GB2098708A

GB2098708A - A water heater

Info

Publication number: GB2098708A
Application number: GB8214343A
Authority: GB
Original assignee: TORMEN SHEET METAL UK Ltd
Current assignee: TORMEN SHEET METAL UK Ltd
Priority date: 1981-05-15
Filing date: 1982-05-17
Publication date: 1982-11-24
Also published as: GB2098708B

Abstract

A water heater having the facility to preselect the desired amount of water to be heated and then automatically fill its tank and heat that quantity of water ready for use. The heater has a tank (51) with a water inlet (2) controlled by a powered valve (4), an outlet (6) closed by a tap (7), the operation of the powered valve (4) being controlled by an adjustable water level sensor (50) by means of which the amount of water to be heated in the tank can be selected, a heater (55) to heat water in the tank to a preselected temperature at which the heater is switched off by a thermostat connected thereto, the heater (55), sensor (50) and valve (4) being electrically connected via a main switch (52) so that having selected the required quantity of water to be heated using the adjustable sensor (50), then with the main switch (52) activated, the tank will be filled to the level of the selected amount of water and heated to said temperature automatically. <IMAGE>

Description

SPECIFICATION An improved water heater This invention relates to water heaters and more particularly to a heater which can be plumbed-in to a domestic water supply for use in place of a normal electrical kettle.

Electric kettles suffer from many disadvantages.

For instance, they usually stand on a kitchen work surface and therefore take up valuable space thereon. They also require an electric flex to be plugged into them and this can be hazardous if it is done with wet hands without first turning off the mains electricity supply. On boiling, considerable quantities of steam are given off through the kettle spout which exposes the user to the risk of scalding. Steam activated switches have been used to switch the kettle off soon after it has boiled but even so considerable quantities of steam are still expelled before the heater element can be switched off which is undesirable.

It is an object of the invention therefore to provide a water heater which will overcome or substantially reduce these problems.

According to the invention, there is provided a water heater comprising a tank having an inlet connectible to a water supply and an outlet closed by a valve, a powered valve in the inlet controlled by an adjustable water level sensor in the tank, said sensor being operable by a user to select the amount of water to be admitted to the tank, a heater operable to heat the water in the tank to a preselected temperature at which the heater is switched off by a temperature responsive switch connected thereto, the heater, sensor and inlet valve being electrically connected and arranged via a main switch so that when a user has selected the required quantity of water to be heated using the adjustable water level sensor, then with said main switch activated, the inlet valve is opened to admit water to the tank until it reaches the level set by the water level sensor when it automatically closes and the heater element is switched on to heat the water in the tank to said pre-selected temperature ready for dispensing from the tank via its tap controlled outlet.

Preferably the tank is made of a metal or plastics material.

In a preferred embodiment, the inlet valve is powered by a solenoid which is initially energised when the main switch is activated, and the water level sensor is responsive to the water in the tank reaching the set level to operate an electrical switching element which then deenergises the inlet valve solenoid and switches on the heater element.

The water level sensor can take any convenient form. For instance, it may include a float arm mechanically linked between a water level selector and the electrical switching element. Preferably however, the water level sensor is a probe adjustable in level in the tank by means of a water level selector, the probe being electrically connected in circuit with the electrical switching element so that the latter is operated due to current flow through the probe when the water rises into contact therewith.

The heater element may be connected in series with an inlet valve solenoid of impedance much greater than that of the heater element, across a power supply circuit, said electrical switching element, when operated, acting to short circuit the inlet valve solenoid to de-energise the latter and cause the supply voltage to be applied across the heating element.

In another embodiment, the water level sensor is a series of conductive elements of differing levels on the side wall of the tank and electrically connected in circuit with said switching element to operate the latter responsively to the selective bridging of said conductive elements by a rising water level in accordance with the setting of a water level selector which selectively connects said conductive elements into circuit.

Alternatively, the water level sensor may be a series of photocells arranged at differing levels in the tank and electrically connected in circuit with said switching element to operate the latter responsively to the selective activation of the photocells by a rising water level in accordance with the setting of a water level selector which selectively connects the photocells into circuit.

