ANTI-SIPHONING DEVICE

TECHNICAL FIELD

This invention relates to an anti-siphoning device, and in particular, to an anti- siphoning device for preventing backflow from a dentist's water supply.

BACKGROUND OF THE INVENTION

Backflow in a mains water supply is flow in a reverse direction from normal. Thus, instead of water flowing from the water supplier to the consumer, water flows back into the main supply. When a temporary drop in water pressure occurs, water can be siphoned back into the mains water supply. Siphoning is caused by negative pressure in the supply piping caused by, for example, a break in the pipe at a low point in the supply line, high flow velocities in the mains pipe lines, or high water withdrawal elsewhere in the mains supply system. Backflow can lead to contamination of the mains water supply as contaminated water may be drawn or siphoned into the main supply.

According to the invention we provide an anti-siphoning device comprising a storage reservoir for receiving water from the mains water supply through an inlet, an overflow means to prevent water in the storage reservoir from rising beyond a predetermined level, at least two supply reservoirs that receive water from the storage reservoir, each supply reservoir being connected to a water outlet, and sensor means for detecting when the water level in either supply reservoir reaches a high level or a low level and when the water level is low, water is allowed to flow from the storage reservoir to the appropriate supply reservoir to refill it, and when the water level is high, the flow of water from the storage reservoir to the supply reservoir is prevented and the supply reservoir is pressurized, wherein the device includes switching means constructed and arranged such that when one of the supply reservoirs is being refilled the switching means is adapted to connect one of the other supply reservoirs to the water outlet.

The use of a storage reservoir and at least two supply reservoirs is particularly advantageous as the arrangement ensures effective anti-siphoning without the performance of the device suffering. Thus, a pressurized water supply is available to the user from the supply reservoirs. This combination of features results in a particularly effective and reliable anti-siphoning device. This device has applications in hospitals,

photograph developing laboratories, dentist's and doctor's surgeries and laboratories in general, for example.

Preferably, the device includes two supply reservoirs, which supply water to the water outlet alternately. Preferably, water is consumed from one reservoir, while the other reservoir is refilled from the storage reservoir. Preferably, a switching means is provided that connects the appropriate supply reservoir to the water outlet depending on whether the reservoir is ready to dispense water.

Preferably, the pressure of the mains water supply is regulated by a regulating valve. The mains inlet to the storage reservoir may be controlled by an inlet control valve. Preferably, the valve is a pilot operated 3/2 valve. Preferably, the inlet control valve is actuated by a water inlet pilot control solenoid valve. Alternatively, the flow may be controlled by a solenoid valve.

The storage reservoir may include a sensor that determines when the water level in the reservoir has reached a predetermined high level and accordingly acts on the inlet control valve to close it. Thus, by having a sensor acting directly (or through a control system) on the inlet control valve, the water level in the storage reservoir is maintained and overflowing is prevented. The storage reservoir may also include a backup sensor that also detects when the water level in the storage reservoir has reached a predetermined point. This is advantageous as if the high level sensor fails; there is a further sensor that ensures an air gap is maintained between the water level in the storage reservoir and the water inlet. Preferably, the storage reservoir also includes a low level sensor that is adapted to cause water to flow into the storage reservoir.

Preferably, the overflow means comprises an overflow weir that is connected to a drainage system. The overflow means is preferably spaced from the water inlet in the storage reservoir. Preferably, the high level and back-up sensors and overflow means are arranged such that a rising water level in the reservoir is first detected by the high level sensor, then the back-up sensor and lastly drains into the overflow means.

Preferably, the anti-siphoning device is for supplying water to dental tools.

Dental tools may include a dentist's drill, a spittoon, or a polishing device, for example. Preferably, a diaphragm valve controls the flow of water between the storage reservoir and each supply reservoir. Preferably, the diaphragm valve is constructed and arranged such that when the supply reservoir is pressurized it closes preventing water

flow into the supply reservoir. Alternatively, the diaphragm valves may be controlled by a pilot valve.

