GB2390135A

GB2390135A - Water flow control device

Info

Publication number: GB2390135A
Application number: GB0214537A
Authority: GB
Inventors: Dominic George Webber; Robin Craig Cocker; Peter Georg Laitenberger; Mark Andrew Thompson; Kelvin Towler
Original assignee: Aqualisa Products Ltd
Current assignee: Aqualisa Products Ltd
Priority date: 2002-06-24
Filing date: 2002-06-24
Publication date: 2003-12-31
Also published as: GB2390141B; GB0314019D0; GB2390141A; GB0214537D0

Abstract

The device 12 may be used in an instantaneous electric water heater such as in a shower and has a water flow inlet 102, outlets 120a and 120b, and a connecting conduit 101. Two orifices 116a and 116b are positioned in the conduit and are defined by respective o-rings 115a and 115b. The cross-sectional area of each orifice is filled by a movable member 110a and 110b. The movable members have a number of grooves 112a and 112b on their outer surface which extend longitudinally and vary in cross-section along their length. The cross-section varies in opposite directions on each movable member. A first flow control part is defined by a space between the o-ring 115a and grooves 112a and a second flow control part is defined by a space between the o-ring 115b and grooves 112b. Movement of the movable members in opposite directions, such as by a pinion 140 and racks 130a and 130b, upstream or downstream of the water flow inlet control the water flow rate through the device.

Description

WATER FLOW CONTROL DEVICE

The present invention relates to a water flow control device, in particular a water flow control device for use in an instantaneous electric water heater for a 5 shower.

A great variety of water flow control devices are known. One type of water flow control device includes an axially moveable "core" surrounded by an o-ring.

Axially extending longitudinal grooves are provided on the periphery of the core and have cross sectional areas which vary along their length. Water flows through the 10 grooves between the core and the o-ring, the cross-sectional area of the grooves at the o-ring determining the flow rate of water. By moving the core longitudinally through the o-ring, the cross-sectional area of each of the longitudinal grooves at the o-ring and the flow rate of water is varied.

The flow control device described above has the problem that a large force 15 may be required to move the core in the direction of the incoming water i.e. when the core is moved upstream. Therefore, it can be difficult to vary the flow rate and substantial mechanisms may be required to enable a user to be able to move the core.

According to the present invention, there is provided a water flow control device comprising: 20 a first orifice and a second orifice; a first moveable member positioned in said first orifice; a second moveable member positioned in said second orifice; an inlet and an outlet; and conduits for defining a water flow path from said inlet towards said first and 25 second orifices and to said outlet; wherein said first and second moveable members are coupled together such that on movement of one of said moveable members in a first direction in said flow path relative to said inlet, the other of said moveable members moves in a second direction in said flow path relative to said inlet, said first and second directions being 30 opposite, and wherein movement of said moveable members is effective to cause a

-2 variation in the flow rate of water through said device.

In this way, the force required to actuate the water flow control device is much reduced. In particular, the pressure of water on the first moveable member is balanced by the pressure of water on the second moveable member i.e. as one moves S upstream the other moves downstream. This is advantageous because, if the water flow control device is manually operated, adjustment of the rate of flow requires little force. This reduction in force also allows tactile feed back for the operator to be provided. If the water flow control device is controlled electronically, it is not necessary to use powerful solenoids or powerful electric motors. These powerful 10 devices are expensive and not particularly reliable.

Preferably, in the water flow control device the first and second moveable members are directly coupled together with a coupling element. This allows a simple and compact design and even allows the first and second moveable members to form part of the same member. In this case, at least one of the first and second moveable 15 members may be tubular and the inside of at least one of the members may define part of the flow path. This arrangement is advantageous as the design of the conduits for deeming a water flow path from the inlet towards the first and second orifices and to said outlet can be sirnplifed.

Preferably, in the water flow control device an actuation means comprises a 20 means for longitudinal displacement of said moveable members.

Preferably, the means for longitudinal displacement is a wax capsule arranged to move said first and second moveable members in response to a change in water temperature in the flow path of water. In this way, the water flow control device may be used as a thermostatic flow control device in an instantaneous electric water heater 25 to thermostatically vary the temperature by either mixing hot and cold water or by varying the flow rate of water through a heater can of the water heater. The wax capsule can be placed either before or after a heater can for heating the water in the electric water heater.

The low force required for actuation of the water flow control device allows a 30 wax capsule to be used as the actuation means.