Preferably, the main switch is connected in series with an overfill switch which is opened by the water level sensor if the water in the tank rises above a predetermined level. Conveniently, the main switch is connected in series with a thermostatically controlled tank-dry switch and with a switch which is opened and closed with operation of the tap controlled outlet.

In a preferred embodiment, a step down transformer and rectifier are provided whereby the heater, inlet valve and associated circuitry are operable at a selected d.c. voltage from an a.c. mains power supply.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a schematic view of a water heater of the invention with a float type water level sensor; Figure 2 is a perspective view of the heater of Figure 1 but with its lid removed; Figure 3 is a front view of the heater of Figures 1 and 2; Figure 4 is a circuit diagram of the heater of Figures 1 to 3; Figure 5 shows an alternative embodiment using another type of water level sensor; and Figure 6shows another embodiment similar to that of Figure 5 but incorporating a transformer.

Referring to the drawings, there is shown a water heater or "wall kettle" comprising a tank 1 having an inlet 2 connectable at 3 to a water supply. It is preferred that the heater be plumbed-in to the water mains thereby avoiding the need to place it over a sink or to have to use a flexible feed from an existing tap. Avalve 4 is located intermediate the mains connection point 3 and the inlet 2. This valve is preferably a solenoid valve and is normally closed whereby water will only be admitted to the tank 1 on energisation of the solenoid in the manner to be described hereafter.

The tank 1 also has an overflow 5 positioned below the level of the water inlet 2 so that there is always an air gap between the inlet and the water level to prevent possible contamination of the water mains due to back siphonage. At the bottom of the tank there is an outlet pipe 6, preferably located centrally of the tank body, this being controlled by a tap 7. As a safety feature, the tap 7 has a microswitch 8 (see Figure 4) associated therewith which is electrically connected to the main electric power supply to the heater to switch it off should the tap be left open inadvertantly. Thus, the risk of the contents of the tank emptying straight onto the kitchen worktop during filling is avoided.

The heater is also provided with two other main controls namely an on/off switch 12 and a water level selector knob 18 which is connected in a manner to be described to an adjustable water level sensor such as a single or double float 9 in the tank. By means of this knob, a user can select or dial the number of cups of water to be heated. In the illustrated embodiments, this is in the range from 1 to 6 cups but a different range can be readily provided for by suitable modification of the apparatus if required. A marker 10 in the form of a float in a sight tube 11 provides an external visual indication of the level of water in the tank at any time but this is not essential.

The on/off switch 12 can either be a simple switch e.g. a push/push switch or alternatively it can incorporate means whereby the temperature to which the water is to be heated may be selected. In the illustrated arrangement, the switch 12 is electrically connected to a thermostat 13 (see Figure 2) which automatically switches off heater 14 when the water boils.

The float 9 is connected by a link member 16, pivotted at 17 and connected to an actuating rod 32 at pivot 33. The knob 18 has a link arm 19 secured thereto which is pivotally attached to a wedge member 20. The latter is movable horizontally on rotation of the knob 18 between the free end of actuating rod 32 and changeover microswitch 21. As can be seen from Figure 1, the upper surface of part of the wedge member 20 is flat whereas its lower edge 23 is inclined, the free end of the actuating rod 32 resting on the wedge member 20 under it own weight thereby keeping the contact fingers 23 of the microswitch 21 depressed until such time as the float 9 is freely floating on the surface of the water in the tank when it has reached the preselected level for the number of cups selected by the knob 18.Once this happens, the microswitch 21 changes over and switches the power supply from the solenoid valve 4 (so it returns automatically to its normally closed position and the water supply is cut off) to the heater 14 and the water in the tank 1 is heated up until it reaches the cut-off temperature of the thermostat 13 and is switched off automatically. The heated water is then ready to be drawn off via outlet 6 as required, any steam not capable of being contained in the tank venting to the exterior through the overflow opening 5.

Should the solenoid valve 4fail to close due to an electrical fault, the tank could continue to fill up beyond the selected level, say 4 cups. However, to avoid any risk of an overflow resulting from this malfunction, when the water level reaches second float 24, it will activate microswitch 25 associated therewith which in turn switches off the supply to the main on/off switch 12 thereby cutting off the power supply to the valve 4 which will then return to its normally closed condition and shut off the water supply.

