GB2390140A

GB2390140A - Instantaneous water heater

Info

Publication number: GB2390140A
Application number: GB0314018A
Authority: GB
Inventors: Dominic George Webber; Robin Craig Cocker; Peter Georg Laitenberger; Alan Michael Hart; Jocelin Langford
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
Also published as: GB0314018D0; GB0214541D0; GB2390137A

Abstract

The heater for a shower has a water inlet 8 or 10, a flow rate control valve 12, an on/off control valve 20, and a heater can 14. Water flows through the various components to an outlet 19 with the pressure drop minimised by having a cross-sectional area with no less than a 15mm internal diameter throughout the components. The flow path through the heater can has a cross-sectional area equivalent to a pipe of at least 15 mm internal diameter and, similarly, the on/off valve and flow rate control valve when fully open have cross-sectional areas equivalent to a pipe of at least 15 mm internal diameter to allow the required pressure and flow rate to be maintained. The pressure drop may also be minimised by eliminating any intermediate pipes between the components or by including a rolling diaphragm in the on/off valve.

Description

-1 INSTANTANEOUS WATER HEATER

The present invention relates to an instantaneous water heater and an on/off control valve for a shower allowing simplification of operation and design and 5 improved overall performance with regard to the different requirements for different seasons. A great variety of different types of instantaneous water heater are known.

These may be used in conjunction with a shower such that, when a user turns on a flow of water to the shower, the water is instantaneously heated to a desired 10 temperature. Often, the temperature control is achieved by varying the water flow rate through the heater can of the instantaneous water heater.

In order to allow the user to control the outlet temperature, a flow rate control valve is provided for varying the rate of flow of water through the heater can. With a low flow rate, the heater can will raise the temperature of the water more than with a 15 high flow rate.

A problem with this system is that the inlet water temperature can be significantly higher in summer than in winter. As a result, even with the variation achieved with the flow rate control valve for a given heater power, given the inlet pressures typically available for a domestic installation, the outlet temperature will 20 tend to be either too hot in summer or not hot enough in winter.

Known instantaneous water heaters overcome this problem by providing a heater can which can be switched between at least two different power ratings. For electric instantaneous water heaters, it is known to provide heating elements which can be switched by the user between ratings as low at 240Vac as 4.5kW and as high 25 as 10.8kW. Thus, in winter, to handle the lower inlet water temperatures, a higher power rating is selected by the user.

Although this arrangement works effectively, it is undesirably complicated to assemble, requiring multiple connections to the heater elements, together with associated wiring and switches. This adds significantly to the overall cost of the 30 instantaneous water heater.

This arrangement also makes the instantaneous water heater more difficult to use, since it is necessary to decide which power rating to select. This is particularly of concern at times between summer and winter when it is not clear whether a high power or a low power rating is required. The system is not particularly intuitive and 5 results in otherwise unnecessary service calls by users who do not understand how to operate it.

It is an object of the present invention to overcome or at least reduce these problems. According to the present invention, there is provided a method of 10 constructing an instantaneous water heater for a shower, the method including: providing a water inlet, a water outlet and components defining a flow path between the inlet and the outlet, said components including an on/offvalve, a flow rate control valve and a heater can; and constructing said components such that, when assembled and with the on/off 15 valve and flow rate control valve fully open, the pressure drop between the inlet and outlet is minimised.

According to the present invention, there is also provided an instantaneous water heater for a shower including: a water inlet; 20 a water outlet; and components defining a flow path between the inlet and the outlet, said components including an on/off valve, a flow rate control valve and a heater can; wherein said components are constructed such that, with the on/ofvalve and flow rate 25 control valve fully open, the pressure drop between the inlet and outlet is minimised.

By reducing the pressure drop in this way, it is possible to provide a very high flow rate through the heater can, such that, even in summer, it is possible to use a high power rating heating element. lIence, the instantaneous water heater may include a heater element of fixed power rating without any user operable switches to 30 change the power rating. It will be sufficient to use only the flow rate control valve to control the temperature both in winter and summer.

-3 Preferably, for a pressure drop across the instantaneous water heater of at least 1 bar, the outlet supplies water at at least 12 litres per minute.

With this flow rate, it is possible to achieve acceptable temperature control in both winter and surnner.

5 It will be appreciated that in practice the flow rate through the instantaneous water heater will depend on the inlet pressure and, hence, the pressure drop across it.

Hence, preferably, the instantaneous water heater is such that, for a pressure drop across it of between 0.75 bar and 2 bar, the outlet supplies water at at least 10 litres per minute.