-3 Preferably, the water flow control device further comprises an actuation means effective for moving the first and second moveable members in the flow path relative to the inlet and the actuation means is a valve in the flow path actuation of which is effective, in use, to cause a force imbalance on the first and second 5 moveable members due to a pressure difference between the pressure of water on the first and second moveable members in the flow path on the side of the inlet, thereby to move the moveable members. In this way, the water flow control device may be controlled by a pilot valve which requires a low force for actuation. The valve may then be controlled by a solenoid and can even be used to shut off completely the 10 water flow through the water flow control device.

In such a water flow control device, preferably the first and second moveable members present different cross sectional areas to the flow path on the side of the inlet. In this way, a predetermined force imbalance between the first moveable member and the second moveable member may be inbuilt into the water flow control 1 S device.

Preferably, in the water flow control device, movement of the moveable members is effective to actuate a switch. In this way, the power supply to other elements of the apparatus in which the water flow control device is used may be actuated at a predetermined flow rate. For example, if the water flow control device 20 is used in an instantaneous water heater, the switch which is actuated by movement of the moveable members could be the main switch for the power supply to heater elements of the instantaneous electric water heater.

Preferably, in a water flow control device, a flow control part of the flow path is defined between the first and second moveable members and the first and second 25 orifices respectively. In this way, movement of the first and second moveable members relative to the first and second orifices can result in variation of the water flow rate through the water flow control device.

The present invention further provides a method of controlling water flow rate in a flow path between an input and an output, said method comprising the steps 30 of:

-4 arranging for said flow path to have a first path section from said input to a first orifice and a second path section from said input to a second orifice; directing water coming through said first and second orifices to said output; and 5 moving a first moveable member positioned in said first orifice and a second moveable member positioned in said second orifice in opposite directions in said flow path relative to said inlet thereby to cause a variation in the flow rate of water through said first and second orifices.

In this way, the force required to move the moveable members against the 10 pressure of water in the inlet is reduced. This is because when one moveable member moves against the pressure on the inlet side, the other moveable member moves in the direction of the force from the pressure on the inlet side. Thus, if the moveable members are coupled, to transfer forces between each other, the forces on the members during movement are balanced and adjustment of the flow rate can 15 easily be achieved.

The invention will be more clearly understood from the following description, given by way of example only, with reference to the accompanying

drawings, in which: Figure 1 illustrates the front cover of an instantaneous water heater; 20 Figure 2 illustrates an exploded view of functional components of an instantaneous water heater; Figure 3 illustrates a cross sectional view of a first embodiment of a water flow control device; Figure 4 illustrates a cross sectional view of a second embodiment of water 25 flow control device; Figure 5 illustrates a cross sectional view of a third embodiment of a water flow control device; Figure 6 illustrates a cross sectional view of a fourth embodiment of water flow control device; 30 Figure illustrates a cross-sectional view of a fifth embodiment of water flow

-s - control device; and Figure 8 illustrates a cross-sectional view of a sixth embodiment of a water flow control device.

As illustrated in Figure 1, an instantaneous water heater includes a front cover 5 2 including a water temperature control 4 and an optional on/off button 6. As will be described below, the function of the on/off button 6 may also be incorporated into the temperature control 4.

The front cover 2 houses a number of functional components for providing hot water of a desired temperature.

10 Figure 2 illustrates a suitable arrangement of components. However, it should be appreciated that many other arrangements could be provided within the scope of the invention.

Water is provided to one of two alternative inlets 8 and 10. With the water heater running, the water is then channelled via a flow rate control device 12 to the 1 S inside of a heater can 14. Within the heater can 14, the water flows up around the outside of a chimney 16 in contact with a heater element 18. The water then flows down through the inside of the chimney 16 and out of an outlet 19.

In the embodiment illustrated in Figure 2, an on/off flow control valve 20 operates under the control of a button 22a to control whether or not there is any flow 20 from the inlets 8 or 10 to the water flow control device 12. Dependent upon the position of the on/off control valve 20 and/or flow of water through the water heater, an arm 24 operates an electrical switch 26 to turn on or off power to the heater element 18. As will be seen below, the function of the water flow control device 12 and the on/off control valve 20 can be incorporated into a single flow control device.

25 The water flow control device t 2 may be operated by a rotatable member 28 so as to vary the water flow rate through the heater can 14 and hence the water temperature at outlet 19.

