6 through the opening 24. For simplicity the electrical and water connections between the pump 26 and the boiler 28 are not shown.

A demineralising filter may be provided between the water tank 14 and the pump 26, for example in the base 2 at the connection between the water tank and the water pipe. The filter may comprise a sodium-, potassium- or hydrogen-based ion exchange resin. This can prevent scale build-up in the boiler 28.

Although the boiler 28 is not shown in detail, it generally comprises a die- cast metal unit comprising upper and lower body members clamped together with a heat-resistant seal therebetween. Inside the boiler 28, the lower body member defines a conical evaporation chamber. An electrical heating element is embedded into the lower body member of the boiler 28 during manufacture. The embedded element is helically arranged so that it wraps around the conical evaporation chamber formed by the boiler body. The ensures an even heat distribution.

A temperature regulator 34 is provided in thermal contact with the side of the boiler 28. The temperature regulator 34 may be a bimetallic actuator. The regulator 34 forms part of a thermally sensitive control for the electrical supply to the pump 26. Only when the regulator 34 senses that the boiler 28 has reached a predetermined minimum operating temperature, for example 120-160 °C, does it operate to connect power to the pump 26. This ensures that the boiler 28 has already started to heat up when water is pumped into it, so that evaporation and steam generation starts to take place straightaway. This avoids long start-up times when the appliance is first switched on, and helps to ensure that there are no unevaporated water droplets in the discharged steam.

Although not shown, one or more indicator lights of other form of indication might be provided to a user to indicate that the boiler 28 has reached its predetermined temperature. In other embodiments the temperature regulator 34 may be omitted but if water is pumped to the cold boiler straightaway then it will take longer to heat up and generate steam. A timer delay system may be used instead.

The boiler 28 is provided with a water inlet (not shown) which fluidly communicates with the lowest point of the conical evaporation chamber. A steam outlet 36 is fluidly connected with the top of the evaporation chamber. The steam outlet 36 is connected to the steam delivery pipe 30, which passes down past the boiler 28 and exits through the bottom of the head 6. The steam delivery pipe 30 extends down below the head 6 and is terminated by the steam nozzle 32. The steam nozzle 32 is removably attached to a lower end of the steam pipe 30. A connector 38 is provided with a lever to turn and loosen the connector 38 when it is desired to remove the nozzle 32 for cleaning, and then to turn and tighten the connector 38 when the nozzle 32 is replaced. Once the steam nozzle 32 is fixed in position it cannot move relative to the head portion 6.

Vertical movement of the head portion 6 and thus of the steam nozzle 32 is enabled by a linear actuator 42 provided in the stem 4 of the appliance. It can be seen from Figures 3 and 4 that the stem 4 is made up of a lower section 4a and an upper section 4b that telescopes inside the lower section 4a. The upper section 4b is fixedly connected to the head portion 6 while the lower section 4a is fixedly connected to the base portion 2. The linear actuator 42 in the stem 4 comprises a movable cylinder 44 attached in the upper section 4b of the stem and a fixed rod 46 attached in the lower section 4a of the stem. The cylinder 44 is slidably mounted on the rod 46 and connected thereto by a helical spring 48.

In the absence of any user-applied force, the spring 48 biases the cylinder 44 and the upper section 4b of the stem to an uppermost position. The stem 4 is shown in such an extended position in Figure 3. In order to retract the stem 4, as is shown in Figure 4, a user presses down on the head 6 to push the upper stem section 4b and its cylinder 44 down against the spring 48 so that the rod 46 slides inside the cylinder 44. As soon as the pressure on the head 6 is released, the spring 48 will push the cylinder 44 and upper stem section 4b back up to a raised position. The spring force is chosen so as to provide for a slow, damped motion.

When the power lead is connected to the mains electrical supply, electrical power is supplied to the heating element of the boiler 28. This means that the boiler 28 starts to heat up as soon as the appliance 1 is plugged in and turned on at the wall. This is advantageous as it means that the boiler 28 is likely to have already reached the minimum operating temperature required by the regulator 34 by the time a user is ready to use the appliance. In this situation water could be pumped to the boiler 28 as soon as there is a user demand for steam. A power on/off switch may be provided, however, where desired.

