WO1993022714A1

WO1993022714A1 - Electrically controlled valve mixing device

Info

Publication number: WO1993022714A1
Application number: PCT/AU1993/000204
Authority: WO
Inventors: Scott Anthony Milan; Jeffrey James Watts; Howard Stephen Sheeran
Original assignee: Rottwest Pty. Ltd.
Priority date: 1992-05-07
Filing date: 1993-05-07
Publication date: 1993-11-11

Abstract

A device for mixing water supplied to a common outlet from sources of hot and cold water. The device includes: first electrically operable valve means for controlling the supply of cold water to the common outlet; second electrically operable valve means for controlling the supply of hot water to the common outlet; and control means for controlling operation of the first and second valve means whereby temperature of water, at the common outlet is continuously adjustable independent of pressure and vice versa.

Description

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ELECTRICALLY CONTROLLED VALVE MIXING DEVICE

This invention relates to a device for mixing fluids such as water supplied to a common outlet and in particularly to a device for mixing the water supplied from separate sources of hot and cold water and for controlling pressure and/or temperature of the water in the common or mixed water outlet. The mixing device according to the invention is especially suitable for use with domestic taps and it will be convenient to describe the invention with reference to that type of application. However it is to be appreciated that the mixing device can be used in other applications and can be used to mix fluids other than water.

Most domestic taps are manually operated by rotating a tap handle. Operating these taps can be a difficult exercise for disabled and elderly people and accordingly it would be desirable to provide a tap which could be operated and controlled remotely through an easy to operate control unit.

Australian patent application 24440/88 discloses an electrical mixing device for showers or baths which allows a lotion or shampoo to be mixed with water. Temperature control of the mixed water is achieved by regulating hot and cold water valves which are coupled together by gearing such that when the cold-water valve is opened, the hot-water valve is closed and vice versa. Because temperature and pressure of the mixed water cannot be controlled independently a third valve is required to control the pressure of the mixed water. A mixing fitting is also required to allow the temperature of the mixed water to be monitored.

This mixing device is relatively complicated because it requires gearing between the hot and cold water valves, a third valve to control mixed water pressure as well as a mixing fitting for monitoring the mixed water temperature. It is an object of the present invention to at least alleviate the above mentioned disadvantages of the prior art.

According to the present invention there is provided a device for mixing water supplied to a common outlet from sources of hot and cold water, said device including: first electrically operable valve means for controlling said supply of cold water to said common outlet; second electrically operable valve means for controlling said supply of hot water to said common outlet; and control means for controlling operation of said first and second valve means whereby temperature of water at said common outlet is continuously adjustable independent of pressure and vice versa.

The first and second valve means may comprise an electrically operable valve which can be adjusted between open and closed positions to control the supply of hot and cold water to the common outlet. Preferably the valve means comprises an electric motor coupled to a valve. Alternatively the valve means may comprise a proportional opening solenoid valve.

Preferred ^• valves are those which are opened or closed by rotation of an adjustment member such as a spindle or stem. Preferred valves include stainless steel ball valves and needle and seat valves. 1/4 turn ball valves modified as described hereinafter are most preferred. Spindle valves may also be used although they are generally multiturn and require regular maintenance with the replacement of washers. Ceramic disc valves, especially 1/4 turn ceramic disc valves may be used.

Electric motors coupled to valves have been used in industry for process control applications however these motors are large and expensive, the cost being proportional to the size of the job to be done. For domestic situations motorized valves need to be small, simple and inexpensive. In this regard a small reversible DC motor powered by a battery or AC mains (with appropriate transformer, rectifier regulator etc) coupled to the spindle of a ball valve is particularly suitable.

Stepper motors may be used, as well as non-reversible AC or DC motors provided appropriate valves, gearing, couplings, control means etc. are selected.

A small DC motor generally exhibits a small torque at high r.p.m. The spindle of ball valve however requires a relatively high torque at very low turning speeds, preferably in the order of about 2 to 5 rpm, more preferably about 3 rpm. In order to overcome this problem the motor can be coupled to the valve spindle via a high reduction gear box. The reduction gearbox provides a torque multiplication factor, which allows a relatively small electric motor to provide sufficient torque to turn the spindle of the valve.

An advantage of using a small motor with low power consumption is that the motorized valve can be powered by a small battery such as a rechargable sealed lead acid battery supported by a small solar cell. Accordingly the device according to the invention can be given complete independence from the 240V AC mains if desired. This reduces the installation cost and is an extra safety feature of the invention. The battery also guarantees supply during a power failure.

