GB2390141A

GB2390141A - Water flow control device

Info

Publication number: GB2390141A
Application number: GB0314019A
Authority: GB
Inventors: Mark Andrew Thompson; Kelvin Towler; Dominic George Webber; Robin Craig Cocker; Peter Georg Laitenberger
Original assignee: Aqualisa Products Ltd
Current assignee: Aqualisa Products Ltd
Priority date: 2002-06-24
Filing date: 2003-06-17
Publication date: 2003-12-31
Anticipated expiration: 2023-06-17
Also published as: GB0314019D0; GB0214537D0; GB2390141B; GB2390135A

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

23901 41

-1 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 shower. 5 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 grooves between the core and the o-ring, the cross-sectional area of the grooves at the I O 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 Me o-ring and the flow rate of water is varied. Single cores need strong and large support mechanisms to hold them in place because the force needed to hold or move them against the pressure of water can be quite high.

15 The flow control device described above has the problem that a large force 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 20 device comprising 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 25 conduits for defining a water flow path from said inlet towards said first and 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

-2 direction in said flow path relative to said inlet, said first and second directions being opposite, and wherein movement of said moveable members is effective to cause a variation in the flow rate of water through said device.

In this way, the force required to actuate the water flow control device is 5 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 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 10 provided If the water flow control device is controlled electronically, it is not necessary to use powerful solenoids or powerful electric motors. These powerful 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 15 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 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 defining a water flow path from the inlet towards the first and second orifices and 20 to said outlet can be simplified.

Preferably, in the water flow control device an actuation means comprises a 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 25 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 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 30 electric water heater.

-3 The low force required for actuation of the water flow control device allows a wax capsule to be used as the actuation means.

Preferably, the water flow control device further comprises an actuation means effective for moving the first and second moveable members in the flow path 5 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 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 10 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 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 15 inlet. In this way, a predetermined force imbalance between the first moveable member arid the second moveable member may be inbuilt into the water flow control 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 20 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 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.

25 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 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.

30 The present invention farther provides 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 first orifice and a second path section from said input to a second orifice; 5 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 flow path relative to said inlet thereby to cause a variation in the flow rate of water 10 through said first and second orifices In this way, the force required to move the moveable members against the 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 15 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 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

20 drawings, in which Figure 1 illustrates the front cover of an instantaneous water heater, 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 25 flow control device; Figure 4 illustrates a cross sectional view of a second embodiment of water flow control device, Figure 5 illustrates a cross sectional view of a third embodiment of a water flow control device; 30 Figure 6 illustrates a cross sectional view of a fourth embodiment of water

-5 flow control device; Figure 7 illustrates a cross-sectional view of a fifth embodiment of water flow control device; Figure 8 illustrates a cross-sectional view of a sixth embodiment of a water 5 flow control device; Figure 9 illustrates, in cross-section, a commercial use of the devices of the first and fourth embodiments; and Figure 10 is an exploded perspective view of a commercial use of a device of the fourth embodiment.

10 As illustrated in Figure 1' an instantaneous water heater includes a front cover 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 15 hot water of a desired temperature.

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 20 heater running, the water is then channelled via a flow rate control device 12 to the 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 ontoff flow control valve 20 25 operates under the control of a button 22a to control whether or not there is any flow from the inlets 8 or 10 to the water flow control device 12. The button 22a may actually control a pilot valve which in turn operates main valve 20 Dependent upon the flow of water through the water heater, an arm 24 operates one or more electrical switches 26 to turn on or off power to the heater element 18. As will be seen below, 30 the function of the water flow control device 12 and the ontoff control valve 20 can

-6 be incorporated into a single flow control device.

The water flow control device 12 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 5 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 comprises an inlet 102 for the flow of water into the water flow control device 12 and an outlet which, in the illustrated embodiment, is formed from two separate pipe openings 120a and 120b.

l O 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 116a, 116b are first and second moveable members 1 lea, 1 lOb respectively. The moveable members l lea, l lob have crosssections which generally match the inner cross-sections of the respective orifices. As illustrated, they are substantially shaped 15 as cylindrical cores optionally formed with surface indented patterns such as grooves described below However, other shapes may also be used such as truncated cones which may also have surface patterns.