10 This is a significant advance over prior art arrangements.

For pressures between l bar and 1.5 bar, the outlet is capable of supplying water not only at 10 litres per minute or 12 litres per minute, but preferably at at least 12.5 litres per minute.

Preferably, for higher pressure drops, even greater flow rates are possible.

15 For a pressure of at least 3 bar, the outlet supplies water preferably at at least 12 litres per minute, preferably at at least 14 litres per minute and more preferably at at least 15 1itres per minute. Indeed, for pressure drops of at least 6 bar, the outlet supplies water preferably at at least 15 litres per minute and more preferably at at least 16 litres per minute.

20 With these high flow rates, it is possible to fit the instantaneous water heater with a heater having a power rating suitable for winter use, but still achieve relatively little heating of the water in summer.

Preferably, with a heater can including a heater rated at respectively 8. 5 kW, 9.5kW or 1 0.5kW and a pressure drop over the instantaneous water heater of 1 bar or 25 more, the water in the instantaneous water heater is raised by less than 10 C, 11 C or 12 C respectively.

Hence, in Sumner, water need not be heated unduly.

Taking into account the fact that higher flow rates will be achieved for higher inlet pressures and' therefore, greater pressure drops, even lower temperature 30 increases may be achieved. For the same three heater ratings, the instantaneous water heater preferably raises temperature by less than 10 C, 11 C or 12 C respectively for o

- a pressure drop of 1 bar to 1.5 bar, 9 C, 10 C or 11 C respectively for a pressure drop of 2.5 bar to 3 bar and 8 C, 9 C or 10 C respectively for a pressure drop of 5.5 bar to 6 bar.

Hence, for higher inlet pressure and pressure drops, the instantaneous water 5 heater is capable of producing relatively small temperature rises such that it is suitable for surmiser use.

The {low rate control valve of the instantaneous water heater is intended to introduce a variable resistance to the flow through the instantaneous water heater.

Therefore, it is worthwhile considering the resistance to flow of water through the 10 instantaneous water heater for all parts other than the flow rate control valve.

In this respect, for flow rates of 15 litres per minute, 12 litres per minute, 10 litres per minute and 6 litres per minute, the pressure drop between the water inlet and the water outlet, excluding the flow rate control valve, is less than 0.2 bar, 0.14 bar, 0.1 bar and 0.04 bar respectively.

15 In this way, the desired flow rate and minimum temperature rises can be achieved. Preferably, the minimum cross-sectional area of the flow path as defined by the heater can and the on/off valve when fully open is equivalent to a pipe of at least 15mm internal diameter.

20 It is thus assured that the functional components do not provide undue flow restrictions such that the flow rates and pressure drops discussed above may be achieved. Indeed, with the on/off valve, the minimum crosssectional area of the flow path at all points between the inlet and outlet other than through the flow rate control 25 valve are preferably equivalent to a pipe of at least l5mrn internal diameter.

In order to reduce the pressure drop presented by the heater can, the heater can preferably has an elongate cross-section such that the flow path defined by the heater can has a relatively large cross-sectional area for the overall depth of the heater can. 30 Indeed, according to the present invention, there is provided a heater can for an instantaneous water heater, the heater can including an outer housing, a chimney

-5 axially disposed within the housing and a heater element located radially between the chimney and the housing such that a water flow path exists between the chimney and the housing around the heater element in cornnunication with a flow path axially within the chimney wherein the cross-sections of the housing, heating element and 5 chimney perpendicular to the axis are elongate in one direction within the cross-

section relative to a perpendicular direction within the cross-section.

In this way, the cross-sectional area of the flow path is increased, but the heater can is increased in overall size only in one direction. A heater can is thus provided with a greatly reduced pressure drop but of a size which still fits 10 conveniently behind a shallow front cover.

Preferably, the components are connected directly to one another without separate intermediate pipes so as minimise the length of flow from inlet to outlet.

By reducing the length of flow, the overall pressure drop is reduced.

Preferably the on/off control valve includes a valve diaphragm, a rolling 15 membrane around the periphery of the valve diaphragm, the rolling membrane supporting the valve diaphragm for movement substantially perpendicular to the plane of the valve diaphragm and guide walls defining a valve opening and a flow path from an inlet through the valve opening to an outlet.