It is also possible to use a needle and seat valve instead of a ball valve. These are usually high precision valves and consequently are expensive. An advantage of using a needle and seat valve is that unlike standard ball valves, they generally provide a linear flow rate response, ie. 25% open = 25% of flow-rate, 50% open = 50% of flow-rate etc. Valves providing a linear flow-rate response are particularly preferred since they facilitate independent adjustment of pressure and temperature.

It has been determined from testing that the range of flow required in a domestic kitchen, bathroom, shower situation is from approximately 3 litres/min to approximately 17 litres/min. In a typical domestic situation with typical mains pressures a 1/2 inch ball valve with a 15 mm orifice will supply 17 litres/min when it is only approximately 35% open. This renders 65% of the valves travel useless and results in poor flow rate control. One method of overcoming this problem is to reduce the diameter of the orifice, eg. to about 8 mm

2 (50 mm ) . This will give a typical maximum flow-rate of about 28 litre/min. Results show that as the size of the orifice decreases the maximum flow-rate decreases and the flow-rate response becomes more linear.

A more preferred method is to modify the shape of the orifice eg. by providing a ball with a slit-shaped orifice rather than a circular orifice. It has been found that a ball with a slit-shaped orifice has a reduced flow rate and more linear flow characteristics than a ball having a circular orifice of the same size.

Another preferred feature of the invention is that hot and cold water are supplied to the device at the same or similar pressures. This is generally the case when both hot and cold water are supplied at mains pressure. If necessary a pressure reducing valve may be located in the cold water supply to reduce the cold water pressure.

Commercially available ball valves generally have a two piece ball and stem arrangement- Lag between movement of the stem and ball can result in undesirable backlash which makes consistent temperature and pressure adjustment difficult. A modification which eliminates backlash is to use a single piece ball and stem. Small backlash parameters are also desirable for the coupling, gearbox and motor. Another important feature of the ball valve is the number of degrees of turn required to move the ball valve from fully open to the fully closed position. This parameter is determined by the relationship between the diameter of the ball and the width of the orifice as illustrated in the following table:

* This is the time taken to turn the valve from fully closed to fully open, assuming a shaft speed of 3 RPM.

The longer response time of 4.2 seconds results in a smoother temperature adjustment and better flow rate control. The response time is also dependent on the relationship between the speed of the motor and the ratio of the gearbox since this governs the speed of rotation of the shaft or stem.

In a preferred embodiment of the invention the device includes limit switches to terminate current supply to the motor when the valve is in a fully opened or fully closed position. It is relatively easy to adapt limit switches to a 1/4 turn ball valve. However it is more difficult to mount limit switches on a multiturn valve such as a needle and seat valve because it is difficult to physically position limit switches so that they are only actuated when the valve is fully opened or fully closed. One way to overcome this problem is through the use of a worm gear on the shaft of the multiturn valve, although other methods would be evident to a person skilled in the art. For valves having spindles which are not free to rotate a full 360°, the limit switches also can act to prevent damage to the motors and gearboxes by terminating curent supply to the motor before the spindle reaches the limit of its travel.

Instead of using a motor/valve combination it is possible to use proportional opening solenoid valves to control the flow of water. Solenoid valves, however, require a constant supply of current when in any position other than fully closed. For this reason they require a greater supply of current than a motor/valve combination.

The control means may take a number of forms depending on the type of electrically operable valve means used and the type of functions required. In one form the control means may be realised via digital control circuits such as a suitably programmed microprocessor or microcomputer. Alternatively the control means may be realised with relays and/or essentially analogue circuits utilizing integrated and/or discrete components. The control means will be described with reference to the control of a pair of electrically operable valve means, such as a D.C. motor coupled to a valve.

The control means may include one or more control buttons or switches to allow an operator to perform the following operations:

1. Supply current having a first polarity to the first valve means causing the first valve means to open.

2. Supply current having a second polarity opposite to said first polarity to the first valve means causing the first valve means to close.

3. Supply current having the first polarity to the second valve means causing the second valvejn ans to open.

4. Supply current having the second polarity to the second valve means causing the second valve means to close. - ι -.

5. Remove the supply of current from the first and/or second valve means thereby stopping the associated valve means at any position between the open and closed position.