Preferably, an air control valve in the form of a solenoid valve controls the supply of pressurized air to the supply reservoir. A regulating valve may regulate the pressurized air supply. This ensures that the supply reservoir is pressurized to an acceptable level to displace the water therein to the water outlet, but also so that the pressure is not high enough to potentially cause damage to the device or a user of the device.

Preferably, the air control valves are connected to pressure switches that are adapted to cause the air control valves to close in the event of loss of pressure from the pressurized air supply. Preferably, the pressure switches cut the electrical power to the air supply valves in the event of loss of pressure from the pressurized air supply.

Preferably, the or each supply reservoir includes a high level sensor that detects when the water level in the reservoir is at a predetermined high level. Preferably, the signal output by the high level sensor causes the prevention of the flow of water from the storage reservoir and the supply reservoir to be pressurized.

Each supply reservoir may also include a low level sensor that detects when the water level in the reservoir is at a predetermined low level. Preferably, the signal output by the low level sensor when it detects that the water level is low causes the supply reservoir to depressurize and causes water to flow into it from the storage reservoir.

Preferably, the water inlet includes a nozzle, the nozzle including a water straightening device.

ASPECTS According to an aspect of the invention, an anti-siphoning device (1) including a fluid supply (2) and a fluid outlet (3), the anti-siphoning device (1) comprises: a storage reservoir (4) in fluid communication with the fluid inlet (2); and two or more supply reservoirs (7, 8) in fluid communication with the storage reservoir (4) and in fluid communication with the fluid outlet (3); wherein the two or more supply reservoirs (7, 8) are adapted to receive fluid from the storage reservoir (4) and provide a pressurized fluid supply to the fluid outlet (3).

Preferably, the storage reservoir (4) further comprises a high level sensor (22) adapted to indicate when the storage reservoir (4) contains a predetermined amount of fluid.

Preferably, the anti-siphoning device (1) further comprises a backup high level sensor (23).

Preferably, the storage reservoir (4) further comprises an overflow weir (20).

Preferably, the storage reservoir (4) further comprises a low level sensor (50) adapted to signal a low fluid level in the storage reservoir (4).

Preferably, the signal from the low level sensor (5) opens a flow path from the fluid inlet (2) to the storage reservoir (4).

Preferably, the anti-siphoning device (1) further comprises a valve (11, 12) adapted to control fluid communication between the storage reservoir (4) and a supply reservoir of the two or more supply reservoirs (7, 8).

Preferably, pressurization of a supply reservoir of the two or more supply reservoirs (7, 8) closes the valve (11, 12) thereby preventing fluid communication between the storage reservoir (4) and the supply reservoir.

Preferably, a pilot valve (51, 52) actuates the valve (11, 12) that is adapted to control fluid communication between the storage reservoir (4) and the supply reservoir.

Preferably, a supply reservoir of the two or more supply reservoirs (7, 8) further comprises a low fluid level sensor means (30, 30') adapted to signal a low fluid level in the supply reservoir (7, 8).

Preferably, the signal provided by the low fluid level sensor means (30, 30') causes a valve (11, 12) to open to allow fluid communication between the storage reservoir (4) and the supply reservoir (7, 8) from which the signal was sent. Preferably, the signal provided by the low fluid level sensor means (30, 30') de- pressurizes the supply reservoir (7, 8) from which the signal was sent.

Preferably, the supply reservoir (7, 8) further comprises one or more semi- autodrains (53, 54) adapted to de-pressurize the supply reservoir (7, 8).

Preferably, a supply reservoir of the two or more supply reservoirs (7, 8) further comprises a high fluid level sensor means (31, 31') adapted to signal a high fluid level in the supply reservoir (7, 8).

Preferably, a supply reservoir (7, 8) of the two or more supply reservoirs (7, 8) further comprises a drainage output (35, 37).

Preferably, the storage reservoir (4) is positioned above the two or more supply reservoirs (7, 8) such that the two or more supply reservoirs (7, 8) receive fluid from the storage reservoir (4) under a gravitational force.