Conduit 101 defines a flow path from the inlet 102 to the outlet formed of the two openings 120a, 120b such that water flows from the inlet towards and then 20 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 sectional area along their longitudinal length. The cross section of the longitudinal grooves 112a, 112b on the first and second cores l lea, l lOb varies in 25 opposite directions On the first moveable member l lea, the longitudinal grooves 112a increase in cross sectional area in the direction Tom 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 The space between the first o-ring 11 Sa and the first moveable member 11 Oa 30 defines a first flow control part. The overall cross sectional area of the first flow

-7 control part (i.e. the sum of the cross-sectional areas of the longitudinal grooves 112a at the o-ring 115a and the space between the oring 11 Sa and the surface of the moveable member 110a) may be varied by moving the position of the first moveable member l lea in the flow path relative to the first o-ring 115a towards or away from 5 the inlet 102, i e. upstream or downstream. Movement of the first moveable member l lea 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 device 12. Thus, 10 the cross sectional area of the grooves 112a at the o-ring 115a and the gap between the o-ring and the surface of the moveable member 110a (which gap may not exist i.e. the surface of the moveable member 11 Oa touches the o-ring 11 Sa at all positions except at the grooves 112a) defines a first flow control part of the device.

A second flow control part of the device is defined by the surface of the 15 second moveable member 11 Ob and the grooves 112b of the second moveable member 11 Ob and the second o-ring 115b. The second o-ring 115b interacts with the second moveable member 11 Ob in the same way as the first o-ring l l S a interacts with the first moveable member l lea. However, the longitudinal grooves 112b of the second moveable member 11 Ob have an opposite orientation to the longitudinal 20 grooves 112a of the first moveable member 11Oa as does any change in overall shape along the longitudinal length. Therefore, movement of the second moveable member 110b 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 flow control device 12.

Moving either of the moveable members 110a, l lOb towards the inlet 102 25 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.

By arranging for the first and second moveable members I lOa7 110b to move in opposite directions relative to the inlet 102, and hence the flow of water, the force 30 required to vary the cross sectional area of the flow control device is much reduced.

-8 Thus, as illustrated7 the frst and second moveable members 110a, 110b are coupled such that movement of one of the moveable members 110a, 110b in a first direction in the flow path relative to the inlet 102 causes the other of the moveable members 110a, 110b to move in a second direction in the flow path relative to Inlet 102, the 5 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 members I 1 Oa, I I 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 10 130a, 130b such that rotation of the pinion 140 results in movement of the first and second moveable members 110a, 110b in opposite directions in the first and second orifices 116a, 116b relative to the inlet 102.

In an instantaneous water heater, one way of controlling the temperature of the water at the outlet is to control the flow rate of water through the heater can, 15 thereby varying the amount of time which the heater can has to heat the water.

The device of Figure 3, and for that matter the device of any embodiment, may act as an on/off valve as well as a flow control valve with a simple modification which blocks the orifice at one extreme end of motion of the moveable members.

One such arrangement involves providing one end portion of the circumferential 20 surface of the members with an ungrooved surface of constant cross-section which fits snugly inside the o-ring so that no water can flow between the o-ring and the moveable member when the ungrooved end portion of the circumferential surface is inside the o-ring. Alternatively, the flow path may be blocked by moving the members to a position where end surfaces of the members (that is top and bottom 25 surfaces not being the circumferential surface) bear on a seal other than the o-ring.

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 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 30 Figure 2 so that it may be operated manually through the water temperature control 4

-9- of Figure 1 to select a desired water temperature.

The pinion 140 may alternatively be controlled by an electric motor and 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 5 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 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 I O 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.

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 15 orifices are defined by o-rings 21 Sa and 21 Sb. 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 first oring 215a and the first moveable member 210a and between the second oring 215b and the second moveable member 21 Ob.