Figure 3 illustrates a water flow control device 12 suitable for use with the instantaneous electric water heater of Figure 2. The water flow control device 12 30 comprises an inlet 102 for the flow of water into the water flow control device 12 and

-6 an outlet which, in the illustrated embodiment, is formed from two separate pipe openings 120a and 120b.

First and second o-rings 115a and 115b define respectively first and second orifices 116a, 116b on their inner sides. Positioned in the first and second orifices 5 116a, 116b are first and second moveable members l lea, l lab respectively. The moveable members 11 Oa, 11 Ob have crosssections which generally match the inner cross-sections of the respective orifices. As illustrated, they are in the form of cylindrical cores. However, other shapes may also be used such as cones.

Conduit 101 defines a flow path from the inlet 102 to the outlet formed of the 10 two openings 120a, 120b such that water flows from the inlet towards and then through the first and second orifices 116a, 116b and then on to the outlet 120a, 120b.

The outer surface of the cores are formed with a plurality of grooves 112a, 112b which extend longitudinally in the direction of travel of the cores and which vary in cross section along their longitudinal length. The cross section of the 15 longitudinal grooves 112a, 112b on the first and second cores l lea, l lOb varies in opposite directions. On the first moveable member 11 Oa, the longitudinal grooves 112a increase in cross sectional area in the direction from the inlet 102 to the outlet 120a. On the second moveable member 11 Ob, the longitudinal grooves 112b decrease in cross sectional area in the direction from the inlet 102 to the outlet 120b.

20 The space between the first o-ring 115a and the grooves 112a in the first moveable member l l Oa define a first flow control part. The overall cross sectional area of the first flow control part (i.e. the sum of the cross-sectional areas of the longitudinal grooves 112a at the o- ring 11 Sa) may be varied by moving the position of the first moveable member 11 Oa in the flow path relative to the first o-ring 115a 25 towards or away from the inlet 102, i.e. upstream or downstream. Movement of the first moveable member 11 Oa towards the inlet 102 (i.e. upstream or towards the high pressure side) will increase the cross sectional area of the flow control part. In this way water will flow more easily between the first o-ring 115a and the first moveable member 11 Oa thereby increasing the flow rate of water through the flow control 30 device 12. Thus, the cross sectional area of the grooves 112a at the o-ring 115a

-7 defines a first flow control part of the device.

A second flow control part of the device is deemed by the grooves 112b of the second core 11 Ob and the second o-ring 115b. The second o-ring 115b interacts with the second moveable member l lob in the same way as the first o-ring l 15a interacts 5 with the first moveable member l lea. However, the longitudinal grooves 112b of the second moveable member l lab have an opposite orientation to the longitudinal grooves 112a of the first moveable member 11 Oa. Therefore, movement of the second moveable member 11 Ob towards the outlet 120b (i.e. downstream or towards the low pressure side) has the effect of increasing the flow rate of water through the 10 flow control device 12.

Moving either ofthe moveable members l lea, l lob towards the inlet 102 away from the outlet 120a, 120b (i.e. upstream) requires a larger force than moving them away from the inlet 102 towards the outlet 120a, 120b (i. e. downstream). This is because the upstream water pressure is higher than the downstream water pressure.

15 By arranging for the first and second moveable members 11 Oa, 11 Ob to move in opposite directions relative to the inlet 102, and hence the flow of water, the force required to vary the cross sectional area of the flow control device is much reduced.

Thus, as illistrated, the first and second moveable members 11 Oa, 11 Ob are coupled such that movement of one of the moveable members l lea, l lob in a first direction 20 in the flow path relative to the inlet 102 causes the other of the moveable members 11 Oa, 11 Ob to move in a second direction in the flow path relative to inlet 102, the first and second directions being opposite.

In the first embodiment illustrated in Figure 3, a coupling is provided which includes first and second racks 130a, 130b attached to the first and second moveable 25 members 11 Oa, 11 Ob respectively. A pinion 140 is coupled with both of the first and second racks 130a, 130b. It is effective to co-operate with the first and second rack 13 Oa, 130b such that rotation of the pinion 140 results in movement of the first and second moveable members 11 Oa, 11 Ob in opposite directions in the first and second orifices 116a, 116b relative to the irdet 102.

30 In an instantaneous water heater, one way of controlling the temperature of

-8 the water at the outlet is to control the flow rate of water through the heater can, thereby varying the amount of time which the heater can has to heat the water.