Preferably, the anti-siphoning device (1) further comprises a drainage output (35, 37) in fluid communication with each of the two or more supply reservoirs (7, 8) and in fluid communication with a drainage system.

Preferably, the fluid inlet (2) further comprises a fluid straightening device. According to another aspect of the invention, a method for operating an anti- siphoning device, the anti-siphoning device comprising: a storage reservoir in fluid communication with a fluid inlet; and two or more supply reservoirs in fluid communication with the storage reservoir and in fluid communication with a fluid outlet; the method comprises the steps of: filling the storage reservoir with fluid from the fluid inlet; filling a first supply reservoir of the two or more supply reservoirs with fluid from the storage reservoir; pressurizing the first supply reservoir; and opening a fluid flow path between the first supply reservoir and the fluid outlet, thereby providing a pressurized fluid supply to the fluid outlet. Preferably, the step of filling the first supply reservoir comprises de-pressurizing the first supply reservoir and allowing fluid to flow into the first supply reservoir under a gravitational force.

Preferably, the step of pressurizing the first supply reservoir closes a fluid flow path between the storage reservoir and the first supply reservoir.

Preferably, the method further comprises the step of closing the fluid flow path between the first supply reservoir and the fluid outlet when a low level sensor detects a low fluid level.

Preferably, the method further comprises the step of filling at least a second supply reservoir of the two or more supply reservoirs with fluid from the storage reservoir.

Preferably, the method further comprises the step of pressurizing the second supply reservoir and alternately opening a fluid flow path between the first supply reservoir and the fluid outlet and the second supply reservoir and the fluid outlet.

Preferably, the method further comprises the step of draining the anti-siphoning device using one or more drainage outputs (35, 37) when the anti-siphoning device is no longer in use.

BRIEF DESCRIPTION OF THE DRAWINGS

There now follows by way of example only a detailed description of the present invention with reference to the accompanying drawing in which:

Figure 1 shows a diagrammatic view of an embodiment of the present invention in the form of a dental water dispenser; and

Figure 2 shows a second embodiment of the invention. DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 & 2 and the following description depict specific examples to teach those skilled in the art how to make and use the best mode of the invention. For the purpose of teaching inventive principles, some conventional aspects have been simplified or omitted. Those skilled in the art will appreciate variations from these examples that fall within the scope of the invention. Those skilled in the art will appreciate that the features described below can be combined in various ways to form multiple variations of the invention. As a ^" result, the invention is not limited to the specific examples described below, but only by the claims and their equivalents.

FIG. 1 shows an anti-siphoning device 1 that is for use in the field of dentistry and is adapted to receive potable water from the mains supply 2 and deliver it, via a water outlet 3, to a dentists' drill (not shown) or spittoon (not shown), for example. It will be appreciated that the anti-siphoning device 1 could be used in any field where preventing contamination of the water supply is important.

The device 1 comprises a storage reservoir 4 for potable water. The water is received from the mains supply 2 through an inlet 5, which is controlled by an inlet

control valve 6. The device 1 also comprises two supply reservoirs 7, 8, each having a reservoir outlet 9, 10. The reservoir outlets 9, 10 both connect with the water outlet 3. The supply reservoirs 7, 8 receive water from the storage reservoir 4 through diaphragm valves 11, 12. The supply reservoirs 7, 8 are adapted to be pressurized by pressurized air from air supply 13. A regulating valve 14 regulates the pressurized air supply 13. The supply of pressurized air to each supply reservoir 7, 8 is controlled by air control valves 15, 16 respectively. The air control valves 15, 16 receive pressurized air from the air supply 13 and are 3/2 normally closed solenoid valves.