In a preferred embodiment of the invention these operations or combinations thereof may be performed using four buttons or switches labelled "ON", "OFF", "HOT" and "COLD" . In this embodiment operation of the ON button or switch may supply current having the first polarity to the first and second valve means causing the first and second valve means to open, release of the button or switch stopping the current supply. Operation of the OFF button may supply current having the second polarity to the first and second valve means causing the first and second valve means to close, release of the OFF button stopping the current flow.

Operation of the COLD button may supply current having the first polarity to the first valve means causing the first valve means to open and/or may supply current having the second polarity to the second valve means causing the second valve means to close, release of the button stopping the current supply. A COLD button performing both operations is particularly advantageous when hot and cold water is supplied to the device at the same pressure ie. mains pressure, and the first and second valve means have linear flow characteristics. This is because operation of the COLD button will alter the temperature without altering the pressure.

Operation of the HOT button may supply current having the first polarity to the second valve means causing the second valve means to close and/or may supply current having the second polarity to the first valve means causing the first valve means to close, release of the button stopping the current supply. For the reasons stated above it is preferred that the HOT button performs both operations. The control means may also include a "one touch OFF" button which allows the operator to close both valves in a single "one touch" operation.

Apart from the one touch "off" button or switch it is preferred that current is only supplied to the valve means while the button is depressed i.e. releasing the button cuts off the current supply. This allows the user to select the required temperature and pressure of water by simply pressing and releasing the buttons.

The mixing device preferably includes means for terminating current supply to the valve means when the valve means is in a fully opened or fully closed position. This may be achieved by the use of microswitches which are activated by an arm protruding from the valve/gearbox coupling when the valve means is in a fully opened or fully closed position. Other means such as optical sensors may also be used.

The control means including the buttons or switches may be located in a single housing which may be mounted on a wall or bench or other convenient location. In a particularly preferred arrangement the electrical components including any transformers, rectifiers etc. are mounted separately from the control buttons or switches. In this embodiment the electrical components may be mounted out of sight in the wall or under a bench. The buttons or switches may be located on a separate remote control pad _which is electrically or functionally connected to the remainder of the electrical components. The remote control pad may then be located safely in a wet area such as in a shower recess, beside a bath or wash basin, etc.

In another embodiment of the invention the control means includes means for sensing temperature and/or pressure in the mixed water outlet. The temperature and/or pressure sensors may be provided as part of a servo motor control system for automatically setting temperature and/or pressure .

Each motor controlled valve may include an encoder for supplying feedback data concerning the position of the motor controlled valve to the servo motor control system.

Desired temperature and/or pressure settings may be inputted to the servo motor system via temperature/pressure preset buttons, switches or the like. The latter may be provided on the remote control pad. Display means for displaying actual temperature and/or pressure may also be provided on the control means or remote control pad or other convenient location. The control means or remote control pad may also include a "ready" light which indicates when the preset temperature and/or pressure is attained. Panel interface of the control units with other electrical fittings such as exhaust fans, lights, radio, intercom, etc. is also envisaged.

In one embodiment the control means includes a central processing unit (C.P.U.) which accepts commands from a control panel, for adjusting the valve means accordingly. By committing to memory a pressure/temperature condition, the CPU can recreate that pressure/temperature condition on command. This can be done by monitoring the actual temperature and pressure at the mixed water outlet via pressure and temperature sensors. Desired pressure and temperature conditions may be memorized by pressing a "memory store" button on the control panel. On recall the CPU will adjust the values until the memorized conditions are recreated.

Preferably the device includes three temperature sensors, one on the cold water inlet, one on the hot water inlet and one on the mixed water outlet. With a requested temperature realized at the mixed outlet the CPU can monitor, via the temperature sensors, any change in temperature at the cold and hot water inlets, and compensate for that change in temperature by making appropriate changes to the valve positions, thereby maintaining the desired mixed water temperature. A flow rate sensor can also be placed at the mixed water outlet if desired.

To be able to adjust the temperature and pressure of the mixed water at the mixed water outlet the CPU may monitor the position of the valve means, either directly or by monitoring the position of the motor, gearbox, coupling member etc. In this regard stepper motors have a number of advantages. Firstly because each pulse corresponds to one specific step angle (eg. 1.8°) there is a higher degree of accuracy of movement and so the processor knows exactly where each motor is. Secondly there is no need for limit switches to indicate the fully open and fully closed positions of the valve. This is because the processor knows how many steps in either direction it takes for the valve to be fully open or fully closed. When the motor has been driven the required number of steps the CPU will stop the motor. This feature is specifically suitable for multiturn valves.