The device of Figure 3 may be incorporated into the heater of Figure 2 by connecting the output of the on/off control valve 20 to the input 102 and by 5 connecting the outputs 120a, 120b to the heater can. The pinion 140 may then be coupled to the rotatable member 28 of the instantaneous water heater illustrated in Figure 2 so that it may be operated manually through the water temperature control 4 of Figure 1 to select a desired water temperature.

The pinion 140 may alternatively be controlled by an electric motor and 10 associated electrical circuitry. The power of the electric motor assigned to such a task will be small compared to the electric motor required for previous water flow control devices which are not balanced with respect to the pressure of water in the inlet 102.

Figure 4 illustrates a second embodiment of a flow control device. This could 15 also be used in the electric instantaneous water heater of Figure 2 with minor modifications of the conduits 201 for compatibility with the other components of the instantaneous electric water heater of Figure 2. The functioning of the second embodiment is generally the same as that of the first embodiment. More important differences are described below.

20 In the embodiment illustrated in Figure 4, conduits define a flow path from an inlet 202 to an outlet formed from two openings 220a, 220b and first and second orifices are defined by wrings 215a and 215b. First and second moveable members 210a, 21 Ob are positioned in the first and second orifices and the flow control part of the flow control device of Figure 4 is defined by the cross sectional area between the 25 first o- ring 215a and the first moveable member 210a and between the second o- ring 215b and the second moveable member 210b.

In the embodiment in Figure 4, the first and second moveable members 21 Oa, 210b are coupled directly together with an element 230. The element 230 attaches the members 21 Oa, 21 Ob to one another with a fixed spacing. It is stiff or rigid so as 30 to resist generally any compression or expansion. As illustrated, the element 230 is a

-9- rack which is driven by a pinion 240. Driving of the rack 230 by the pinion 240 results in movement of the first and second moveable members 210a, 210b in opposite directions relative to the inlet 202. Thus, in this embodiment, since the moveable members are attached together and driven by the same rack, they are both 5 moved in the same actual direction. However, the flow path defined by the conduits causes water to flow from the inlet past the moveable members in opposite actual directions. In this way, this moveable members still move in opposite directions relative to the inlet and the flow of water from the inlet.

Figure 5 illustrates a third embodiment of a flow control device. This is also 10 suitable for use in the instantaneous electric water heater illustrated in Figure 2. The functioning of the third embodiment is the same as that of the first embodiment save as described below. In the third embodiment, conduits 301 define a flow path from an inlet 302 to an outlet formed from two openings 320a, 320b. The flow path is formed such that the required movement of first and second moveable members 1 3 l 5a, 315b does not need to be at least partly accomplished by rotational movement but can be accomplished solely by linear movement.

The first and second moveable members 315a, 315b are directly coupled together with an element 331. As illustrated, the element 331 attaches the moveable members 315a, 315b together in a direction generally perpendicular to their direction 20 of travel. Therefore, the element as preferably stiff or rigid to withstand bending.

The element 331 may be moved by an actuation means which comprises a means for longitudinal displacement of the moveable members 315a, 315b. Such a means for longitudinal displacement may be a wax capsule (not illustrated) which is placed in the flow path of the flow control device or elsewhere, for example in the outlet 19 of 25 the instantaneous electric water heater.

The wax capsule will expand or contract depending on the temperature of the water surrounding the wax capsule. By coupling the wax capsule to the element 331 the setting of the water flow control device may be varied according to the temperature of the wax capsule. By placing the wax capsule either in the water flow 30 path before or after the heater can 14, the water flow control device may be used in a

-10 therrnostatic way, in particular varying the flow rate of water through the heater can 14 according to the temperature (and therefore length) of the wax capsule. In particular, the wax capsule may be used to vary the flow rate so as to compensate for variations in inlet water temperature so as to maintain a constant heated outlet 5 temperature.

Of course, the water flow control device of Figure 5 may also be used with a manual control by placing, for example, a rack on the element 331 and provides a pinion to drive the rack. Similarly, the arrangement of Figure 4 could be driven with a wax capsule as described above.

10 A fourth embodiment of water flow control device is illustrated in Figure 6.

The device of Figure 6 has the particular advantage that it is compact. The functionality of the fourth embodiment is the same as the first embodiment save as described below. It can also be considered as similar to the second embodiment without the use of the connecting element.

15 In the fourth embodiment, the first and second moveable members 410a, 41 Ob are part of the same member and hence, may be formed integrally. In the illustrated embodiment, the moveable member 410 is tubular and the inside 411 of the member 410 defines part of the flow path for the water. First and second Wrings 41 5a, 41 Sb are associated with each of the first and second moveable members 41 Oa, 20 41 Ob. The outlet 420 of the fourth embodiment is positioned at the periphery and may be at least partly annular.