According to the present invention, there is also provided an on/off control 20 valve for an instantaneous water heater, the on/off control valve having: a valve diaphragm; a rolling membrane around the periphery of the valve diaphragm, the rolling membrane supporting the valve diaphragm for movement substantially perpendicular to the plane of the valve diaphragm; and 25 guide walls defining a valve opening and a flow path from an inlet through the valve opening to an outlet; wherein the valve diaphragm is movable so as to open and close the valve opening with the rolling membrane allowing the valve diaphragm to open the valve opening to provide effectively substantially no disruption to flow.

By providing a valve diaphragm which has a rolling membrane allowing a 30 relatively significant amount of movement, in its open state the valve need not introduce any significant pressure drop.

-6 The valve diaphragm may be moveable so as to open and close the valve opening with the rolling membrane allowing the valve to provide effectively no disruption to flow. This may be achieved by moving the valve such that the cross section of the flow path from inlet to outlet is completely clear. The valve is 5 preferably able to expose 70% to 100% ofthe flow path, but at least 50% ofthe inlet cross-section may be sufficient.

A valve member may be attached to the valve diaphragm so as to extend into the flow path to close the valve opening, with the rolling membrane allowing the valve diaphragm and the attached valve member to move away from the valve 10 opening so as to open the valve opening with the valve member substantially withdrawn from the flow path.

By providing the valve member on the valve diaphragm, the surface for sealing the valve opening can be retracted away from the valve opening to a position such that, when open, the valve does not introduce a significant pressure drop.

15 Indeed, with the valve member extending from the valve diaphragm across the flow path, as soon as the seal with the valve opening is broken, a significant amount of flow is allowed, the valve member itself providing relatively little resistance. This is in contrast to prior art diaphragm arrangements in which the daphragn itself is close

to the flow of water through the valve opening and interferes with the flow.

20 Where a valve diaphragm is used to close a valve opening, it is known to provide a protruding ridge which forms the valve opening and on to which the valve diaphragm or an extension thereof seals. This has the disadvantage that water flows up and over the surrounding ridge and then down through the valve opening, the convoluted flow path introducing an unwanted pressure drop.

25 Preferably, the guide walls defining the water flow path from the inlet to the valve opening form a duct with substantially parallel walls and the valve opening is formed as an opening in the substantially parallel walls on one side of the duct.

In this way, there are no walls or substantial ridges surrounding the valve opening and restricting flow.

30 Preferably the valve diaphragm is located on substantially an opposite side of said duct from the valve opening.

-7 In this way, the valve diaphragm can conveniently operate to open and close the valve opening and, in the open position, can be positioned so as not to interfere with flow through the valve opening.

Preferably, with the valve member closing the valve opening, the valve S member extends substantially across said duct from said opposite side.

In this way, the valve diaphragm itself can be kept substantially out of the flow path.

In its fully extended position, the valve diaphragm should preferably not extend beyond the surrounding walls of the control chamber. The walls should not 10 extend into the flow path to ensure that they do not interfere with flow along that path. Therefore, the valve diaphragm likewise should not extend into the flow path.

By providing the valve member extending across the duct, it is possible to position the valve diaphragm no more than flush with the walls defining the duct.

Preferably, the valve member has an end face sealing the valve opening and 15 the rolling membrane allows the valve diaphragm and the attached valve member to move away Dom the valve opening such that the end face is substantially flush with the substantially parallel walls of said duct on said opposite side.

In this way, with the valve opening fully open, the valve member does not extend into the flow path and, hence, does not interfere with flow to the valve 20 opening.

Preferably, the on/off control valve further includes a valve control chamber formed by valve chamber walls and a valve diaphragm, the rolling valve membrane sealing the valve diaphragm to the valve chamber walls and a chamber bleed orifice bung formed in the valve chamber walls such that a pilot valve can control pressure 25 in the valve control chamber so as to move the valve diaphragm towards and away from the valve opening.

This provides a simple and effective way of operating the valve.

Preferably a resilient member is provided within the valve control chamber for biassing the valve diaphragm towards the valve opening thereby shutting off the 30 flow of water.

-8 In this way, the valve is opened by reducing the pressure within the valve control chamber relative to the pressure on the outer face of the valve diaphragm.

With equalisation of pressure, the valve will automatically close by means of the resilient member.

5 Preferably the on/off control valve further includes a power switch actuator for providing movement to switch on and off heating in the instantaneous water heater, the power switch actuator having a switch diaphragm, a switch control chamber formed by switch chamber walls and an inner face of the switch diaphragm, the outer face being in fluid communication with water upstream of the valve 10 opening, and a pilot orifice formed in the switch chamber wall such that a pilot valve can control the pressure in the switch control chamber so as to move the switch diaphragm. In this way, heating of water within the instantaneous chamber is controlled by means of relative water pressures within and outside the switch control chamber.