One form of tank 1 can be better seen in Figure 2. It can be made from any suitable water tight material such as metal or a mouldable synthetic plastics e.g.

"Acetal" which will not deform when the water in it is boiled. The illustrated tank is divided into 3 compartments by partitions 26,27 and thermostat 13 being located on one of these. A floor 28 extends between the partitions at the height of the slot 5 in the front wall of the tank, the floor sloping slightiy backwards towards a gap 29 between its end adjacent rear wall 30 of the tank. Water from the inlet 2 is directed through the gap 29 to fill the tank. The purpose of the chamber defined by the partitions 26, 27, the floor 28 and the front and rear walls 30,31 of the tank is that it provides an expansion chamber in which any steam generated on boiling can dissipate and condense, the condensate running back along the floor 28 into the tank.With this arrangement, very little steam actually comes out of the front slot 5 on boiling so the risk of scalding is substantially reduced. It will also be appreciated that in the unlikely event that there should be a malfunction resulting in the tank overfilling,the water will rise up through the gap 29 and flow out of the whole appliance through the front slot 5.

Referring now to Figure 4, the electrical relationship between the various components can be seen.

In use, the user selects the amount of water required by means of knob 18 (see Figures 1 and 3) and activates the On switch 12, conveniently a thermostatic capillary type switch. Power is applied via NC/COMM overfill switch 25, COMM/NO outlet open switch 8, on/off switch 12 and COMM/NO water level switch 21 to the motorised water valve 4 which then opens and allows water to flow into the tank 1.

The water level float 9 (see Figure 1) rises until it reaches the selected water level when the actuating rod 32 lifts off the microswitch 21 which changes to its NC condition and switches off the power supply to the motorised valve 4, which then closes and stops any further flow of water into the tank, and connects the power to the heating element 14. When the selected water temperature has been reached, the on/off switch 12 returns to its off position.

The water is now ready to be drawn off via the outlet tap 7. When the outlet is opened, outlet open microswitch 8 operates disconnecting power from the switch 12.

If all the water is drawn off, the float 9 falls and changes over the water level microswitch 21 to its NO condition so that the kettle is ready for re-use.

Conveniently, a neon light 45 is provided to indicate Power-on, a light 46 to indicate that the outlet tap 7 is open, and a light 47 to indicate that the heater 14 is on. Audio alarms can be provided instead of lights and a visual or audio signal can be included to indicate that the operating cycle is complete.

The described embodiment has the following safety features:1. The water level float preferably consists of two separate floats 9 joined together ensuring that if one float punctures, the other will still operate the water level microswitch.

2. Should both water level floats puncture, water will continue to fill the tank until the overfill float 24 is reached when it rises and operates microswitch 25 breaking the electrical power supply to the kettle.

3. The outlet tap 7 has a microswitch 8 operably associated with it which changes over from the NO to NC condition, disconnecting any possibility of the motorised valve 4 receiving power. This prevents water flowing into the tank if the On switch 12 is activated with the outlet tap 7 open.

4. Should the On/Off switch 12 fail in the On condition, the water will boil away and when the water level has fallen sufficiently, the water level float switch 21 changes over to its No condition and allows more cold water to flow into the tank. The kettle will cycle like this until manually switched off, at the power source, and an audible steam whistle will be heard continuously whilst the kettle is boiling, thereby warning the user of the malfunction.

5. Should all fail and the heater 14 is switched on with no water in the tank, a boil dry thermostat (not shown) switches the unit off. A metal heat shield is preferably fitted under the heating element to prevent possible damage if a plastic tank is used.

6. Should the water supply fail and the kettle is switched on, the motorised valve 4 remains open but no hazard will arise because it is continuously rated.

Figure 5 shows an alternative embodiment using a different type of adjustable water level sensor arrangement comprising a pivotally mounted movable metal rod 41 which is connected to selector knob 18 (not shown) so as to be pivotable up and down about pivot point 42. This rod is electrically connected to the junction of the heater element 14, the solenoid valve 4 and a TRIAC switch 44. A fixed metal rod 43 is also mounted in the tank 1 and electrically connected to the gate of the TRIAC switch 44.