The moveable members 41 Oa, 410b of the fourth embodiment may be actuated in any way known in the art or as described herein.

The embodiment is particularly suitable for use with a wax capsule so as to 25 provide means for allowing thermostatic control of the flow rate of water. In the illustrated embodiment the wax capsule could conveniently be placed on the inlet side 402 of the moveable member in the flow path. Thus, the flow rate could be controlled according to the inlet temperature of the water.

It should be appreciated that, instead of a hollow moveable member, the inlet 30 water flow can be split and fed separately to each end of the moveable members.

- 1 1 However, with a hollow moveable member the amount of conduit 401 required for defining the flow path can be reduced as otherwise two inlets rather than just a first inlet 402 would be required.

The idea of using hollow moveable members can also be applied to other 5 embodiments of the present invention even where the first and second moveable members are not part of the same member.

The fifth and sixth embodiments of the present invention as illustrated in Figures 7 and 8 each use, as an actuation means, a valve in the flow path of the device. Actuation of the valve is effective to cause a force imbalance on the first and 10 second moveable members due to a pressure difference between the pressure of water on the first and second moveable members in the flow path on the side of the inlet.

The force imbalance is high enough to move the moveable members.

Each of the devices of the fifth and sixth embodiments can be used not only to control the flow rate of water through the device but also to completely shut off 15 the flow of water through the device. Thus, the devices of the fifth and sixth embodiments can replace both the flow control device 12 of the instantaneous electric water heater of Figure 2 as well as the on/off control valve 20.

The advantage of the flow control devices of the fifth and sixth embodiments is that use is made of a pressure difference on the inlet side of the first and second 20 moveable members to control the position of the moveable members i.e. they are servo controlled valves. In this way, the pressure of water on the inlet side of the devices can be used to set the position of the moveable member and thereby change the flow rate. In this way only a small force is required to control the position of the moveable member from either the user or from an electrical transducer.

25 The water flow control device of the fifth embodiment comprises a first moveable member 51 Oa (control core) which is integrally formed with a second moveable member 510b. The functionality of the fifth embodiment is the same as that of the first embodiment save as described below.

The cross sectional area of the first moveable member 51 Oa presented to the 30 water inlet 502 perpendicular to the direction of movement of the first and second

-12 cores S 1 Oa, 51 Ob is larger than the corresponding cross sectional area of the second moveable member 51 Ob. This is chosen so as to ensure that the force from the water pressure in the inlet 502 is greater on the first core 520a than on the second core S 1 Ob if those cores are exposed to the same water pressure in the inlet 502.

5 A valve 550 positioned between the water inlet 502 and the first moveable member S lea (but not the second moveable member 512b) controls the difference in water pressure between the inlet 502 and the area adjacent the first moveable member S 1 Oa. The valve SSO may be a needle valve or a pilot valve such that it may operate with minimal displacement and/or force so that a bi-metallic strip, a wax capsule or a 10 small electrical transducer can be used to control the area of the opening of the valve.

The flow control device of the fifth embodiment also comprises a valve plate 540 which is biased (by a spring 545) against a valve o-ring 542. When the valve plate 540 lies on the valve o-ring 542 the path of water from inlet 502 to the second moveable member 512b is blocked.

IS The second moveable member 512b can be moved towards the inlet 502 (i. e. upstream and rightwards as illustrated) to contact with the valve plate 540. Further movement to the right as illustrated of the second moveable member 510b is effective to lift the valve plate 540 from the valve o-ring 542 and thereby to open the flow path from the inlet 502 to the second moveable member 510b.

20 The first moveable member SlOa is also attached to an actuating rod 565.

Movement of the first moveable member 510a away from the direction of the inlet 502 (i.e. downstream and to the right as illustrated) is effective for the actuation rod 565 to actuate a switch 560.

When the flow control device of the fifth embodiment is used in an 25 instantaneous electric water hater, the flow control device can eliminate the need for an on/off button 6 as actuation of the valve 550 to move the moveable members to the right (as illustrated) is effective to control the on/off switch 560 for current to the heating elements 18 of the heater can 14.