The flow of water from the main water supply 2 is regulated by regulator valve 17 before it enters the storage reservoir 4. The valve 6 controls the flow of water into the storage reservoir 4 and is of Fellbach valve cartridge pilot operated 3/2 type. The valve 6 includes a pilot air input 44, which is received from the air supply 13 and controlled by water inlet pilot control valve 45. The pilot control valve 45 is a 3/2 normally closed solenoid valve. The storage reservoir 4 is located above the supply reservoirs 7, 8 so that water can flow to them from the storage reservoir 4 under gravity when diaphragm valves 11, 12 are open. The reservoir 4 is open to atmosphere by virtue of aperture 18. The reservoir 4 includes a sidewall 19, which has an aperture 20 therein which acts as an overflow weir. The overflow 20 is of non-circular design and is connected to a standard drainage system (not shown). The storage reservoir 4 includes a liquid level sensor system 21 comprising two sensors 22 and 23. The sensors 22, 23 are attached to a support rod 24, which depends from a cover part 25 of the reservoir 4 and is connected to a sensor interface 26. The cover part 25 is mounted to the upper edge of the sidewall 19. The interface 26 allows signals from the sensors 22, 23 to be conveyed to a control system (not shown). Both of the sensors are located adjacent but below the level of the overflow 20. The lowermost sensor 22 is a high level sensor and the uppermost sensor 23 is a backup high level sensor. The sensors 22, 23 are used by the control system to determine when the level of water in the storage reservoir 4 has reached a predetermined point, determined by the location of the sensors 22, 23 along rod 24. Each supply reservoir 7, 8 comprises a vessel having walls 26, continuous with the sidewalls 19 of the storage reservoir 4, and a base part 27 and a partition part 28, which separates the supply reservoir 7, 8 from the storage reservoir 4. Diaphragm

valves 11, 12 are located in the partition part 28, and the reservoir outlets 9, 10 are located at the base part 27. The pressurized air supply 13 is received through the wall 26 via supply lines 29, 29'. The reservoirs 7, 8 each include water level sensors 30, 30', 31, 31 ' which are connected to the control system and are mounted to a support rod 32, which depends from the partition part 28. Sensors 30, 30' are located adjacent but spaced from the base part 27 and are used by the control system to determine when the water level in the supply reservoirs 7, 8 respectively is low. Sensors 31, 31' are located adjacent but spaced from the partition part 28 and are used by the control system to determine when the water level in the supply reservoirs 7, 8 respectively is high. The supply reservoir outlets 9, 10 include pilot operated supply reservoir outlet valves 33, 34. The valves 33, 34 are of Fellbach valve cartridge pilot operated 3/2 type. Valve 33 has two outputs; a drainage output 35, which connects to a standard drainage system (not shown), and a supply output 36, which connects with water outlet 3. Similarly, valve 34 has a drainage output 37 and supply output 38. The pilot valves 33, 34 are controlled by a pilot air supply 39, which is received from the main air supply 13 and controlled by a pilot control valve 40. The pilot control valve 40 is a 3/2 normally closed solenoid valve. The supply outputs 36 and 38 from supply reservoirs 7, 8 respectively are received by a switching block 41. The switching block 41 incorporates a Fellbach valve cartridge pilot operated 3/2. The block 41 receives a pilot air supply 42, which is received from the main air supply 13 via a pilot control valve 43. The pilot control valve 43 is a 3/2 normally closed solenoid valve. The switching block 41 determines which of the supply outputs 36, 38 is connected to the water outlet 3.

The control system (not shown) receives electrical signals as input from the sensors 22, 23, 30, and 31 and provides output in the form of actuating signals to the pilot control valves 15, 16, 40, 43, and 45. Application of an output signal to any of the valves 15, 16, 40, 43, or 45 causes the solenoid to actuate and, as the valves are normally closed, the valve will open allowing the pressurized air from supply 13 to flow through the valves 15, 16, 40, 43, and 15. The control system of the anti-siphoning device has three operating modes: a start-up mode, a normal operation mode, and an end mode.