It is also preferable that the CPU has the ability to store and recall a number of different temperature/pressure conditions. This would allow for example a house installation of four or five sets of motorized valves to be controlled by one central controller and power supply, thus reducing the system cost.

Another advantage of using a CPU to control the position of the valves is that any non-linearity in the flow characteristics of the valve means can be compensated for. Also it is possible to include an "antiscold" safety feature into the device. This may be done by allowing an operator to input a maximum allowable temperature via a "maximum temperature" button on the control panel. Once set the CPU may not allow the temperature at the mixed outlet to go beyond the specified temperature. This feature is particularly useful in situations accommodating young children, the elderly and the disabled.

Another safety feature of the invention is that the device may be controlled by a remote control panel or pad which can be located out of reach of small children. For use around the elderly the control panels and buttons can be enlarged to any desired size and placed in any convenient position, depending on the specific needs of the users.

In a combination bath/shower situation one set of electrically controlled taps can replace two sets . of conventional taps. This can be achieved by using the one set of valves to mix the water and then direct it to the shower or bath outlet, ie. by means of a solenoid valve. This valve could be controlled by the central control unit. Preferably the valves are fitted with 1/2" B.S.P. compression fittings to facilitate easy installation into 1/2" copper pipe normally installed in domestic and commercial buildings.

Typical mains pressures in domestic and commercial buildings range from approximately 50 psi to 120 psi. In extreme cases of high mains pressure there would be some advantage in installing pressure regulating valves on the water inlet lines. This would assist smooth operation of the mixing device.

It will be convenient to further describe the invention by reference to the accompanying drawings which illustrate a number of preferred embodiments of the invention. Other embodiments of the invention are possible, and consequently the particularity of the accompanying drawings is not to be understood as superceding the generality of the preceding description of the invention.

In the drawings; Figure 1 is a graphical comparison of valve positions versus flow characteristics for a number of ball valves;

Figure 2 is a representation of a modified ball valve;

Figure 3 is a partial-sectional view of a motor and gearbox coupled to a ball valve;

Figure 4 is a sectional view taken through line 4-4 of figure 3;

Figure 5 is a plan view of pair of motorized valves coupled together via a mixing chamber;

Figure 6 is a circuit diagram of one embodiment of the invention;

Figure 7 is a block diagram of an embodiment of the invention incorporating a central processing unit; and

Figure 8 is a representation of a control panel for a device including a central processing unit.

The flow characteristics plotted in figure 1 were obtained for ball valves having different orifice sizes using a mains pressure of 65 psi. The results show that the flow characteristics become more linear as orifice size decreases. The results also show that a slit-shaped orifice reduces the flow rate and gives more linear flow characteristics when compared to a circular orifice of the same cross-sectional area.

Figure 2 shows a motor 1 coupled to a gearbox 2.

Gearbox 2 is coupled to a ball valve 3. Motor 1 is a high quality, low inertia precision DC reversible motor which has a very low power requirement. Gearbox 2 is a high reduction gearbox with the primary function of reducing rotation of gearbox output shaft 4 to about 3 rpm. The coupling between the gearbox output shaft 4 and stem 5 of ball valve 3 is such that there is low backlash. For this purpose output shaft 4 of gearbox 2 comprises a female hexagonal recess 6. A male hexagonal mold 7 is provided on the end of the valve stem. The mold 7 fits tightly into recess 6 forming a rigid coupling. To further reduce backlash the ball valve 3 comprises a single piece ball stem assembly 5a. Inlet 8 of ball valve 3 is provided with a 1/2 inch BSP compression fitting 9 to facilitate connection to 1/2 inch copper pipe normally installed in domestic and commercial buildings.

Gearbox output shaft 4 is provided with an optical disk 10 having an extended segment 10a which together with optical sensors 11 and 12 mounted on the inner wall of the upper body of ball valve 3, acts to switch off power to motor 1 when ball valve 3 is fully opened or fully closed. Optical disc 10 and sensors 11, 12 are shown more clearly in figure 4. When segment 10a of optical disk 10 passes between poles of optical sensor 11 or 12 power supply to motor 1 is terminated.

Figure 5 shows two such motor/gearbox/valve assemblies coupled together via a coupling 13 including a mixing chamber 15 and a mixed water outlet 15a.