The control valve 20 is also eliminated as when valve 550 is closed the 30 second moveable member 510b moves away from the inlet 502 (i.e. upstream and

-13 leftwards as illustrated) as a result of the biasing of spring 545 and increase in pressure on the outlet 520 side (i.e. downstream). In this scenario the valve plate 540 settles on the valve o-ring 542 to seal the path for water between inlet 502 and the second moveable member 510b. The path for water from the inlet 502 to the first 5 moveable member 51 Oa is blocked by the valve 550. Therefore, the flow control device of the fifth embodiment may be used to completely block off the flow of water thereby eliminating the need for the control valve 20.

The operation of the flow control device of the fifth embodiment will now be described. When the valve 550 is closed, the pressure of water on the upstream side 10 of the first moveable member 51 Oa is less than the pressure on the upstream side of the second moveable member 51 Ob if the valve plate 540 is off of the valve o-ring 542. in this case, the upstream force of water on the second moveable member 51 Ob due to the water pressure in the inlet 502 is such that the first and second moveable members 51 Oa, 51 Ob will move to the left as illustrated (towards the inlet i.e. 15 upstream for the first moveable member 51 Oa and away from the inlet i.e. downstream for the second moveable member 51 Ob) until the valve plate 540 settles on the valve o-ring 542. In this position neither the first nor the second moveable members 510a, 510b experience pressure from water from the inlet 502. Thus, there is no overall force on themoveable members 51 Oa, 51 Ob and as neither of the flow 20 control paths of the first and second moveable members are exposed to water pressure from the inlet 502, no water flow results.

On partial opening of the valve 550 the water pressure on the inlet side (i.e. upstream) of the first moveable member 51 Oa increases such that there is a net overall force on the moveable members 51 Oa, 51 Ob towards the right as illustrated.

25 This has the effect of increasing the flow rate through the flow control part of the first moveable member 51 Oa as longitudinal grooves 512a in the first member 51 Oa increase in cross sectional area towards the inlet 502. The movement also has the effect of resulting in the valve plate 540 being lifted off the valve seat presented by valve o-rings 542 thereby exposing the second moveable member 51 Ob to the inlet 30 502.

-14 At this stage, the position of the first and second moveable members 51 Oa, 51 Ob will be determined by an equalling of the forces from water pressure on the first and second moveable members 510a, 510b and on the force of the biasing spring 545 on the second moveable member 510b. As the cross-sectional area exposed to the 5 water pressure of the first moveable member 51 Oa is larger than that of the second moveable member 51 Ob, a smaller pressure on the inlet side of the first moveable member S l Oa is required than that pressure on the inlet side of the second moveable member 512b to hold the moveable members in equilibrium.

The initial opening of the flow control device described above also results in 10 the actuation of the switch 560 by the actuation rod S65.

In the open position resulting from valve S50 being at least partly opened, water flows both through the flow control path of the first and second moveable members 51 Oa, S l Ob as defined by the longitudinal grooves 512a, 512b. The longitudinal grooves 512b have a cross sectional area which decreases before 1 S increasing on movement of the second moveable member 51 Ob from one extreme displacement in the flow path relative to the input 502 to the other extreme. In this way, the flow rate just before the flow rate is reduced to zero is closed is increased.

This is a safety feature which ensures that when the instantaneous electric water heater is being shut off sufficient water is in the heater can 14 to avoid boiling of 20 water in the heater can 14 (boiling can occur if the flow rate of water through the can is not high enough).

The amount of displacement of the moveable members 510a, 510b to the right as illustrated (i.e. an increasing flow rate after the initial fall described above) can be varied by opening or closing valve 550. Opening the valve 550 will increase 25 the pressure of the water on the inlet side of the first moveable member 51 Oa thereby resulting in movement towards the right of both of the moveable members 51 Oa, 51 Ob because of the larger cross sectional area of the first member 51 Oa compared to the second member 51 Ob exposed to the pressure of water from the inlet 502.

On closing of the valve 550 the pressure on the inlet side of the first 30 moveable member 510a decreases whilst the pressure on the second moveable

-15 member SlOb on the inlet side remains substantially the same. This serves to generate an overall force to the left as illustrated on the first and second moveable members 510a, 510b. Thus, the first and second moveable members 510a, 510b move to the left until the valve plate 540 shuts off the second moveable member 5 510b from the inlet 502 by contacting with the valve seat 542.