A steam button 40 is provided on the head portion 6. The button 40 is arranged to act on a momentary switch which connects the electrical supply to the pump 26 whenever it is pressed and held down. The pump 26 and boiler 28 are arranged electrically in parallel so that they are energised simultaneously, or at least once the temperature regulator 34 allows the connection to the pump 26 to be completed. Thus a user only has to press and hold one button 40 for water to be pumped up to the heated boiler 28 and for steam to be generated. Once the user releases the button 40 the pump 26 ceases operation and steam generation is over as soon as the water left in the boiler 28 evaporates. Steam discharge will therefore halt within only a few seconds. Of course, the momentary switch could be replaced with a regular switch so that instead a user presses the button 40 once to start the pump 26 and then presses the button 40 once again to stop the pump 26.

The circuit diagram of Figure 5 shows schematically how the heating element of the boiler 28 and the pump 26 may be electrically connected in parallel to the mains power supply V. S1 represents the main on/off switch and this could either be the on/off switch at the wall socket or a dedicated switch on the appliance. S2 represents the momentary action switch which is operated by the steam button 40 described above. An advantage of the momentary switch S2 is that the pump 26 cannot be left on if the appliance is left unattended.

Whereas both S1 and S2 are user-operated switches, S3, S4 and S5 are switches internal to the appliance. S3 represents a switch that is controlled by the temperature regulator 34. This switch S3 is open until the boiler 28 reaches a predetermined minimum temperature, e.g. in the range 120-160 °C. Once the boiler 28 has reached the predetermined temperature the switch S3 remains closed. S4 represents a switch that is controlled by a thermostatic control T1 for the boiler 28. The thermostatic control T1 responds to the temperature of the boiler 28 and disconnects the power supply if the boiler 28 starts to overheat beyond its normal operating range, e.g. 180-240 °C. The thermostatic switch S4 is normally closed, but may cycle on/off to maintain the boiler 28 within the desired temperature range. S5 represents a switch controlled by a thermal fuse T2. The thermal fuse T2 is designed to rupture and open the switch S5 only in the event of a serious overheat condition, for example due to a fault in the thermostat T1 , and therefore provides a safety back-up. Thus in normal operation switches S1 , S3, S4 and S5 will all be closed and it is only the momentary switch S2 that is opened and closed depending on user operation of the steam button 40.

Operation of the steam wand appliance will now be described with reference to the Figures. As soon as the power lead of appliance 1 is connected to the mains power supply, switch S1 is closed and power is supplied to the heating element of the boiler 28. The boiler 28 will start to heat up relatively quickly as it will be dry. The reservoir tank 14 should contain water before operation is commenced. A fill level gauge may be provided for a user to check the volume of water left in the tank 14. An indicator light or the like may also be provided to alert a user when the tank 14 needs to refilled. Once the tank 14 has been filled and the drip tray 10 replaced, a vessel 8 containing a liquid or foodstuff to be heated is placed on the base 2 on top of the drip tray 10 and beneath the steam nozzle 32, as is shown in Figure 1 b. For example it may be desired to heat and froth a mug of milk to make a coffee beverage or hot chocolate drink.

When the appliance 1 is in its rest position (Figure 3) the head 6 is raised to its maximum height from the base 2 and there is therefore plenty of space beneath the steam nozzle 32 to allow a user to place a vessel down on the base 2. The vessel could have many different sizes and shapes. When the user is ready to heat the contents of the vessel, he or she presses down on the head portion 6 of the appliance to push the steam nozzle 32 down into the liquid or other foodstuff in the vessel. The upper stem portion 4b telescopes into the lower stem portion 4a until the head 6 reaches the desired height.