Figure 6 shows a schematic diagram of a valve mixing device according to one embodiment of the present invention. The latter embodiment utilizes control means realized with relays. The control means includes four control touch sensitive membrane switches/buttons labelled ON, HOT, OFF and COLD respectively, steering diodes 14, 14a and 14b, relays 17, 18 and 19, limit switches 20, 21, 22 and 23 and DC motors 24 and 25. Motors 24, 25 are arranged to drive HOT and COLD water valves 27, 28 respectively.

Power to the mixing device is supplied through a l.OAh sealed lead acid battery 26 which may be recharged using a small 1 watt solar panel (not shown) .

Steering diodes 14, 14a, 14b and relays 17-19 are arranged such that depression of the various switches/buttons causes relays 17-19 and motors 24, 25 to be actuated as follows:

As is evident from the above table depression of the ON button supplies current having a first polarity to both DC motors 24, 25 causing associated valves 27, 28 to open. Release of the ON button stops the current supply. Depression of the OFF button supplies current having a second polarity, opposite to the first polarity, to both motors 24, 25 causing associated valves 27, 28 to close. Release of the OFF button stops the current flow.

Depression of the HOT button supplies current of the first polarity to motor 24 causing hot water valve 27 to open and supplies current of the second polarity to motor 25 causing cold water valve 28 to close. Thus depression, of the HOT button increases the temperature of the water in the mixed water outlet. If water is supplied to hot and cold valves 27, 28 at the same pressure and if valves 27, 28 have substantially linear flow characteristics, depression of the HOT button will not substantially alter pressure of water in the mixed water outlet. Release of the HOT button stops the current flow.

Depression of the COLD button supplies current of the first polarity to motor 25 causing to the cold water valve 28 to open and current of the second polarity to motor 24 causing the HOT water valve 27 to close. Accordingly depression of the COLD button decreases the temperature of the water. Release of the COLD button stops the current flow.

Limit switches 20 and 22 stop current supply to motors 24, 25 when the associated valves are fully opened while limit switches 21 and 23 stop current supply to motors 24, 25 when the associated valves are fully closed.

Figure 7 is a block diagram of a mixing device controlled by a central processing unit (CPU) 29 such as a microprocessor or microcontroller. Power is supplied to the device by l.OAh sealed lead acid battery 30, charged by a 1 watt solar panel 31. CPU 29 accepts input commands via keyboard 32. Keyboard 32 allows an operator to store and recall up to eight sets of temperature/pressure combinations. The desired - pressure/temperature combinations are stored in memory 33. The keyboard includes HOT, COLD, ON and OFF buttons and allows the operator to control the temperature and pressure of the water manually using the HOT, COLD, ON and OFF buttons. The latter buttons may perform the same or similar functions as the buttons described with reference to figure 6 and to set the maximum temperature of the water at the mixed water outlet.

Temperature sensors 34, 35 and 36 monitor the temperatures in the hot water inlet, cold water inlet and mixed water outlet respectively and feed that information back to CPU 29. Pressure sensor 37 located in the mixed water outlet monitors the pressure of the water in the mixed water outlet and feeds that information back to the CPU 29.

By committing to memory 33 a desired temperature/pressure condition CPU 29 can recreate that temperature/pressure condition on command. It does this by monitoring the actual temperature and pressure at the mixed water outlet, comparing the actual temperature and pressure with the desired temperature and pressure and adjusting the hot and cold water valves (not shown) via motors 38 and 39 respectively until the desired temperature and pressure conditions are recreated. The CPU controls the operation of motors 38, 39 via interfaces 40 and 41 and motor drivers 43 and 43a. Each motor driver 43, 43a may comprise a field effect power transistor.

When a desired temperature is realized at the mixed water outlet CPU 29 can monitor, via temperature sensors 34 and 35, any change in temperature of the water at the cold and hot water inlets respectively, and compensate for that change in temperature by making appropriate changes to the valve positions thereby maintaining the desired mixed water temperature. This allows the device to anticipate changes to water temperature before they reach the mixed water outlet and to adjust the valve positions with a more rapid response.

CPU 29 is coupled to an LCD display 42 upon which temperatures, pressures, maximum temperature, memory number etc can be displayed.

CPU 29 is also coupled to a real time clock 43 which is used to run periodical system checks. It is also possible to use the real time clock to display the time on the LCD display 42.

CPU 29 is coupled to a serial port interface 44 alowing interconnection to other motorized valve sets and a reset interface 45 allowing a technician to reset CPU 29 via a reset button associated with reset interface 45.