20 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 210a, 210b to one another with a fixed spacing. It is stiff or rigid so as to resist generally any compression or expansion. As illustrated, the element 230 is a rack which is driven by a pinion 240 Driving of the rack 230 by the pinion 240 25 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 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 30 directions In this way, this moveable members still move in opposite directions

-10 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 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 S 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 3 l Sa, 31 Sb does not need to be at least partly accomplished by rotational movement but can be accomplished solely by linear movement.

10 The first and second moveable members 3 lSa' 3 lSb are directly coupled together with an element 331 As illustrated, the element 331 attaches the moveable members 31 5a, 31 Sb together in a direction generally perpendicular to their direction of travel. Therefore, the element is preferably stiff or rigid to withstand bending The element 331 may be moved by an actuation means which comprises a means for 15 longitudinal displacement of the moveable members 31 5a, 31 Sb. 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 the instantaneous electric water heater The wax capsule will expand or contract depending on the temperature of the 20 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 path before or after the heater can 14, the water flow control device may be used in a thermostatic way, in particular varying the flow rate of water through the heater can 25 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 temperature. Of course, the water flow control device of Figure 5 may also be used with a 30 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 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 5 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.

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 10 illustrated embodiment, the moveable member 410 is tubular and the inside 41 1 of the member 410 defines part of the flow path for the water. First and second o-rings 41 5a, 41 5b are associated with each of the first and second moveable members 41 Oa, 41 Ob The outlet 420 of the fourth embodiment is positioned at the periphery and may be at least partly annular 15 The moveable members 410a, 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 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 20 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 water flow can be split and fed separately to each end of the moveable members However, with a hollow moveable member the amount of conduit 401 required for 25 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 embodiments of the present invention even where the first and second moveable members are not part of the same member. Indeed, the first and second moveable 30 members of the fourth embodiment may be made of one, two, three or more

-12 components 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 5 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 10 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 15 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 actuator 20 The water flow control device of the fifth embodiment comprises a first moveable member 510a (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 25 water inlet 502 perpendicular to the direction of movement of the first and second cores 51 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 S lea than on the second core S 1 Ob if those cores are exposed to the same water pressure in the inlet 502.

30 A valve 550 positioned between the water inlet 502 and the first moveable

-13 member 51 Oa (but not the second moveable member 510b) controls the difference in water pressure between the inlet 502 and the area adjacent the first moveable member 510a. The valve S50 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 5 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 S45) 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 51 Ob is blocked.

10 The second moveable member 510b 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 51 Ob.

15 The first moveable member 510a is also attached to an actuating rod 565.

Movement of the first moveable member 51 Oa 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 20 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 theon/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 25 second moveable member 510b moves away from the inlet 502 (i e. downstream and leftwards as illustrated) as a result of the biasing of spring 545. 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 51 Ob The path for water from the inlet 502 to the first moveable member 51 Oa is blocked by the valve 550 Therefore, the flow 30 control device of the fifth embodiment may be used to completely block off the flow

-14 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 of the first moveable member 510a is less than the pressure on the upstream side of 5 the second moveable member 51 Ob if the valve plate 540 is pushed away from valve o-ring 542. In this case, the upstream force of water on the second moveable member S lOb due to the water pressure in the inlet 502 and the force exerted on the second moveable member 510b by the spring 545 is such that the first and second moveable members 51 Oa, 510b will move to the left as illustrated (towards the inlet 10 i.e. upstream for the first moveable member 510a and away from the inlet i.e. downstream for the second moveable member S lob) until the valve plate 540 settles on the valve o-ring 542. In this position neither the first nor the second moveable members 51 Oa, 51 Ob experience pressure from water from the inlet 502. Thus7 there is no overall force on the moveable members 51 Oa, 51 Ob and as neither of the flow 15 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, 510b towards the right as illustrated.

20 This has the effect of increasing the flow rate through the flow control part of the first moveable member S lea 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 510b to the inlet 25 502

At this stage, the position of the first and second moveable members 510a, 51 Ob will be determined by an squalling 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 30 water pressure of the first moveable member 510a is larger than that of the second

-15 moveable member 51 Ob, a smaller pressure on the inlet side of the frst moveable member 51 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 5 the actuation of the switch 560 by the actuation rod 565.