Once the nozzle 32 is in position, the user presses the steam button 40 to connect the pump 26 electrically in parallel with the boiler 28 to the power supply. If the boiler 28 has not yet heated up enough then the temperature regulator 34 will sense that the boiler 28 has not reached its minimum operating temperature and switch S3 will be open. An indicator light (not shown) may warn the user that the boiler 28 is still heating up. Once the boiler 28 is hot enough, the temperature regulator 34 will close the switch S3 and complete the electrical connection to be made to the pump 26. As soon as the pump 26 is activated it starts to pump water out of the tank 14, up through the water pipe (not shown), through the pump 26 in the head 6 and into the water inlet of the boiler 28. A pump rate of around 37 g/min may be used.

As the button 40 is positioned on top of the head portion 6, it is convenient for a user to press the button 40 while also pushing down on the head 6 with the same hand. Single-handed operation is therefore provided. The user may use his or her other hand to hold the vessel and swirl it during the heating process if desired. As steam will not be discharged from the nozzle 32 straightaway, the user may press the button 40 at the same time as pushing the head 6 down to the desired height. The boiler 28 will start to fill with water while the user is positioning the nozzle 32. The boiler inlet may pass through the heated die cast body of the boiler 28 and thus water will be preheated so that when it enters the evaporation chamber its temperature is raised significantly above ambient (but below boiling). The water enters the bottom of the conical chamber. The cross sectional area of the evaporation space increases in a direction away from the inlet as the water travels up the cone. This increasing volume allows for expansion of the steam created during the evaporation process and so limits the tendency for a build up in pressure to reduce the inflow rate of water. The pressure of the steam produced in the evaporation chamber forces it out of the steam outlet 36 and down the steam discharge pipe 30. The outlet pipe 36 may project slightly into the evaporation chamber to help trap any small droplets of water entrained in the steam so that these fall back into the boiler to be evaporated. The steam exiting the boiler 28 is superheated.

For as long as a user presses down the steam button 40 there is a steady flow of water into the boiler 28 to continuously generate steam which is discharged through the nozzle 32. If a user releases the steam button 40 to check the temperature of the liquid or foodstuff being heated then the discharge steam ceases within a few seconds. He or she can release pressure on the head 6 to allow it to rise up so the nozzle 32 is lifted out of the vessel. If it desired to continue heating the contents of the vessel then the head 6 is simply pressed down again while also pressing the steam button 40 to energise the pump 26. As the boiler will already be hot, steam will be generated again quite quickly. The die cast boiler 28 has a high thermal capacity which allows a significant amount of thermal energy to be stored as a result of the high operating temperatures (typically 200-280 °C).

Once the user has finished using the steam nozzle 32, the head 6 is released completely. Due to the bias of the spring 48 on the cylinder 44 in the linear actuator 42 mechanism, the upper part 4b of the stem 4 telescopes up out of the lower part 4a until it reaches its maximum height. The spring force is selected to damp this motion so that the head 6 moves up slowly rather than jolting. Once the head 6 is raised up the vessel can be lifted from the base 2.

The steam nozzle 32 can be removed from the steam pipe 30 by turning a lever to loosen the connector 38. The steam nozzle 32 can be washed, by hand or in a dishwasher, and then replaced on the steam pipe 30. The connector 38 is turned to tighten its grip on the nozzle 32. As the water tank 14 is provided in the base 2, it does not contribute to the weight of the movable head 6 and can be made relatively large. Certainly it can be designed to hold a sufficient volume of water to generate several minutes worth of steam. The appliance may therefore be used several times over before it is necessary to replenish the tank 14. The weight of the water tank 14 can in fact help to stabilise the base 2.

It will be apparent that various changes in the form of the preferred embodiment described above may be made within the scope of the invention. For example, although not shown as part of this embodiment, means may be provided for a user to regulate the rate at which steam is generated, for example by operating a valve to throttle the flow rate of water into the boiler. Additionally or alternatively it may also be possible for a user to vary the pump rate.

Claims

1 . A steam generating appliance comprising:

a water boiler comprising a water inlet, an electrically heated evaporation chamber and a steam outlet;

a pump arranged to deliver water to the inlet of the boiler on demand; and a steam delivery nozzle connected to the steam outlet of the boiler.