When no power is supplied to the device 1, it will be empty of water and no pressurized air will be supplied, as valves 15, 16, 40, 43, and 45 are biased closed. This

state is shown in FIG. 1 in which all the valves 15, 16, 40, 43, 45 are connected to atmosphere. Thus, when the control system enters start-up mode, signals are sent to pilot control valves 15, 16, which allows air from the supply 13 to enter the supply reservoirs 7, 8. The air supplied to the reservoirs 7, 8 acts on the diaphragm valves 11, 12 causing them to close and therefore prevents communication between the storage reservoir 4 and the supply reservoirs 7, 8. The control system then sends a signal to the control valve 45, which provides a pilot signal to open water inlet valve 6. Thus, regulated water from the mains supply 2 flows into the storage reservoir 4. The water in the reservoir 4 is at atmospheric pressure as the reservoir 4 is open to atmosphere by virtue of the aperture 18.

The water level in reservoir 4 will continue to rise as a signal is continued to be supplied to control valve 45 until the control system receives a signal from high level sensor 22, indicating that the reservoir 4 contains a predetermined amount of water. When the signal is removed from valve 45 it closes, thereby closing valve 6 preventing further water entering the storage reservoir 4 from the mains supply 2. Further, in response to the signal received from the sensor 22, pilot control valve is actuated by application of a signal, thus causing the supply reservoir outlet valves 33, 34 to open. The signal to control valves 15, 16 is also removed thereby allowing the pressurized air in the supply reservoirs 7, 8 to exhaust to atmosphere via a silencer (not shown) at 46. Thus, as the supply reservoirs 7, 8 are no longer pressurized, the diaphragm valves 11 , 12 will open thereby allowing water from the storage reservoir 4 to flow, under gravity, into both the supply reservoirs 7, 8.

The control system maintains this state until the high level sensors 31, 31' indicate that the water in the supply reservoirs 7, 8 is at a high level. On receipt of a signal from each high level sensor 31, 31' the respective control valve 15, 16 is actuated to pressurize the appropriate supply reservoir 7, 8, which causes the appropriate diaphragm valve 11, 12 to close, preventing further water from the storage reservoir 4 entering the supply reservoirs 7, 8. The control system applies a signal to pilot control valve 43, which causes the switching block 41 to accept water supplied from supply reservoir 7 to water outlet 3. This completes the start-up mode and an indication of this, in the form of the illumination of a light for example, may be supplied to the user of the device.

The anti-siphoning device 1 is now ready for normal use and thus the control system enters normal operation mode. The dentist's equipment consumers water through water outlet 3 from either of the supply reservoirs 7, 8 as selected by the state of the switching block 41. By default, after the start-up mode reservoir 7 is selected. As the water is consumed the water level in reservoir 7 will decrease until it reaches the level of sensor 30. When the control system receives a signal from sensor 30, that the water level in the reservoir 7 is low, a signal is sent to pilot control valve 43, which causes the switching block 41 to connect supply output 38 of reservoir 8 to the water outlet 3. Communication between supply output 36 and water outlet 3 is accordingly closed. Thus, water from reservoir 8 is then used without interruption to the water supply to the dentist's tools. Simultaneously, the signal to the pilot air control valve 15 is removed thereby venting the air pressure in reservoir 7 to atmosphere via silencer 46: Diaphragm valve 11 will open due to the loss of air pressure in reservoir 7, which allows water from the storage reservoir 4 to flow into supply reservoir 7 thereby refilling it. Water will continue to flow into reservoir 7 until the control system receives a signal from sensor 31 , which indicates that the reservoir 7 has been filled to its predetermined high level. Upon receipt of the signal from sensor 31, air control valve 15 is actuated, which re-pressurizes reservoir 7, closing diaphragm valve 11 preventing further water flow from reservoir 4. Reservoir 7 is now ready to dispense water once the switching block 41 connects it to the water outlet 3.