When the kettle is switched on by means of the ON/OFF switch 12, provided that the tap outlet switch 8 is closed, power is supplied via its NO contacts to the heating element 14 and the water solenoid valve 4 to neutral. The TRIAC switch 44 at this time is open. As the solenoid valve 4 resistance is very high compared to that of the heating element 14, nearly all the applied voltage develops across the solenoid valve 4 which opens and allows water to be admitted to the tank 1.

When water bridges rods 42 and 43, current flows through the water to the TRIAC gate which causes the TRIAC switch to close thereby connecting the heating element to neutral and short circuiting the solenoid valve 4 which then closes and stops any further flow of water into the tank 1.

The heater then heats up the contents of the tank until it reaches the required temperature when a thermostat 13 (not shown) switches off the heater in exactly the same way as has been described in relation to the embodiment of Figures 1 to 4.

It will be seen that with this arrangement by adjusting the position of the movable rod 41, a very simple but effective water level sensing system is provided because as soon as the water level reaches the bottom of the rod 41, it provides an electrically conductive bridge between the two rods 41 and 43 which causes the TRIAC switch 44 to switch on the heater 14 and close the solenoid valve 4.

Figure 6 shows an alternative arrangement incorporating a transformer 53 to step the voltage down from 240 volts ac to for instance 12 volts dc in the interests of safety. The arrangement of the mechanical elements is similar to that of the embodiment already described in that it comprises a tank 51 having a water inlet 2 controlled by a solenoid activated valve 59. The tank has a water outlet 6 controlled by a cap 7 a heater 14 is provided in the base of the tank to heat the water admitted thereto. A probe arm 50 is pivotally mounted in the tank and its position relative to the bottom of the tank can be adjusted by suitable rotation of a dial on the exterior of the tank.

The tank will include an overflow as well as a temperature responsive switch such as a thermostat or thermistor to switch off the heater when the water in the tank reaches the required temperature.

The operation of the illustrated device is as follows. Assuming the water level is not touching the bottom of the adjustable probe 50, when capillary on/off switch 52 is activated, providing the outlet 6 to the tank 51 is not open, power is connected to the primary winding of mains transformer 53, and one side of the heating element, neon light 54 indicating that the kettle is switched on. The second winding of the transformer 53 delivers a low voltage output which is half-wave rectified by diode 56, smoothed by capacitor 57 and the resultant low voltage direct current is applied across the transistor 58. The heating element 55 is connected in series with the solenoid valve 59 in the water inlet 2. Triac switch 60 is open at this time and current flows through the heating element 55 and the solenoid 59.The electrical impedance of the solenoid 59 is much greater than that of the heating element 55 so nearly all the voltage is developed across the solenoid which opens and water flows into the tank 51. The voltage across the heating element 55 is so small that the heating effect it produces can be ignored.

The electircal resistance across the gap between the end of the probe 50 and probe 61 mounted in the base of the tank 51 is usually very high and virtually no current flows into the base of the transistor 58 which is not conducting. When the water level bridge probes 50 and 61, the electrical resistance between them drops instantly, the water acting as a conductor, allowing current to flow into the base of the transistor 58 which switches it into a conducting state. The relay 62 operates and contacts 63 close connecting the gate of the Triac switch 60 to the junction of the heating element 55 and the water solenoid 59. The Triac switch 60 closes, shortcircuiting the water solenoid 59 which closes and stops the water flowing into the tank 51. The water solenoid 59 is now short-circuited so that full power is developed from the heating element 55 to heat the water.When the desired water temperature has been reached, the on/off switch 52 switches to the off position thereby turning of the heating element.

Float operated overfill switch 64 opens, disconnecting the electrical power to the appliance if it tends to overfill with water at any time. Thermostat switch 65 opens, disconnecting the electrical power to the kettle should the kettle tend to overheat. This switch does not recycle and remains off until manually reset with a special tool.

When the water outlet 6 is open to drain the tank 51, switch 66 changes over and power is disconnected from the heating element 55 and the mains transformer 53 and connected to a neon light indicator 67 which shows that the outlet is open thereby preventing further filling of the tank with water and/or heating.

