FIELD OF INVENTION

The present invention relates to boilers for use in apparatuses for steaming animal fodder, in particular hay steamers, and to apparatuses for steaming animal fodder.

BACKGROUND

Hay, and other types of fodder such as straw, silage and haylage, are commonly fed to horses, as well as other livestock, and may be used for growing plants, fruit and vegetables such as mushrooms. However, such fodder may contain many different types of bacteria, mould spores and dust particles that can affect a horse’s breathing and cause coughing. The particles are respiratory irritants, and can lead to respiratory diseases such as chronic obstructive pulmonary disease (COPD).

Some of these disadvantages may be overcome by using a hay steamer to treat hay bales with steam.

An example of a hay steamer is to be found in patent publication GB 2,338,167. The body of the hay steamer comprises four side walls that rise from a base to form a chamber into which hay bales may be loaded. The top of the steamer comprises a hinged lid that may be opened to allow loading and unloading of hay bales, and closed to form a closed chamber when the hay bales are being steamed. A separate boiler unit heats water to produce steam. The boiler unit is connected to the body of the hay steamer via a hose which, in turn, connects to a pipe that extends along the bottom of the chamber. This pipe is provided with apertures that allow steam to enter the chamber and steam the hay bale. The boiler unit contains a large water tank which is heated by an electrical heating element to generate the steam which then passes down the hose to the body of the hay steamer.

SUMMARY

In a first aspect, there is provided a boiler unit comprising a heater chamber housing a heater element. The heater element is configured to heat water retained within the heater chamber to generate steam. The boiler unit further comprises a pair of separated electrodes located within the heater chamber. The boiler unit is configured to measure an electrical value corresponding to either the resistance between the pair of separated electrodes or another electrical value that is proportionate to the resistance between the pair of separated electrodes. In addition to the resistance between the electrodes, the electrical value may be the conductivity between the electrodes or the current flowing between the electrodes. The boiler unit is also configured to determine whether the water level in the heater chamber relative to the pair of separated electrodes is too low using the measured electrical value.

The boiler unit may be suitable to all types of steam generation apparatus, such as, but not limited to, apparatus for steaming animal fodder, for example hay steamers. Accordingly, there is also provided an apparatus for steaming animal fodder, such as a hay steamer, including any of the boiler units described herein.

The reason for determining the water level within the heater chamber is to avoid the heater chamber running dry whilst the heater element is switched on. As water is heated and forms steam, the water level in the heater chamber drops. If the evaporated water is not replaced quickly enough, the heater chamber will run dry such that the water level becomes too low to cover the heater element. Operating the heater element when it is not completely immersed in water can lead to considerable damage in the boiler unit.

In order to avoid the boiler unit running dry, the boiler unit is configured to determine if the water level in the heater chamber relative to the pair of separated electrodes is too low using the resistance measured between the pair of separated electrodes or another electrical value that is proportionate to the resistance between the pair of separated electrodes. As is well known, water is more electrically conductive, and therefore less resistive, than air. Hence, if the electrodes are immersed in water, a low resistance is seen between them whereas a big resistance is seen if the water level is below the electrodes. So, the boiler unit can compare the measured electrical value (e.g. resistance, conductivity or current) to a predetermined value to determine whether the water level in the heater chamber relative to the pair of separated electrodes is too low.

As the position of the electrodes relative to the heater element is known, determining whether the water level is too low relative to the electrodes can be used to determine whether the water level is too low relative to the heater element. To make this simple, one of the electrodes may be positioned proximate an uppermost edge of the heater element. For example, at least one of the electrodes may be positioned at the same height or substantially the same height as an uppermost edge of the heater element. This allows the boiler unit to determine whether the heater element is fully immersed in the water. The uppermost edge of the heater element is the edge positioned at the highest vertical point in the heater chamber when the boiler unit is placed in its intended operating orientation. For example, the boiler unit may have a base upon which the boiler unit is supported when placed on the ground, thereby defining the intended operating orientation. Determining the water level at or above the uppermost edge of the heater element can be achieved by positioning the electrodes horizontally in line with the uppermost edge of the heater element as viewed with the boiler unit in its intended operating orientation. In addition to the heater element and electrodes, the boiler unit may further comprise a water inlet located in a wall of the heater chamber to allow water to flow into the heater chamber, and a steam outlet located in a wall of the heater chamber to allow steam to exit the heater chamber. The boiler unit may further comprise a conduit connected at a first end to the steam outlet which is configured to carry steam away from the heater chamber. The conduit may comprise a connector at a second end which is connectable to a steam vent of an apparatus for steaming animal fodder (such as a hay steamer) and/or a hose pipe.