15 Preferably a resilient member is provided within the switch control chamber for biassing the switch diaphragm so as to engage the switch control member.

In this way, reducing the relative pressure within the switch control chamber can be used to turn on the heater, such that, with equalization of the pressure, the power switch actuator will automatically turn off the heater by virtue of the resilient 20 member.

Preferably, the chamber bleed orifice joins the valve control chamber to the switch control chamber such that the pilot orifice enables a pilot valve to control pressure in both the valve control chamber and the switch control chamber.

In this way, a single pilot valve may be used to control the pressures in the 25 valve control chamber and switch control chamber relative to the pressure upstream of the valve opening. Hence, the heater will be turned on when the valve opening is opened and turned off when the valve opening is closed.

Preferably, a switch bleed orifice is provided through the switch diaphragm such that the switch diaphragm does not move from an off position until after the 30 valve diaphragm opens the valve opening, but moves back to the off position before the valve diaphragm closes the valve opening.

-9- In particular, when the pilot orifice is opened to a lower pressure, the valve diaphragm will move immediately so as to open the valve opening and the switch diaphragm will subsequently move to turn on the heater. In contrast, when the pilot orifice is closed, water will feed through the switch bleed orifice so as to move the 5 switch diaphragm and turn off the heater before sufficient water bleeds through the chamber bleed orifice to move the valve diaphragm to the valve opening closed position. Preferably, the on/off control valve further includes a pilot valve for providing selective fluid communication to an extension of the flow path 10 downstream ofthe on/off control valve.

In particular, the on/off control valve can be fitted in an instantaneous water heater with the pilot valve so connected.

Preferably, the pilot valve may provide selective cormnunication to water in the heater can of the instantaneous water heater.

15 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 according to the present invention; 20 Figure 2 illustrates an exploded view of the functional components of an instantaneous water heater according to the present invention; Figures 3 illustrates the assembled components of Figure 2; and Figures 4 (a) and (b) illustrate, for heaters of different power ratings, the temperature rise of water flowing through the heaters according to flow rate; 25 Figures 5 (a) and (b) illustrate a table and graph for a range of instantaneous heaters showing maximum flow rate for different pressure drops; Figure 6 (a) illustrates, for a range of instantaneous heaters and a nominal power rating of 8.5kW, the minimum temperature rise for various pressure drops; Figure 6 (b) illustrates, for a range of instantaneous heaters and a nominal 30 power rating of 9.51cW, the minimum temperature rise for various pressure drops;

-10 Figure 6 (c) illustrates, for a range of instantaneous heaters and a nominal power rating of 10.5kW, the minimum temperature rise for various pressure drops; Figure 7 (a) illustrates for the preferred embodiment the relationship between flow rate and pressure drop excluding any effect of the flow rate control valve; S Figure 7 (b) illustrates the relationship between flow rate and pressure drop for five settings of the flow rate control valve; Figure 8 illustrates a cross section through a preferred heater can; Figure 9 illustrates in more detail the valve components of Figure 2; and Figure 10 illustrates schematically the operation of a preferred on/off control 10 valve.

As illustrated in Figure 1, an instantaneous water heater includes a front cover 2 including a water temperature control 4 and an on/off button 6.

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

15 Figure 2 illustrates a suitable arrangement of components embodying the present invention. However, it should be appreciated that many other arrangements could be provided within the scope of the invention as defined by the claims.

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 valve 12 to the 20 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.

An on/offcontrol valve 20 operates under the control of a button 22 to control whether or not there is any flow from the inlets 8 or I O to the flow rate control valve 25 l 2. Dependant on the flow of water through the water heater, an ann 24 operates an electrical switch 26 to turn on or off power to the heater element 18.

The flow rate control valve 12 may be operated by a rotatable member 28 so as to vary the flow rate through the heater can 14 and, hence, the outlet temperature.

It should be noted that there is only a switch for fuming power to the heater 30 element 18 on or off. There is no switch for selecting between two or more elements so as to select a desired power rating.

-11 Figure 3 illustrates the assembled components without the cover 2.

It will be appreciated that, in order to provide an acceptable shower, the water flow rate should be no less than in the region of 2.5 Iitres per minute. For this flow rate, the heater can of the instantaneous water heater must be of sufficient power to 5 heat the water to temperatures required by the user. This is clearly of most concern during the winter season when the inlet water temperature is at its coldest.