It should also be made clear that the main on/off switch in the above-described embodiments is preferably a switch entirely separate from the water level selector control. Thus in the case when a user wishes to maintain the selector at a chosen water level most of the time, the heater can be repetitively used without touching the level selector. When the main switch is again turned on under such circumstance, the tank will fill to the level which was previously set, regardless of the amount of water drawn off in the meantime. However, it is within the scope of the invention to embody the on/off switch and the level selector in an integrated control device, which will then preferably include a restoring means which, when the heater is switched off, returns the water level selector to zero.

The overflow and location of the thermostat are not critical to the invention so they may be arranged differently from the positions shown in the drawings. For instance, the overflow can be an upstanding tube extending from the bottom of the tank upwardly through the base to a point just below the water inlet. With such an arrangement, the thermostat can be located in the portion of the tube which projects from the base of the tank. This enables the steam to build up in the tank as the water is heated and to then flow down the overflow pipe to the steamstat which is then activated. Any excess steam can vent from the tank via the overflow.

Whilst the described embodiments show a manually controlled outlet valve 7, it can be motorised or solenoid operated valve if required.

Claims

1. A water heater comprising a tank having an inlet connectible to a water supply and an outlet closed by a valve, a powered valve in the inlet controlled by an adjustable water level sensor in the tank, said sensor being operabe by a user to select the amount of water to be admitted to the tank, a heater operable to heat the water in the tank to a preselected temperature at which the heater is switched off by a temperature responsive switch connected thereto, the heater, sensor and inlet valve being electrically connected and arranged via a main switch so that when a user has selected the required quantity of water to be heated using the adjustable water level sensor, then with said main switch activated, the inlet valve is opened to admit water to the tank until it reaches the level set by the water level sensor when it automatically closes and the heater element is switched on to heat the water in thetankto said preselected temperature ready for dispensing from the tank via its valve controlled outlet.

2. A water heater according to claim 1, wherein said tank is made of metal or plastics material.

3. A water heater according to claim 1 or claim 2, wherein the inlet valve is powered by a solenoid which is initially energised when the main switch is activated, and the water level sensor is responsive to the water in the tank reaching the set level to operate an electrical switching element which then deenergises the inlet valve solenoid and switches on the heater element.

4. A water heater according to claim 3, wherein the water level sensor includes a float arm mechanically linked between a water level selector and said electrical switching element.

5. A water heater according to claim 3, wherein the water level sensor is a probe adjustable in preset levels in the tank by means of a water level selector, and said probe is electrically connected in circuit with said electrical switching element so that said switching element is operated due to current flow through the probe when the water rises into contact therewith.

6. Awater heater according to claim 5, wherein the heater element is connected in series with an inlet valve solenoid of impedence much greater than that of the heater element, across a power supply circuit, said electrical switching element, when operated, acting to short circuit the inlet valve solenoid to de-energise the latter and cause the supply voltage to be applied across the heating element.

7. A water heater according to claim 3, wherein the water level sensor is a series of conductive elements at differing levels on the side wall of the tank and electrically connected in circuit with said switching element to operate the latter responively to the selective bridging of said conductive elements by a rising water level in accordance with the setting of a water level selector which selectively connects said conductive elements into circuit.

8. A water heater according to claim 3, wherein the water level sensor is a series of photocells arranged at differing levels in the tank and electrically connected in circuit with said switching element to operate the latter responsively to the selective activation of the photocells by a rising water level in accordance with the setting of a water level selector which selectively connects the photocells into circuit.

9. A water heater according to any of claims 1 to 8, wherein the main switch is connected in series with an overfill switch which is opened by the water level sensor if the water in the tank rises above a predetermined level.

10. Awater heater according to claims 1 to 9, wherein the main switch is connected in series with a thermostatically controlled tank-dry switch and with a switch which is opened and closed with operation of the tap controlled outlet.

11. A water heater according to any of claims 1 to 10, including a step down transformer and rectifier whereby the heater, inlet valve and associated circuitry are operable at a selected d.c. voltage from an a.c. mains power supply.

12. A water heater substantially as herein described with reference to the accompanying drawings.