The boiler unit may further comprise a water tank connected to the heater chamber such that water stored in the water tank can flow to the heater chamber through the water inlet. A flash heater may provide the heater chamber and heater element. Also, the volume of the heater chamber may be small relative to the volume of the water tank. For example, the volume of the water tank may be at least five or at least ten times larger than the volume of the heater chamber. In some embodiments, the volume of the water tank may be at least five or at least ten times larger than the free volume of the heater chamber where the free volume of the heater chamber is the capacity of the heater chamber to hold water (i.e. the internal volume of the heater chamber less the volume occupied by the heater element).

When the boiler unit determines that the water level relative to the electrodes is too low, the boiler unit may be configured to allow more water to flow into the heater chamber. This will ensure that the heater element remains immersed in water.

The boiler unit may be configured such that, when the boiler unit is allowing water to flow into the heater chamber, the boiler unit prevents more water from flowing into the heater chamber if the boiler unit determines that the water level in the heater chamber relative to the pair of separated electrodes is no longer too low. The water flow is stopped because the water level in the heater chamber has risen sufficiently that the heater element is fully immersed in the water and the pair of separated electrodes are measuring the resistance of water, rather than air. This prevents the heater chamber from being overfilled, for example to prevent water from flowing out of the heater chamber through a steam outlet. Also, the boiler unit may be configured to continue determining whether the water level in the heater chamber relative to the pair of separated electrodes is too low such that the boiler unit operates repeated cycles of allowing and preventing water to flow into the heater chamber.

Optionally, when the boiler unit determines that the water level relative to the electrodes remains too low for longer than a predetermined period, the boiler unit may be further configured to switch off the heater element automatically and/or prevent water from flowing into the heater chamber. A fault is assumed if the water level remains too low, even when the boiler unit is operating to allow water to flow into the heater chamber. This fault may be a stuck valve, a pump not operating correctly, a blockage in the water supply or a leak in the heater chamber. In any event, not enough water is reaching the heater chamber to immerse the heater element, and so the boiler unit shuts itself down. This automatic switch off avoids the risk of the heater element operating when the heater chamber has run dry which may damage the boiler unit.

There is also provided an apparatus for steaming animal fodder, such as a hay steamer, comprising any of the boiler units described above. The boiler unit may be housed in or attached to the main body of the apparatus so as to form an integral unit. Alternatively, the boiler unit may be a separate or standalone unit connected to the main body of the apparatus by a conduit adapted for carrying steam generated in the boiler unit. The conduit may be flexible, for example a hose.

In a second aspect, there is provided a method of determining whether a water level in a heater chamber of a boiler unit is too low relative to a pair of separated electrodes located within the heater chamber. The method comprises measuring an electrical value corresponding to either the resistance between the pair of separated electrodes or another electrical value that is proportionate to the resistance between the pair of separated electrodes. The method further comprises determining whether the water level relative to the pair of separated electrodes is too low using the measured electrical value. Further optional features are set out in the dependent claims, and broadly correspond to the steps described above with respect to the boiler unit.

In a third aspect, there is provided an apparatus for steaming animal fodder, for example a hay steamer. The apparatus comprises a main body including an internal chamber in which the animal fodder may be placed, a water supply and a flash heater comprising a heater chamber housing a heater element. The flash heater is configured to generate steam from water supplied from the water supply. The apparatus also comprises a steam path configured to carry steam generated in the flash heater to one or more steam vents. The one or more steam vents are arranged to introduce steam into the internal chamber of the main body where the animal fodder is placed. The one or more steam vents may introduce steam directly into the animal fodder within the internal chamber or into the chamber externally of the animal fodder so that the steam may then pass into the animal fodder. For example, the one or more steam vents may introduce steam beneath a hay bale, from where the steam will rise through the hay bale.

The term flash heater is used to describe boilers that provide near instantaneous water-to-steam generation. For example, water contained in the heater chamber in contact with the surface of the heater element is almost instantly boiled by the energy transferred from the heater element. The large transfer of energy causes the temperature of the water in the heater chamber to rise almost instantaneously to boiling point, producing steam in a very quick and energy efficient manner.

The flash heater may include a heater element with a large surface area to ensure an increased contact area with water held in the heater chamber. The large surface area may be provided by a heater element having an external surface that extends over a convoluted or serpentine path. Such a path leads to pockets of water between adjacent portions of the heater element, for example in the gaps between adjacent parts of a spiral structure. The result is a heater element with a large surface area to volume ratio.