The flow of water past the (control) first moveable number 510a is kept as low as possible (by making grooves 512a very thin and by ensuring the majority of the flow goes past the second moveable member 510b in the grooves 512b) so that only a small force is required to actuate the pilot valve 550 as only little flow passes 10 through that part of the system. This is in contrast to the sixth embodiment in which all flow must go through the valve equivalent to the pilot valve 550 of the fifth embodiment. The sixth embodiment illustrated in Figure 8 is the same as that of the fifth embodiment illustrated in Figure 7 save as described below. In the sixth embodiment 15 the diameters of the first and second moveable members 610a, 610b is the same. The device works because of the biasing of the moveable members by spring 645 which acts on the moveable members via a extension member 640 attached to the moveable member 610a, 61 Ob. The second moveable member 610b does not have any longitudinal grooves such that the only flow control part of the device is defined as 20 the sum of cross sectional areas of the grooves 612a at the first oring 615a. This cross sectional area can be varied because the longitudinal grooves 612a which have a varying cross sectional area along the longitudinal length of the first moveable member 610a.

As in the fifth embodiment, the position of the first and second moveable 25 members 61 Oa, 61 Ob is controlled by the pressure difference on the inlet side of the first and second moveable members 610a, 610b. The pressure on the first moveable member 61 Oa from water from the inlet 602 is controlled by a pilot valve 650.

The pilot valve 650 comprises a valve member 651 and a valve seat 652. By varying the flow rate of water through the pilot valve 650 the position of the 30 moveable members 610a, 610b can be varied and so thereby can the cross sectional

-16 area of the flow control part of the control device. As in the fifth embodiment, the energy needed to operate the pilot valve 650 may be lower because of the use of the pressure of the water in the inlet 602 being used to vary the position of the cross sectional members. This is possible because the cross sectional members move in 5 opposite directions in the flow path relative to the inlet 602 thereby balancing the forces in both directions.

There are several further advantages of the fifth and sixth embodiments relating to automatic positional adjustment of the moveable members 510a, 510b, 610a, 610b on pressure variation in the flow path. For example in the fifth 10 embodiment if the water pressure at the inlet 502 decreases to below a predetermined value which is governed by the stiffness of the spring 545, the moveable members 510a, 510b will automatically be moved to the left as illustrated thereby switching switch 560 off and so automatically preventing the heater elements 18 from boiling the little remaining water flowing through the flow control valve. In a similar way, if 15 the water pressure builds up downstream of the moveable members 51 Oa, 51 Ob at outlet 520, due to, for example, blockage of a shower head to which the instantaneous water heater is connected, the moveable members 510a, 510b will move to the left as illustrated thereby to stop power to the elements 18.

The fifth and sixth embodiments can also provide automatic regulation of 20 position of the first and second moveable members on variation of water pressure at the inlet 502, 602 to keep the flow rate through the valve substantially constant. As pressure increases at the inlet 502, a similar increase occurs upstream of the first moveable member 51 Oa and so the flow rate will increase. As the flow rate increases the pressure drop across the pilot valve 550 will increase leading to a reduction in 25 pressure upstream of the first moveable member 51 Oa so that the moveable members 510a, 510b move to the left as illustrated. This leads in turn to a reduction in the cross sectional area available between the o-rings and cores for flow.

The invention has been described with reference to o-rings around the orifices. Actually the invention works without these o-rings as the accuracy of the 30 grooved area is not that important. Further, lip seals (seals with an inward facing

-17 triangular cross-section) have been found to work well as the thin part of the triangle does not squeeze into the grooves which is what can happen with o-rings which can make moving the moveable members hard. Other types of seal may also be used.

Equally, the cores used to illustrate the invention may have other forms. For 5 example the moveable members may be needle valves or the cores may have only one groove.

Claims

-18 CLAIMS

1. A water flow control device comprising: 5 a first orifice and a second orifice; a first moveable member positioned in said first orifice; a second moveable member positioned in said second orifice; an inlet and an outlet; and conduits for defining a water flow path from said inlet towards said first and 10 second orifices and to said outlet; wherein said first and second moveable members are coupled together such that on movement of one of said moveable members in a first direction in said flow path relative to said inlet, the other of said moveable members moves in a second direction in said flow path relative to said inlet, said first and second directions being 15 opposite, and wherein movement of said moveable members is effective to cause a variation in the flow rate of water through said device.

2. A water flow control device according to claim 1, further comprising: actuation means effective for moving said first and second moveable 20 members in said flow path relative to said inlet.

3. A water flow control device according to any one of the preceding claims, wherein at least one of said first and second moveable members is tubular and the inside of said at least one member defines part of said flow path.

4. A water flow control device according to claim 2 or 3, wherein said first and second moveable members are directly coupled together with a coupling element.