Similarly, water will now be consumed from supply reservoir 8. When the water level reaches a low level of sensor 30', the pilot control valve 43 causes the switching block 41 to close the connection between water output 38 and the water outlet 3 and connect the outlet 3 to the water output 36 from reservoir 7. Air control valve 16 is also closed, thus venting the air pressure in reservoir 8 to atmosphere via the silencer 46. The loss of pressure in reservoir 8 allows the diaphragm valve 12 to open. Water from storage reservoir 4 therefore flows into the supply reservoir 8 until the water level rises to that of sensor 31 '. The signal from sensor 31' results in air control valve 46 being opened, which re-pressurizes reservoir 8 thereby closing diaphragm valve 12 and preventing further water flow into reservoir 8 from the storage reservoir 4. Reservoir 8 is now ready to dispense water once the switching block 41 connects it to the water outlet 3 in response to the water in reservoir 7 reaching a low level.

It will be appreciated that throughout normal operation the device 1 will repeat the above stages as it dispenses water from the supply reservoir 7 and then supply reservoir 8 and then reservoir 7 again and so on. While each reservoir 7, 8 is connected to the outlet 3, the other reservoir is being refilled ready for use. Thus, the device 1 is able to deliver an uninterrupted supply of potable water by switching between the two supply reservoirs 7, 8.

During normal operation mode, the water level in the storage reservoir 4 will decrease as the water therein is used to fill supply reservoirs 7, 8 in turn. When the sensor 22 detects that the water level in reservoir 4 has dropped, it causes pilot control valve 45 to open valve 6 and allow the regulated flow from mains water supply 2 to enter and refill reservoir 4. When sensor 22 detects that the water level has risen to its high level, pilot valve 45 is closed thereby causing valve 6 to interrupt the supply of water into the reservoir 4. This cycle will be constantly repeated while the device 1 is in normal operation mode. When the dentist or user no longer requires the water supply, they can set the control system to enter the end mode. The signals applied to the valves 15, 16, 40, 43, 45 are removed which causes them to close. This causes water inlet valve 6 to prevent water entering the storage reservoir 4. The air control valves 15 and 16 allow air from reservoirs 7 and 8 to be vented to atmosphere via silencers 46. The diaphragm valves 11, 12 will therefore open allowing the water from the storage reservoir 4 to flow into the reservoirs 7, 8. The closure of pilot control valve 40 causes valves 33 and 34 to connect the water outputs 36 and 38 to the drainage outputs 36 and 37 respectively. The water in the device 1 therefore drains from the storage reservoir into the supply reservoir 7, 8 and then to the drainage system via outputs 35, 37. This completes the end mode and the device 1 is ready to enter the start-up mode when required.

The device 1 includes several safety features to ensure it operates reliably and consistently provides potable water without siphoning of the water back into the mains water supply 2.

In particular, if sensor 22 fails, the water level will rise to the level of backup high level sensor 23. The back up sensor 23 causes the pilot control valve 45 to close which results in closure of the valve 6 to prevent further water from the supply 2 entering the storage reservoir 4. If the backup sensor 23 were also to fail or if the valve

45 were to become jammed open, the water would be able to drain away via the overflow weir 20. This ensures that an air gap is maintained between the nozzle 47 where the water exits the water inlet valve 6 into the reservoir 4 and the water level in the reservoir 4. This is important to prevent siphoning of the water in the reservoir 4 back into the mains supply 2. If air pressure is lost, for example from air supply 13, the valve 6 will prevent water entering reservoir 4 as it will not receive the pilot air input 44. Further, lack of air pressure will allow diaphragm valves 11, 12 to open and the supply reservoir outlet valves 33, 34 to connect the reservoir outlets 9, 10 to the drainage system 35, 37. Thus, any water in the device 1 will drain from the storage reservoir 4, through diaphragm valves 11, 12 into supply reservoirs 7, 8 and then to the drainage system leaving the device empty of water.

The device 1 also incorporates further features that are not shown in the Figure. In particular, the reservoir 4 and nozzle 47 are such that the incoming water cannot splash back or form a mist that can pollute the incoming water supply. The overflow 20 and reservoir 4 is adapted to ensure that an air gap between the water level and nozzle 47 is maintained even if the regulator 17 and valve 6 became stuck open with an incoming water pressure of 10 bar. The diaphragm valves 11, 12 may also incorporate baffles (not shown) so that if the valves 11, 12 were to fail while the supply reservoirs 7, 8 were pressurized, water in the reservoirs would not be blow toward the nozzle 47 or cover part 25, which could potentially lead to contamination of the water supply.