The heater element may have an external surface with overlapping portions arranged in a side-by-side manner. The heater element may comprise a finned structure like a finned tube. The finned tube may comprise a stem and one or more fins extending outwardly from the stem. An array of fins may extend side by side. Alternatively a single helical fin may extend around the stem, thereby providing overlapping portions of the fin. More than one such helical fin may be provided. The stem may comprise a resistive element configured to generate heat that is then conducted by the stem and one or more fins. To increase further the surface area of the heater element, the one or more fins may have a rippled or wavy profile, or may be serrated or slotted.

Another way to ensure rapid boiling of water in the flash heater is to minimise the amount of water to be heated by the heater element. For example, this may be achieved by keeping the volume of the heater chamber small relative to the volume of the heater element. For example, the heater element may occupy most of the volume inside the heater chamber and/or the volume of the free space in the heater chamber around the heater element is less than half the volume of the heater chamber. This limits the free space around the heater element.

Further advantages are obtained by using a flash heater, for example using a heater element with a convoluted or serpentine shape, or a finned heater element, and hence a large surface area to volume ratio. A volume of water has only a certain amount of limescale that it may deposit, so the amount of limescale deposited per unit area of the heater element is much reduced. This leads to more efficient heating of the water as less energy is lost to raising the temperature of thicker limescale deposits, quicker boiling of the water due to the poor conductivity of the limescale leading to slower heat transfer to the water, and also leads to greater longevity of the flash heater. The reduction in limescale deposits per unit area leads to less need to descale the boiler unit, and less need to replace burnt-out heater elements. A further advantage is obtained through using a finned heater element. The finned heater element may comprise fins extending from a support, wherein the fins are joined only to the support. This creates a cantilevered structure that can vibrate thereby helping reduce limescale deposits. For example, such fins have been found to vibrate at, or substantially at, a frequency of 50 Hz, the same as that of the AC electrical supply provided to the heater element. These vibrations break up and loosen limescale deposits that accumulate on the surfaces of the heater element over time. This helps maintain the flash heater’s high boiling efficiency by limiting the amount of limescale buildup on the surfaces of the heater element.

Another advantage obtained by using a flash heater is that the temperature of the heater element may be reduced. The increased surface area means that a reduced temperature may still lead to increased heat transfer to the water in the heater chamber. This reduction in the temperature of the heater elements results in less pitting and corrosion of the heater element.

The boiler unit may be integral with the main body of the apparatus for steaming animal fodder or attached to the main body of the apparatus for steaming animal fodder. For example, the flash heater may be positioned in a recess provided in the base of the main body, below a platform for placing the fodder in the apparatus. Alternatively, the flash heater may be part of a separate or standalone boiler unit, connected to the main body of the apparatus for steaming animal fodder through a conduit that carries the steam generated in the boiler unit. The conduit may be provided with a connector for connecting the separate boiler unit to the main body using a complementary connector provided on the main body. Using a separate unit allows portability, so the unit can be used with a variety of different types of steaming apparatus.

Also, the apparatus for steaming animal fodder of the third aspect may include a boiler unit according to the first aspect, or any of the boiler units described above with respect to that first aspect. In these embodiments, the heater chamber and heater element are provided by the flash heater.

In a fourth aspect, there is provided an apparatus for steaming animal fodder, for example a hay steamer. The apparatus comprises a main body including an internal chamber in which the animal fodder may be placed, a water supply and a boiler unit comprising a heater chamber housing a heater element. The boiler unit is configured to generate steam from water supplied from the water supply. The apparatus also comprises a steam path configured to carry steam generated in the flash heater to one or more steam vents. The one or more steam vents are arranged to introduce steam into the internal chamber of the main body where the animal fodder is placed. The one or more steam vents may introduce steam directly into the animal fodder within the internal chamber or into the chamber externally of the animal fodder so that the steam may then pass into the animal fodder. For example, the one or more steam vents may introduce stem beneath a hay bale, from where the steam will rise through the hay bale.

The apparatus may determine when the heater element should be descaled. For example, the boiler unit may comprise a temperature sensor configured to measure the temperature of the heater element. The apparatus may be configured to determine if the temperature indicated by the temperature sensor has risen to or above a maximum temperature limit to indicate that a descaling operation should be performed. The apparatus may be configured to indicate that a descaling operation should be performed each time the measured temperature equals or exceeds the maximum temperature threshold. Alternatively, the apparatus may be configured to indicate that a descaling operation should be performed if the measured temperature indicated by the temperature signal equals or exceeds the maximum temperature threshold more than a predetermined number of times within a certain time period. The presence of limescale reduces the efficiency of heat transfer to the surrounding water, and this reduced heat loss from the heater element sees its temperature rise higher.