In the open position resulting from valve 550 being at least partly opened, water flows both through the flow control path of the first and second moveable members 5 lea, 5 lob as defined by the longitudinal grooves 512a, 512b. The longitudinal grooves 512b have a cross sectional area which decreases before 10 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 offsuffcient water is in the heater can 14 to avoid boiling of 15 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 51 Oa, 51 Ob 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 20 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 25 moveable member 51Oa decreases whilst the pressure on the second moveable member 51Ob 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 5 lea, 5 lob Thus, the first and second moveable members 51Oa, 5 lob move to the left until the valve plate 540 shuts off the second moveable member 30 51 Ob from the inlet 502 by contacting with the valve seat 542.

-16 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 little flow passes 5 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 B is the same as that of the fifth embodiment illustrated in Figure 7 save as described below. In the sixth embodiment 10 the diameters of the first and second moveable members 61 Oa, 61 Ob 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, 610b. The second moveable member 610b does not have any longitudinal grooves such that the only flow control part of the device is defined as 15 the sum of cross sectional areas of the grooves 612a at the first o-ring 615a and the gap between the first moveable member 610b and the first o-ring 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 61 Oa.

20 As in the fifth embodiment, the position of the first and second moveable members 610a, 610b 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 I 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 25 varying the flow rate of water through the pilot valve 650 the position of the moveable members 610a, 610b can be varied and so thereby can the cross sectional area of the flow control part of the control device. As will be appreciated, the force required to move the pilot valve 650 will be quite high as the valve member will need to be moved against the full flow of water However, the mechanism of the pilot 30 valve can be chosen to take advantage of mechanical advantage (i e by providing a

-17 needle valve with a shallow pitched thread). However, the embodiment does allow control of a switch or switches by the cores possibly by using the extension member 640 as an actuator and has automatic shut down when either input water pressure fails or when the output is blocked. Also pressure regulation still occurs because of 5 the presence of the pressure regulating o-rings The second member 610b may also be provided with longitudinal grooves which have a larger cross-sectional area than the grooves 612a in the first member 6tOa. This arrangement allows majority flow to be controlled using minority flow so that, as in the fifth embodiment, the energy needed to operate the pilot valve 650 may 10 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 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 15 relating to automatic positional adjustment of the moveable members 510a, 510b, 61 Oa, 610b on pressure variation in the flow path. For example in the fifth 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 20 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 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, 51 Ob will 25 move to the left as illustrated thereby to stop power to the elements l S. The fifth embodiment can also provide automatic regulation of position of the first and second moveable members on variation of water pressure at the inlet 502 to keep the flow rate through the valve substantially constant. As pressure increases at inlet 502, a similar increase occurs upstream of the first moveabie member 51Oa and 30 so the flow rate will increase. As the flow rate increases the pressure drop across the

-18 pilot valve 550 and hence the differential pressure between first moveable member S l Oa and second moveable member 51 Ob will increase. This leads to moveable members 51 Oa, 51 Ob moving to the left as illustrated until a new stable position is reached where the effect of the pressure difference balances the spring force. This 5 leads in turn to a reduction in the cross sectional area available between the o-rings and cores hence stabilising the flow against the pressure increase. The opposite will happen for a decrease in pressure at the inlet 502 Figure 9 is a cross-section through the heater can 14 of Figure 2. The heater can incorporates two valves, one valve which is in accordance with the first 10 embodiment of the present invention and one valve which is in accordance with the fourth embodiment of the present invention.

The heater can is of the by-pass type in which the temperature of the water heated by the heater elements 18 is kept substantially constant. The user selects the desired output temperature of the water exiting the chimney at outlet 19 by selecting.= 15 a certain flow of water through a by-pass 17 which mixes with heated water in the chimney 16. The amount of water allowed through the by-pass 17 is selected using a valve according to the first embodiment of the present invention in which two.= moveable members l lea, 110b are moved in opposite directions relative to the flow of wafer pest them using a reck 130a, 130b end pinion 140arrangementwith the 20 moveable members moving along parallel but different directions. Water which is allowed through this valve is labelled B in the illustration.

The water which flows through the heating chamber of the heater can 14 and which flows past the heating elements 18 between the outer housing of the heater can 14 and the chimney 16 is regulated by a valve according to the fourth embodiment.