It will be appreciated that while the operation of the system has been described with a control system, it will be appreciated that the signals output by the various sensors 22, 23, 30, 30', 31, 31' may directly control its associated valve. For example, the output of the sensors 30 or 30' may act directly on valve 43 and on the respective air control valves 15 or 16 to cause them to close. Further, the output of the sensors 31, 31' may also act directly on air control valves 15 and 16 to cause them to open. The output of the sensor 22 may act directly on valve 45.

FIG. 2 shows a second embodiment of the invention that includes additional features. Thus, the same reference numerals as in FIG. 1 have been used for like features.

The liquid level sensor system 21 for the reservoir 4 includes a low level sensor 50 in addition to the high level sensor 22 and backup sensor 23. In this embodiment, the

water level in reservoir 4 will drop until it reaches low level sensor 50. In response to the signal from sensor 50, regulated flow from mains water supply 2 is allowed to flow into reservoir 4 until the water level reaches high level sensor 22. As before, the signal from high level sensor 22 causes the interruption of the supply into reservoir 4. In this second embodiment, an inlet water solenoid valve 60 replaces pilot control valve 45. Valve 60 receives water from the mains water supply 2 via a preset flow regulator 61. The flow regulator 61 is adapted such that in the event of failure of valve 60 and with a mains water supply pressure of 10 bar, an air gap between nozzle 47 and the water level in reservoir 4 is maintained. Further, the nozzle 47 includes a water straightening device to ensure incoming water does not splash back or form a mist that can pollute the incoming water supply.

The reservoir 4 includes a plurality of baffles (not shown) to prevent water in reservoir 4 being blown toward nozzle 47 due to a failure of valves 11, 12 releasing pressurized air from reservoirs 7, 8 into reservoir 4. Diaphragm valve 11, 12 are adapted to receive pilot control signals from solenoid valves 51 and 52 respectively. The valves 51, 52 are 3/2 normally closed type. The pilot signals from valves 51, 52 control the opening and closing of the diaphragm valves 51, 52. Thus, in this embodiment, the valves 51, 52 can be opened and closed independently of the pressure in reservoirs 7, 8. Further, the pressure in supply reservoirs 7, 8 is additionally exhausted through semi-autodrains 53, 54 respectively. By using semi-autodrains 53, 54 the reservoirs 7, 8 can be exhausted quickly, thus improving the performance of the device 1 and allowing it to be used in high flow rate applications.

In the embodiment of FIG. 2, the pressurized air supply 13 branches at 57 into two additional pneumatic lines 58, 59 prior to it entering regulating valve 14. The lines 58 and 59 prior to it entering regulating valve 14. The lines 58 and 59 are connected to pressure switches 55 and 56, which in turn control air control valves 15 and 16. The pressure switches 55, 56 are adapted to disconnect the power to valves 15, 16 in the event of a loss of air pressure from the air supply 13. This causes the valves 15, 16 to return to their default closed position allowing the device to be restarted correctly when the air supply pressure returns.

The device 1 is shown surrounded by a cover 62 of ABS plastics material, which protects the device from damage in use. To improve drainage from the device 1 or where drainage under gravity is not possible, a water pump 63 is provided to remove water that has drained from overflow 20, for example, to the waste water drainage system (not shown).