As a further alternative, the apparatus may be configured to determine a rate at which the temperature measured by the temperature sensor has risen and, if the rate is below a threshold rate, indicate that a descaling operation should be performed. The temperature sensor may be configured to measure the temperature rise of the heater element itself, or of the water in the heater chamber. Some of the energy provided to the heater element is lost in raising the temperature of the limescale such that the water sees a less rapid rise in temperature.

The apparatus may be configured to effect a descaling operation in which the heater element is heated to a raised temperature (raised relative to normal operation during steaming) and/or the heater element is heated for a prolonged time (prolonged relative to normal operation during steaming).

The boiler unit may be housed in or attached to the main body of the apparatus so as to form an integral unit. Alternatively, the boiler unit may be a separate or standalone unit connected to the main body of the apparatus by a conduit adapted for carrying steam generated in the boiler unit. The conduit may be flexible, for example a hose.

LIST OF FIGURES

In order that the invention can be more readily understood, reference will now be made by way of example only, to the accompanying drawings in which: Figure 1 is a perspective view of a hay steamer when shut;

Figure 2 is a perspective view of the hay steamer of Figure 1 when open;

Figure 3 is a perspective view of the hay steamer comprising an integrated boiler unit;

Figure 4 is a detail of the boiler unit of Figure 3;

Figure 5 is a perspective view of a hay steamer with a separate boiler unit;

Figures 6A, 6B and 6C are perspective views of a separate boiler unit;

Figure 7 is a perspective ghosted view of the heater chamber;

Figure 8 is a perspective view of the heater element of the heater chamber of Figure 7;

Figure 9 is a perspective view of the electrode of the conductivity sensor; and

Figure 10 is a schematic diagram showing the steps performed to determine when the boiler unit has run dry.

DETAILED DESCRIPTION

Figures 1 and 2 shows a hay steamer 100. Although described as a hay steamer 100, it will be understood that the hay steamer 100 is not limited to steaming hay. For example, the hay steamer 100 may be used for steaming other types of animal fodder such as straw, silage and haylage. The hay steamer 100 may also be used for growing plants, fruits and vegetables. For example, the hay steamer 100 may be used to pasteurise straw or other substrate when growing mushrooms.

The hay steamer 100 resembles a wheeled-trunk, and has a size suitable for containing a standard-sized hay bale 102. The hay steamer 100 has a main body 104 comprising a lower part 116 and an upper part 118. The lower part 116 and the upper part 118 are joined by hinges such that the upper part 118 may be rotated up and clear of the lower part 116 to open the hay steamer 100 and provide access for loading and unloading a hay bale 102. Figure 2 shows the hay steamer 100 with the upper part 118 raised in the open position, and with a hay bale 102 loaded into the interior of the hay steamer 100.

As can be seen, the interior of the hay steamer 100 forms a chamber 128 shaped and sized to accommodate a standard-sized hay bale 102. The hay bale 102 rests on the floor 122 so as to cover a set of apertures provided in the floor 122 that function as a set of steam vents 154. Steam is delivered under pressure through the steam vents 154 such that the steam enters the hay bale 102. The steam is generated by a boiler unit 200 which may be an integral unit or a separate unit.

Figures 3 and 4 show a hay steamer 100 with an integral boiler unit 200 that, in this particular example, is located in a recess 166 provided in the underside 164 of the lower part 116 of the hay steamer 100. The boiler unit 200 includes a water tank 210, a heater chamber 220, a pump 230 and a controller 240 (see the detail of Figure 4). Hoses 250, 250a, 250b connect the water tank 210 to the pump 230, the pump 230 to the heater chamber 220, the heater chamber 220 to the three steam vents 154, and the heater chamber 220 to an external outlet 255. Wires 260 connect the controller 240 to a power supply (not shown), the heater chamber 220, the pump 230, and to a user interface 270 provided on the upper part 118 of the hay steamer 100.

The water tank 210 is located in a bay 212 formed in the underside 164 of the lower part 116 and is provided with a handle 214 such that the water tank 170 may be easily removed for refilling. In this example, the water tank 210 may be filled with up to 3.5 litres of water. The tank 210 is provided with a connector 216 (such as a push fit connector) that co-operates with a complementary push fit connection 218 provided at the end of a hose 250a that extends to the heater chamber 220. A feeder hose 252 also connects to the complementary push fit connection 218, and the feeder hose 252 extends into the water tank 210 through the filling hole provided in the push fit connector 216. The end of the feeder hose 252 is provided with a downward bend such that it draws water from the bottom of the water tank 210. The complementary push fit connection 218 provided on the hose 250a may also be used to provide a direct connection to a hose pipe (not shown) for when a suitable mains water supply is available. The feeder hose 252 is disconnected and a hose pipe provided with the common type of push fit connector may be connected to the hose 250a via the complementary push fit connection 218.