Figure 8 shows a possible design for a control panel for the mixing device shown in figure 7. Buttons 46, 47,

48 and 49 could be labelled ON, HOT, OFF and COLD respectively or alternatively or additionally the buttons could be color coded, orange, red, black and blue respectively. The control panel includes a liquid crystal display 50, memory recall button 51, memory store button 52, maximum temperature set-up button 53 and maximum temperature set-down button 54.

It is envisaged that the mixing device of the present invention may be fitted as a replacement for manually operated taps. The applications potentially include kitchen sinks, laundry troughs, showers, baths, washing machines and hand basins. They may be installed as original and permanent equipment in houses, shops, hospitals, nursing homes, homes for the disabled, etc.

Finally it is to be understood that various alterations, modifications or additions may be introduced into the taps and mixing devices of the present invention previously described without departing from the spirit or ambit of the invention

Claims

1. A device for mixing water supplied to a common outlet from sources of hot and cold water, said device including: first electrically operable valve means for controlling said supply of cold water to said common outlet; second electrically operable valve means for controlling said supply of hot water to said common outlet; and control means for controlling operation of said first and second valve means whereby temperature of water at said common outlet is continuously adjustable independent of pressure and vice versa.

2. A device according to claim 1 wherein said control means includes first, second, third and fourth switches and is adapted:

upon actuation of said first switch to supply current having a first polarity to said first and second valve means, causing said first and second valve means to open;

upon actuation of said second switch to supply current having a second polarity opposite to said first polarity to the first and second valve means causing said first and second valve means to close;

upon actuation of said third switch to supply current having the first polarity to the first valve means causing said first valve means to open and supply current having the second polarity to said second valve means causing said second valve means to close; and

upon actuation of said fourth switch to supply current having the first polarity to said second valve means causing said second valve means to open and supply current having said second polarity to said first valve means causing said first valve means to close.

3. A device according to claim 2 wherein each sai switch is associated with a respective button, each switc being actuated upon depression of the associated button an being deactuated upon release of the associated button.

4. A device according to claim 1, 2 or 3 wherein sai first and second electrically operable valve means compris respective first and second electric motors coupled t respective first and second water valves.

5. A device according to claim 2, 3 or 4 wherein eac said electric motor is coupled to each said valve via reduction gearbox.

6. A device according to any one of claims 2 to wherein each said electric motor is a reversible DC motor.

7. A device according to any one of claims 2 to wherein each water valve has substantially linear flo characteristics over the range of flow required from sai outlet.

8. A device according to any one of claims 2 to wherein each water valve is opened or closed by rotation o a spindle.

9. A device according to any one of claims 2 to wherein each water valve comprises a stainless steel bal valve including a ball and spindle.

10. A device according to claim 9 wherein each bal includes a slit-shaped orifice.

11. A device according to claim 9 or 10 wherein sai ball and spindle are formed in one piece.

12. A device according to any one of claims 9 to 1 wherein each motor causes the respective spindle of the valve to rotate at a speed between 2 and 5 r.p.m.

13. A device according to any one of claims 9 to 12 wherein the ball valve rotates at least 75° between fully open to fully closed positions.

14. A device according to any one of claims 4 to 13 further including limit switches for interrupting current to the motors when the associated valves are fully opened or fully closed.

15. A device according to claim 1, 2 or 3 wherein each electrically operable valve means comprises a proportional opening solenoid valve.

16. A device according to any one of claims 1 to 15 wherein the control means comprises a plurality of relays and steering diodes.

17. A device according to any one of claims 1 to 15 wherein the control means comprises a central processing unit (CPU) .

18. A device according to claim 17 including temperature and pressure sensors located in said common outlet, wherein the central processing unit monitors temperature and pressure of water in said common outlet via said temperature and pressure sensors.

19. A device according to claim 17 including memory means for storing desired temperature and pressure of water at said common outlet and means, associated with said CPU, for sensing actual temperature and pressure of water at said common outlet wherein said CPU is adapted to compare said desired and actual temperatures and pressures and to automatically adjust said first and second valve means until said desired and actual temperatures and pressures are substantially equal.

20. A device according to claim 19 including respective means, associated with said CPU, for sensing temperature at said sources of said hot and cold water wherein said CPU is adapted to adjust said first and/or second valve means to compensate for changes in temperature of said hot and/or cold water.

21. A device according to any one of claims 17 to 20 including a serial port interface adapted to connect said CPU to at least a further like set of first and second electrically operable valve means, whereby said CPU is adapted to control said further like set.