5. A water flow control device according to claim 2 or 3, wherein said first and 30 second moveable members are part of the same member.

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6. A water flow control device according to claim 3, 4 or 5, wherein said actuation means comprises a means for longitudinal displacement of said moveable members. 5

7. A water flow control device according to claim 6, wherein said means for longitudinal displacement is a wax capsule arranged to move said first and second moveable members in response to a change in water temperature in said flow path.

8. A water flow control device according to claim 2 or 3, wherein said actuation 10 means comprises: a first rack attached to said first moveable member; a second rack attached to said second moveable member; and a pinion disposed between said first rack and said second rack for driving said first and second racks.

9. A water flow control device according to claim 2 or 3, wherein said actuation means comprises a rack connected between said first and second moveable members and a pinion for driving said rack, said first and second moveable members being movable along the same axis.

10. A water flow control device according to claim 2 or 3, wherein said first moveable member and said second moveable member are connected with a connection member, and said actuation means comprises a rack attached to said connection member, said rack being driven by a pinion to move said first and second 25 moveable members along different but parallel axes.

1 1. A water flow control device according to any one of claims 8 to 10, wherein said pinion is attached to a knob such that a user may adjust the position of the first and second moveable members relative to the first and second orifices by horning the 30 knob.

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12. A water flow control device according to any one of claims 8 to 10, wherein said pinion is attached to an electric motor.

13. A water flow control device according to claim 2, wherein said actuation 5 means is a valve in said flow path, actuation of which is effective, in use, to cause a force imbalance on said first and second moveable members due to a pressure difference between the pressure of water on said first and second moveable members in said flow path on the side of said inlet.

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14. A water flow control device according to claim 13, wherein said first and second moveable members present different cross sectional areas to said flow path on the side of said inlet.

15. A water flow control device according to claim 13 or 14, wherein said 15 moveable members are each biased in opposite directions in said flow path relative to said inlet.

16. A water flow control device according to claim 13, 14 or 15, wherein movement of said moveable members is effective to actuate a switch.

17. A water flow control device according to any one of claims 13 to 16, wherein said valve is effective to vary the cross sectional area of said flow path between said first moveable member and said inlet.

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18. A water flow control device according to any one of claims 13 to 17, further comprising a plate biased towards a valve seat, contact of said plate with said valve seat blocking said flow path between one of said moveable members and said inlet, wherein said one of said moveable members is positionable to hold said plate off said valve seat by coupling with said plate.

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l9. A water flow control device according to any one of the preceding claims, wherein a flow control part of said flow path is defined between said first and second moveable members and said first and second orifices respectively.

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20. A water flow control device according to claim l 9, wherein the cross sectional area of said flow control part of said flow path is variable by movement of said moveable members in said first and second directions, thereby, in use, varying the flow rate of water along said flow path.

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21. A device according to claim l 9 or 20, wherein at least one of said first and second moveable members is cylindrical with an outer surface cooperative with an inner surface of said respective first or second orifice.

22. A device according to any one of claims 19 to 21, wherein a plurality of 15 circumferentially spaced longitudinal grooves are present in the outer surface of at least one of said first and second moveable members, said longitudinal grooves having a varying cross section along their length.

23. A device according to claim 22, wherein said circumferentially spaced 20 longitudinal grooves are tapered grooves increasing in size along their length.

24. A water flow control device according to any one of claims 19 to 22, wherein the cross section of said flow control part of said flow path is varied to decrease and then to increase on movement of said moveable members from one extreme 25 displacement in said flow path from said input to the other.

25. A device according to any one of the preceding claims, wherein at least one of said first and second moveable members is tapered in the longitudinal direction such that said moveable member only has one axis of symmetry.

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26. A device according to any one of the preceding cIaims, wherein at least one of said first and second orifices are defined by annular orings.

27. An instantaneous water heater comprising a water flow control device 5 according to any one of the preceding claims.

28. A method of controlling water flow rate in a flow path between an input and an output, said method comprising the steps of: arranging for said flow path to have a first path section from said input to a 10 first orifice and a second path section from said input to a second orifice; directing water coming through said first and second orifices to said output; and moving a first moveable member positioned in said first orifice and a second moveable member positioned in said second orifice in opposite directions in said 15 flow path relative to said inlet thereby to cause a variation in the flow rate of water through said first and second orifices.

29. A water flow control device substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

30. An instantaneous water heater substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

31. A method substantially as hereinbefore described with reference to and as 25 illustrated in the accompanying drawings.