In either arrangement, water from the water tank 210 or the hose pipe flows to the pump 230 via hose 250a, and then onto the heater chamber 220. Water flow to the heater chamber 220 is controlled by the controller 240 operating the pump 230 and an inlet valve (not shown). A check valve can be used to prevent water flowing back into the pump 230. Steam created in the heater chamber 220 flows to the steam vents 154 from three outlets of the heater chamber 220, from where it passes through the hay bale 102, thereby killing spores and dust particles in the hay bale 102. Steam delivery is controlled by the controller 240 using a valve set 280 located at the outlets of the heater chamber 220 to the steam vents 154 to allow any or all of the steam vents 154 to be selected.

The components housed within the recess 166 are protected by a sump guard 290.

During operation, a user can select a steaming cycle by pressing an appropriate start button provided on the user interface 270. This sends a signal to the controller 240 to pump water to the heater chamber 220, and turn on the heater chamber 220 to boil the water and create steam. As the steam is produced, the pressure in the heater chamber 220 is monitored by the controller 240. When the pressure reaches a threshold pressure, the controller 240 operates the valve set 280 to allow steam to flow to one or more of the steam vents 154 and into the hay bale 102. The hot steam will rise through the hay bale 102, thereby removing and killing the bacteria, mould spores, fungi and dust particles present in the hay bale 102.

During the steaming process, the controller 240 commands the pump 230 to pump more water from the water tank 210 to the heater chamber 220 as required, as will be described in more detail below. At the end of operation, any water and steam remaining in the heater chamber 220 may be purged via the external outlet 255. This outlet 255 discharges steam to atmosphere from a safe location on the underside 164 of the hay steamer 100. The external outlet 255 may also be used to relieve pressure in the heater chamber 220 should the heater chamber 220 and/or controller 240 malfunction and allow too great a pressure to build up in the heater chamber 220.

Figure 5 shows a hay steamer 100 with a separate boiler unit 200. Most of the features of the separate boiler unit 200 are the same as for the integral boiler unit 200 describe above, and so will not be described in detail again to avoid undue repetition. The major difference is that the separate boiler unit 200 is contained within a boiler unit body 310 that is connected to the main body 104 of the hay steamer 100 by a hose 300.

The main body 104 of the hay steamer 100 may be like the hay steamer 100 of Figures 1 and 2, and like that of Figure 3 but without the boiler unit 200 provided in the recess 166 in the underside 164 of the main body 104. The hay steamer 100 may be of other designs though, for example like the hay steamer described in GB Patent Publication No. 2,338,167 in which case the boiler unit 200 described herein may be a replacement for the boiler unit of GB 2,338,167.

Steam generated by the separate boiler unit 200 of Figure 5 is delivered to a folddown outlet connector 302. One end of the hose 300 connects to the boiler unit 200 at the outlet connector 302 via a first coupling 303 such that steam produced by the boiler unit 200 may pass along the hose 300. The fold-down outlet connector 302 may be folded down from its attachment point on the side of the boiler unit body 310 to allow the hose 300 to be connected via the first coupling 303. The other end of the hose 300 connects to the main body 104 of the hay steamer 100 via a second coupling 304. Hence, steam from the separate boiler unit 200 is provided to the main body 104 of the hay steamer 100. The couplings 303 and 304 may be push-fit connectors or the like.

The second coupling 304 connects to a pipe or similar that allows steam to pass to the interior 128 of the hay steamer 100 where the hay bale 102 resides. For example, one or more conduits may connect the second coupling 304 to apertures opening into the interior 128, such as the steam vents 154 provided in the floor 122 of the hay steamer 100 of Figures 1 and 2. The one or more conduits may include a manifold and, optionally, valves to allow steam to be delivered to all steam vents 154 or any subset of steam vents 154.

Figures 6A, 6B and 6C show the separate boiler unit 200 of Figure 5 in greater detail. As mentioned above, the separate boiler unit 200 of Figures 6A-C includes many of the same features as the integrated boiler unit 200 of Figures 3 and 4. For example, the separate boiler unit 200 includes a water tank 210, a heater chamber 220, a pump 230 and a controller 240. Hoses 250 connect the water tank 210 to the pump 230, the pump 230 to the heater chamber 220, the heater chamber 220 to an external outlet 255 and, in the case of the separate boiler unit 200, the heater chamber 220 to a outlet connector 302. The components housed in the recess 166 in the bottom of the separate boiler unit 200 may be protected by a cover that is omitted from Figure 6C for clarity (the fold-down outlet connector 302 is also omitted from Figure 6C for clarity).