25 This is the embodiment where two moveable members 410a, 410b are joined and move along the same longitudinal axis with water passing through the centre of both of the members. In the embodiment illustrated in Figure 9 a wax capsule 450 is attached via a rod 420 to the moveable members 410a, 410b such that expansion or contraction of the wax capsule 450 affected by the temperature of the water 30 surrounding it affects the position of the moveable members 410a, 410b by

-19 expansion or contraction being transmitted by connecting rod 420 to regulate the temperature of the heated water by changing the flow rate past the heating elements 18. The heated water labelled H and the by-pass water labelled B are then mixed downstream of the wax capsule and exit through outlet 19.

5 Figure 10 illustrates in more detail the construction of the valve which regulates the flow of water past the heater elements 18 in Figure 9. As can be seen the moveable members 410a, 410b are formed in two parts each of which is injection moulded. A spacer 409 is formed on one of the moveable members 41 Oa, 41 Ob and the whole assembly is snap fitted together Of course the moveable members and 10 spacer may be integrally formed or may be formed of more than two or even three parts. The moveable members 410a, 410b may also be formed without a spacer element 409.

The connecting rod 420 passes into the housing of the valve through an orifice and is sealed by an o-ring 425 which is held in place by a retainer 426. The 15 second o-ring 415b which interacts with the second moveable member 410b is then positioned in the housing and held in place by a further retaining member 416, the first o-ring 415a is positioned on the other side of this further retaining member 416.

The rod 420 passes through all of the sealing o-ring 425, the retainer 426, the first and second o-rings 415a, 415b and the further retaining member 416 as well as the 20 first and second moveable members 410a, 410b and spacer member 409 The connecting rod is affixed to the moveable members through a fastening member 421.

A final sealing o-ring 429 seals the housing at the bottom of the valve as illustrated and a guiding member 430 is provided to guide the end of the rod 420 to ensure that the moveable members which are moved in the longitudinal direction by the rod 420 25 are maintained in alignment with the o-rings 415a, 415b The invention has been described with reference to o-rings around the orifices. Actually the invention works without these orings as the accuracy of the grooved area is not that important depending on the application. Further, lip seals (seals with an inward facing triangular cross-section) have been found to work well 30 as the thin part of the triangle does not squeeze into the grooves which is what can

-20 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 example the moveable members may be needle valves or the cores may have only one groove

Claims

-21 CLAIMS

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

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

3. A water flow control device according to claim 2, wherein at least one of said first and second moveable members is tubular and the inside of said at least one 20 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 second moveable members are part of the same member.

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6 A water flow control device according to clann 2, 3, 4 or 5, wherein said actuation means comprises a means for longitudinal displacement of said moveable members.

7 A water flow control device according to claim 6, wherein said means for 5 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 means comprises: a first rack attached to said first moveable member; 10 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 15 and a pinion for driving said rack, said first and second moveable members being movable along the same axis.

I 0. 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 20 connection member, said rack being driven by a pinion to move said first and second moveable members along different but parallel axes

11. 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 turning the 25 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 means is a valve in said flow path, actuation of which is effective, in use, to cause a 5 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.

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 10 the side of said inlet.

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

16 water flow control device according to claim 13, 14 or 15, wherein 15 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.

18. A water flow control device according to any one of claims 13 to 17, further 20 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 sew by coupling with said plate

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19 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.

20 A water flow control device according to claim 19, wherein the cross 5 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

21. A device according to claim 19 or 20, wherein at least one of said first and second moveable members is cylindrical with an outer surface cooperative with an 10 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 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.

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23. A device according to claim 22, wherein said circumferentially spaced 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 20 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 claims, wherein at least one of said first and second moveable members has a surface pattern and/or overall shape which changes along at least part of the longitudinal length of said member.

27. A device according to any one of the preceding claims, wherein at least one 5 of said first and second orifices are defined by annular orings

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

29. A method of controlling water flow rate in a flow path between an input and an output, said method comprising the steps of: 10 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 moving a first moveable member positioned in said first orifice and a second 15 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.

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

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

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