Although present in the first embodiment but not shown, FIG. 2 shows a control means 64. The control means 64 is programmed to cause the valves to open and close in response to the sensors as well as the order in which they are activated on start-up, normal and end modes of operation. In start-up mode, the device of FIG. 2 functions as follows: the biasing of the valves 15, 16, 40, 43, 51, 52, and 60 and the control means 64 ensures that no air pressure, water pressure, or electricity is applied to the device 1. The inlet water solenoid valve 60 is then opened to allow water to flow via the regulator 61 and the water straightener in the nozzle 47 into reservoir 4. Valve 40 is then actuated to cause valves 33, 34 to direct water to the water outlet 3. The storage reservoir 4 and supply reservoirs, 7, 8 will begin to fill with water. When the control means 64 receives a signal from either of the high level sensors 31, 31', which indicates that the water level in the reservoirs 7, 8 is high, the respective solenoid valve 51, 52 is actuated to close its associated diaphragm valves 11, 12. This prevents further flow into the supply reservoir 7, 8. Valves 15 and 16 are then actuated to cause reservoirs 7, 8 to be pressurized with air. The storage reservoir 4 will continue to fill with water until sensor 22 causes the valve 60 to be closed. The control means 64 now generates a signal to the user to indicate that start-up mode is complete and the device 1 is ready for use.

The control means 64 therefore enters normal operation mode. The user will begin to consume water through the switching block 41 and water outlet 3 from supply reservoir 7. It will be appreciated that the device may alternatively begin to dispense water from reservoir 8.

When the water level in reservoir 7 is determined to be low by sensor 30, actuation of valve 43 causes switching block 41 to direct water from reservoir 8 to the water outlet 3. Air is then exhausted from reservoir 7 via the valve 15 and the semi- autodrain 53 opens to aid the exhaustion of air in response to the drop in pressure. Solenoid valve 51 is then deactivated to open diaphragm valve 11 so that reservoir 7

fills with water from storage reservoir 4. When high level sensor 31 is activated, valve 51 is actuated to close diaphragm valve 11 and valve 15 is also actuated to pressurize reservoir 7 with air.

When the water level in reservoir 8 reaches sensor 30' a similar process is performed. Valve 43 causes the switching block 41 to direct water from reservoir 7 to the outlet 3. The valve 16 is deactivated to cause air to be exhausted from the reservoir 8 via the valve 16 and semi-autodrain 54. Solenoid valve 52 is then deactivated to open diaphragm valve 12 so that reservoir 8 fills with water from storage reservoir 4. When high level sensor 31 ' is activated, valve 52 is actuated to close diaphragm valve 12 and valve 16 is also actuated to pressurize reservoir 8 with air.

These two cycles will be repeated during normal operation mode. Further, as water is consumed from reservoir 4, the water level will fall until it reaches sensor 50. The activation of sensor 50 causes control means 64 to open water inlet valve 60. Valve 60 is kept open until the activation of sensor 22 (or back-up sensor 23) indicates that the water in reservoir 4 has reached a high level. This cycle of refilling reservoir 4 is repeated during normal operation.

When the dentist or user no longer requires the water supply, they can set the control means 64 to enter the end mode. Electrical power to solenoid valves 15, 16, 40, 43, 51, 52, and 60 is removed. This causes them to switch to their normally closed condition, which also causes the exhaustion of air from reservoirs 7, 8. Further, the valves 33, 34 will switch from directing water to the switching block 41 to directing water to the drainage system 37. Thus, the device 1 will drain of water.

The control means 64 has means to ensure the controlled shut-down in accordance with the end mode in the event of power failure. Thus, the control means 64 may include a battery so that it can operate without its primary power supply.

The detailed descriptions of the above embodiments are not exhaustive descriptions of all embodiments contemplated by the inventors to be within the scope of the invention. Indeed, persons skilled in the art will recognize that certain elements of the above-described embodiments may variously be combined or eliminated to create further embodiments, and such further embodiments fall within the scope and teachings of the invention. It will also be apparent to those of ordinary skill in the art that the

above-described embodiments may be combined in whole or in part to create additional embodiments within the scope and teachings of the invention.

Thus, although specific embodiments of, and examples for, the invention are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize. The teachings provided herein can be applied to other water supply devices, and not just to the embodiments described above and shown in the accompanying figures. Accordingly, the scope of the invention should be determined from the following claims.