The water tank 210 is accessed via a filler cap 308. The water tank 210 has a large capacity relative to the heater chamber 220, for example 3.5 litres of water. When a suitable mains water supply is available, a hose pipe (not shown) may be connected directly to the separate boiler unit 200 via hose connector 312.

In either arrangement, water from the water tank 210 or the hose connector 312 flows to the pump 230 via hose 250, and then onto the heater chamber 220. Water flow to the heater chamber 220 is controlled by the controller 240 operating the pump 230. Steam created in the heater chamber 220 flows to the outlet connector 302 and on to the main body 104 of the hay steamer 100 via hose 300. Steam delivery is controlled by the controller 240 using a valve 280 located at the outlet of the heater chamber 220 to allow steam to pass to the outlet connector 302. Unlike the integrated boiler unit 200 of Figures 3 and 4, the heater chamber 220 has only a single outlet because there is only a single outlet connector 302 to feed, whereas the integrated boiler unit 200 of Figures 3 and 4 had a heater chamber 220 with three outlets that independently provide steam to each of the three steam vents 154.

As described previously with respect to the hay steamer 100 of Figures 1 to 4, a user selects a steaming cycle by pressing an appropriate start button provided on a user interface 270. In the example of Figures 5 and 6, the user interface 270 is provided on the top of the boiler unit body 310 rather than on the main body 104 of the hay steamer 100.

Figure 7 shows a heater chamber 220 that may be used in any of the boiler units 200 described above. The heater chamber 220 houses a heater element 400 that is also shown in Figure 8. The heater element 400 bolts onto a mounting flange 402 that, in turn, bolts on to an open end of the heater chamber 220. The heater element 400 is roughly cylindrical in shape and extends most of the way into the heater chamber 220 and extends across most of the width of the heater chamber 220, leaving only a small volume between the heater element 400 and the inner wall of the heater chamber 220.

As best seen in Figure 8, the heater element 400 comprises a core or stem 404 to which is joined a helical fin 406 that extends along the length of the stem 404. The fin 406 may be welded to the stem 401 . Both the stem 404 and the fin 406 are made of a good heat conductor, for example a metal. The stem 404 encases a resistive heating element to which electrical current is provided via an electrical connector 408 that projects from the heater chamber 220. When current is passed through the resistive heating element under direction of the controller 240, heat is generated that is conducted by the stem 404 and fin 406, and then onto water in contact with the heater element 400, thereby “flashing” the water (i.e. boiling the water rapidly) due to the large surface area of the heater element 400. For example, the heater element 404 may have a surface area of the order of 55,000 mm ² .

The capacity of the heater chamber 220 is small relative to that of the water tank 210 which may be 3.5 litres or more. For example, the free capacity of the heater chamber 400 may be around 630 ml (i.e. the capacity of the heater chamber 220 less the volume occupied by the heater element 400 may be around 630 ml). In operation, the water level in the heater chamber 220 is kept just above the uppermost edge of the heater element 400 (as will be described below with reference to Figure 10). This may amount to 430 ml of water in the heater chamber 220, leaving 200 ml of headspace for the steam that is generated by the heater element 400.

Water is fed into the heater chamber 220 through a water inlet 410 located beneath a steam outlet 412. In operation, the water inlet 410 sits beneath the water level in the heater chamber 400 and the steam outlet 412 sits above the water level. The water inlet 410 is connected to the pump 230 and the steam outlet 412 is connected to the steam vents 154.

The heater chamber 220 is provided with a conductivity sensor to help prevent run dry situations where the heater element 400, or part of the heater element 400, is not immersed in water. The conductivity sensor comprises a pair of electrodes connected to the controller 240. The anode is provided by the tip 416 of a conductivity probe 414, shown in greater detail in Figure 9. The conductivity probe 414 screws into the side of the heater chamber 400 such that the tip 416 of the probe 414 is held at a desired level of the water in the heater chamber 400 during operation, i.e. at or around the uppermost edge of the heater element 400. In use, the controller 240 raises the voltage of the tip 416 above ground potential. The body of the heater chamber 220 is made of metal and so may be used as the cathode in the conductivity sensor. The metallic screw threads 418 provided on the conductivity probe 414 and the heater chamber 400 provide an electrical conduction path to the heater chamber 220 that acts as an effective earth. The tip 416 of the conductivity probe 414 is isolated from the screw thread 418 of the conductivity probe 414 by an electrically-insulating spacer 420. Hence a potential difference is set between the tip 416 of the conductivity probe 414 and ground (the body of the heater chamber 220). The controller 240 measures the current flow from the tip 416 to ground, and hence determines the resistance across the electrodes of the conductivity sensor. A comparison to a predetermined value indicates to the controller 240 whether or not the tip 416 is immersed in water. If the tip 416 is immersed in water, the resistance will be relatively low and the current flow relatively high, and vice versa if the tip 416 is not immersed in water. The controller 240 may directly determine whether or not the tip 416 is immersed in water from values of resistance it determines, e.g. the controller 240 may determine the voltage it set on the tip 416 and combine this with the measured current to calculate the resistance. Alternatively, the controller 240 may indirectly determine whether or not the tip 416 is immersed in water, for example by merely comparing the current measured against a predetermined current value (measuring a current in excess of the predetermined value indicates a relatively low resistance and hence the presence of water).