2. A steam generating appliance as claimed in claim 1 , wherein the steam delivery nozzle is moveable between a range of vertical positions.

3. A steam generating appliance as claimed in claim 1 or 2, wherein the steam delivery nozzle is manually moveable.

4. A steam generating appliance as claimed in claim 1 , 2 or 3, comprising a head portion providing the steam delivery nozzle and a base portion arranged to receive a vessel in use.

5. A steam generating appliance as claimed in claim 4, wherein the base portion, or at least the vessel receiving part of the base portion, is located substantially below the steam delivery nozzle at least during use.

6. A steam generating appliance as claimed in claim 4 or 5, wherein the head portion of the appliance and the steam delivery nozzle extending therefrom are moveable together relative to the base portion.

7. A steam generating appliance as claimed in claim 4, 5 or 6, wherein the head portion is manually moveable to move the steam delivery nozzle between a range of vertical positions.

8. A steam generating appliance as claimed in any of claims 4 to 7, wherein the head portion is connected to the base portion by a linear actuator arranged to effect movement of the head portion up and down relative to the base portion.

9. A steam generating appliance as claimed in any of claims 4 to 8, wherein the head portion is biased to move up relative to the base portion to provide a maximum vertical displacement for the steam delivery nozzle.

10. A steam generating appliance comprising a base portion, a head portion comprising a steam delivery nozzle extending down towards the base portion, and a linear actuator arranged to effect movement of the head portion relative to the base portion, wherein the linear actuator is biased to move the head portion and steam delivery nozzle to a position of maximum displacement from the base portion.

1 1 . A steam generating appliance as claimed in claim 8, 9 or 10, wherein the linear actuator is provided in a vertically extendable and retractable stem.

12. A steam generating appliance as claimed in any of claims 4 to 1 1 , wherein a or the boiler is provided in the head portion of the appliance.

13. A steam generating appliance as claimed in any of claims 1 to 9, wherein the boiler and pump are arranged to be switched on simultaneously in response to a user demand for steam.

14. A steam generating appliance as claimed in claim 13, wherein there is provided means to delay the delivery of water to the boiler by the pump until the boiler has reached a predetermined operating temperature.

15. A steam generating appliance as claimed in any preceding claim, wherein a or the boiler is arranged to deliver pressurised steam to the steam delivery nozzle.

16. A steam generating appliance as claimed in any preceding claim, wherein a or the water inlet to a or the boiler is arranged at the bottom of the boiler and a or the steam outlet is arranged at the top of the boiler.

17. A steam generating appliance as claimed in any preceding claim, wherein a or the boiler comprises an evaporation space bounded by at least one evaporation surface in thermal contact with an or the electrical heater.

18. A steam generating appliance as claimed in claim 17, wherein the evaporation space is configured to present an expanding cross-sectional area in a direction away from a or the water inlet.

19. A steam generating appliance as claimed in claim 17 or 18, wherein the evaporation surface of the boiler is convex, concave or conical.

20. A steam generating appliance as claimed in claim 17, 18 or 19, wherein the evaporation surface of the boiler is hydrophilic

21 . A steam generating appliance as claimed in any preceding claim, wherein a or the boiler comprises a die cast unit with a heating element embedded in the cast body of its evaporation chamber.

22. A steam generating appliance as claimed in any preceding claim, wherein a or the pump is arranged to supply pressurised water to a or the water inlet of a or the boiler, preferably at a pressure greater than 0.5 bar, more preferably greater than 1 bar, and preferably up to 3 bar or more.

23. A steam generating appliance as claimed in any preceding claim, comprising a water reservoir to supply a or the pump.

24. A steam generating appliance as claimed in any preceding claim, wherein the nozzle is arranged to increase the steam velocity before steam is discharged from one or more outlets.

25. A steam generating appliance as claimed in any preceding claim for domestic use, wherein the steam delivery nozzle is arranged to discharge one or more pressurised jets of steam for heating liquids or foodstuffs.