Figure 10 is a schematic diagram showing a method 500 of operating the heater chamber 220 using a water level detector. The method starts at 502, where a user has initiated a steaming sequence using the user interface 270. The method proceeds along two independent paths.

A first path 501 takes the method 500 to a routine that constantly monitors for a switch-off signal. This switch-off signal may arise from the user manually stopping the steaming sequence using the user interface 270 or from an automatically generated switch off signal, for example generated by the controller 240 when it determines that the steaming sequence is complete. Steps 504 and 506 monitor for a switch-off signal and: a) if no switch-off signal is detected, continues the monitoring steps 504 and 506, or b) if a switch-off signal is detected, the method 500 begins a shut-down procedure 560 which is described in more detail below.

The second path 503 leads to step 510 where the controller 240 starts the flow of water from the water tank 210 to the heater chamber 220. This may be done by switching on the pump 230 or by opening a valve if a gravity-fed system is employed.

After a delay 510, of say 10 or 15 seconds, corresponding to the time in which the heater chamber 220 is expected to fill such that the heater element is submerged, the value of the electrical resistance R between the electrodes of the water level detector is determined by the controller 240 (or the controller determines the value of another electrical value that is proportional to the electrical resistance R). At 515, the controller compares the value of R (or the other electrical value) so determined to a threshold to determine whether the water level has reached the electrodes of the water level sensor. A value higher than the threshold indicates that the heater element is not yet submerged, and so filling should continue. Hence, the method 500 returns to the step 514 of determining R (or the other electrical value) via delay 512. The delay may be shorter on subsequent passes through step 512, for example 1 second.

However, prior to delay step 512, a fault check is performed by the controller 240 at step 518 to ensure that the water tank 210 has not run dry, that the pump 230 is not working or that there is not a blockage preventing water from reaching the heater chamber 220. Step 518 sees the controller 240 compare a time value provided by a clock that starts when the user initiates the steaming sequence at step 502 to ensure it has not breached a threshold time duration. If it has, a fault is assumed to be preventing the heater chamber 220 from filling with water in which case the method 500 proceeds to the shut-down procedure 560.

When step 516 senses that the heater element 400 is submerged by virtue of a low value of R (or the other electrical value) being determined at step 514, the method 500 proceeds to step 520 where the controller 240 turns on the heater element and to step 522 where the controller 240 stops the flow of water, for example by turning off the pump 230.

The controller 240 then continues monitoring the value of the electrical resistance R between the electrodes of the water level detector at step 523. The controller 240 measures successive values of R (or the other electrical value) at a predetermined rate, for example one per second or one per 0.1 s and determines when the values of R (or the other electrical value) have become persistently high, thereby indicating that the heater element 400 is no longer submerged in water. For example, the controller 240 may wait for five consecutive high values of R (or values of the other electrical value indicating that the heater element 400 is no longer submerged in water) before proceeding to step 524 where the controller starts the flow of water to the heater chamber 220, such as by starting the pump 230.

While the heater chamber 220 fills with water once more, and after a delay at step 526 (for example, 1 second), the controller 240 continues to monitor R (or the other electrical value) at step 528 and compare the value of R (or the other electrical value) to a threshold at step 530. While R remains high, indicating a low water level, the controller 240 continues with the delay, determine R and compare R to a threshold steps 526, 528 and 530 (and similarly for the other electrical value if that is used). A fault check 532 is also performed by the controller 240, in the same way as at step 518, to determine whether a fault is preventing the heater chamber 220 from filling with water. If a fault is detected, the method 500 proceeds to shut-down procedure 560.

When the controller 240 determines a low value for R at step 530 (or similarly for the other electrical value if that is used), indicating that the heater element 400 is once more immersed in water, the method 500 returns to step 522 where the controller 240 stops the flow of water once more. The method 500 may then continue through repeated loops of detecting when the water level has dropped enough to begin filling with water once more, followed by steps of detecting when the water level is high enough again to stop the flow of water. This continues until the controller 240 determines that the steaming sequence is complete and issues a switch-off signal, or until the user manually stops the steaming sequence using the user interface 270 or the controller 240 detects a fault at either step 518 or step 530.

Once a shut-down procedure 560 is triggered at step 506, 518 or 532, the method proceeds to step 562 where the controller 240 switches off the heater element 400, and then to step 564 where the controller 240 stops the flow of water to the heater chamber 220 (for example, by stopping the pump 230) thereby causing the method 500 to end at step 566.

A person skilled in the art will appreciate that the above embodiments may be varied in many different respects without departing from the scope of the present invention that is defined by the appended claims.

In the above embodiment, a hay steamer 100 is described. However, the hay steamer 100 is not limited to steaming only hay. For example, the hay steamer 100 may be used for steaming any type of animal fodder such as straw, silage and haylage. The hay steamer 100 may also be used for growing plants, fruits and vegetables. For example, the hay steamer 100 may be used to pasteurise straw or other substrate when growing mushrooms. The hay steamer 100 may be used to steam silage in bales or in loose form.

The hay steamer 100 resembles a wheeled-trunk, and has a size suitable for containing a standard-sized hay bale 102. The hay steamer 100 can also be sized to hold half-sized and other sized bales, or loose hay.

While the lower part 116 and the upper part 118 are described above as being joined by hinges, other arrangements are possible. For example, the lower part 116 and the upper part 118 need not be joined at all, such that the upper part 118 may be lifted from the lower part 116 when the hay steamer 100 is to be loaded and unloaded. The capacity of the water tank 210 may also be varied, as too may that of the heater chamber 220. It is advantageous for the capacity of the water tank 210 to be greater than that of the heater chamber 220, but it is not essential. For example, the capacity of the water tank 210 may be five or ten times greater than that of the heater chamber 220

The integral boiler unit 200 of Figures 3 and 4 is described as having three outlets to connect to the three steam vents 154. However, a single outlet may be provided that feeds one or more manifolds that split the common steam flow from the heater chamber 220 into separate steam paths for the three steam vents 154. The valves of the valve set 280 would be placed downstream of the manifolds to control steam delivery to each of the steam vents 154.

The heater element 400 of Figure 8 is described as having a core or stem 404 to which is welded a helical fin 406 that extends along the length of the stem 404. In addition, the helical fin 406 may have a rippled or wavy profile to increase the heater element’s surface area. The heater element 400 may comprise more than one such helical fin 406. Alternatively, the heater element 400 may comprise fins extending outwardly from the stem 404 as an array of fins extending side by side. The array of fins may be serrated or slotted. The fins may be joined only to the stem 404. The extension of the fins from the stem 404 creates a cantilevered structure that can vibrate, helping to reduce and limit the buildup of limescale deposits. In one example, such fins have been found to vibrate at, or substantially at, a frequency of 50 Hz, the same as that of the AC electrical supply provided to the heater element 400. These vibrations break up and loosen limescale deposits that accumulate on the surfaces of the heater element 400 over time, thereby maintaining a high boiling efficiency.

In another example, the heater element 400 may have an outer surface that extends over a convoluted or serpentine path to increase the surface area.

The controller 240 may also monitor the boiler unit 200 to determine when the heater element 400 should be descaled. For example, a temperature sensor may measure the temperature of the heater element 400. The controller 240 may then determine if the temperature indicated by the temperature sensor has risen to or above a maximum temperature limit to indicate that a descaling operation should be performed. The controller 240 may indicate that a descaling operation should be performed each time the measured temperature equals or exceeds the maximum temperature threshold. Alternatively, the controller 240 may indicate that a descaling operation should be performed if the measured temperature indicated by the temperature signal equals or exceeds the maximum temperature threshold more than a predetermined number of times within a certain time period. The presence of limescale reduces the efficiency of heat transfer to the surrounding water, and this reduced heat loss from the heater element 400 sees its temperature rise higher.

As a further alternative, the controller 240 may determine a rate at which the temperature measured by the temperature sensor has risen and, if the rate is below a threshold rate, indicate that a descaling operation should be performed. The temperature sensor may measure the temperature rise of the heater element 400 itself, or of the water in the heater chamber 220. Some of the energy provided to the heater element 400 is lost in raising the temperature of the limescale such that the water sees a less rapid rise in temperature.

A descaling operation may effect descaling by heating the heater element 400 to a raised temperature (raised relative to normal operation during steaming) and/or heating the heater element 400 for a prolonged time (prolonged relative to normal operation during steaming).