For electrically heated instantaneous water heaters, power of ratings of 8.5kW, 9.5kW and 10.5kW will be considered. A preferred embodiment uses a 10.5 kW heater. It is possible to use heaters of higher power ratings, but then there 10 are other considerations in providing appropriate electrical wiring for heater elements having power ratings above 10.8 kW.

The table of Figure 4 (a) and the corresponding graph of Figure 4 (b) illustrates the temperature rise of water flowing through heaters of different power ratings according to the flow rate.

15 Thus, as illustrated even for a flow rate of 3 litres per minute, even a 8.5 kW heater is able to raise the water temperature, such that, in winter, an acceptable outlet temperature rise of 40 C can be achieved, providing a shower of perhaps 45 C.

As explained above, by operating the flow rate control valve 12, the flow rate through the heater can 14 can be increased such that the water is heated by a lesser 20 amount and the outlet water is provided at a lower temperature.

With the flow rate control valve fully open, the maximum achievable flow rate through an instantaneous water heater will depend on the achievable inlet pressure and, hence, the pressure drop. The table of Figure 5 (a) and the corresponding graph of Figure 5 (b) illustrate measured maximum flow rates for a 25 range of known instantaneous heaters with different pressure drops. The tables of Figures 6 (a) to (c) illustrate the corresponding minimum temperature rises for nominal power ratings of 8.5 kW, 9.5 kW and 10.5 kW respectively.

Thus, it can be seen that with previous instantaneous water heaters, even a heater of only 8.5 kW will heat the water significantly. With higher summer inlet 30 water temperatures, this will result in a minimum outlet temperature from the

-12 instantaneous water heater which is above the lower range which users require and hence is unacceptable.

This problem may be overcome by providing a heater which can be switched between two different power ratings. By providing a high power rating for winter 5 use and a low power rating for summer use, a flow rate control valve is able to provide acceptable outlet temperatures both in summer and winter.

The present invention is based on a recognition that the maximum flow rates indicated in Figures 5 (a) and (b) result from the design and construction of all of the components between the inlet and outlet of the instantaneous water heater and that, to by designing and constructing the components to reduce the pressure drop between the inlet and outlet, a higher flow rate can be provided when the flow rate control valve is fully open. Indeed, the present invention is also based on a recognition that, if a higher flow rate can be provided, the higher power rating used for winter can also be used during the summer. This avoids the need for additional wiring and switching l 5 to switch power ratings. It also simplifies operation for the user who is now provided with a single temperature control knob and no power rating switch(es).

Thus, the heater element l 8 is provided as a single power rating and the instantaneous water heater is not provided with any user operable switch to allow the output power to be selectively changed.

20 The heater element may have a power of 8.5 kW. However, preferably, higher power ratings are provided, such as 9.5 kW or 10.5 kW. As mentioned above, higher power ratings are also possible, but, above 10.8 kW, other considerations are required with regard to the electrical connections and wires.

In practice, the heater element l 8 may be comprised of 2 sub-elements which 25 are connected together. By making available sub-elements of two different power ratings, it is possible to provide a range of instantaneous water heaters of different power ratings by combining together the sub-elements appropriately. For instance, by providing subelements having ratings of 4.25 kW and 5.25 kW, overall heater elements l 8 may be provided with ratings of 8.5 kW, 9.5 kW or 10.5 kW.

30 As discussed above, this arrangement can be more difficult to use, since it is necessary to decide which power rating to select.

To

-13 Figures 5(a) and (b) illustrate the flow rate achievable with a preferred embodiment of the present invention.

As will be discussed further below, components within the instantaneous water heater are constructed so as to minimise their resistance to water flow and, 5 hence, provide a high flow rate.

Inevitably, as Figure 5(b) illustrates, for any design, the available flow rate will tend to flatten off as the inlet pressure (and hence pressure drop across the instantaneous water heater) increases. However, with the components of the instantaneous water heater designed so as to minimise flow resistance, water flow 10 rates climb rapidly for low pressure drops and flatten out or plateau at flow rates much higher than the prior art arrangements.

As a result and as illustrated in Figures 6(a) to (c), for 8.5kW, 9.5kW or 10.5kW heaters, the preferred embodiment can achieve temperature rises much smaller than those in the prior art. In particular, even for only a I bar pressure drop

15 with a 10.5kW heater (see Figure 6(c)), a temperature rise of only 11. 9 C is possible.

In this way, it becomes possible to use a heater with only one single predetermined power rating. In the winter, with the flow rate control valve restricting flow to, for instance, 3 litres per minute, the heater is able to raise the water temperature significantly so as to provide the desired outlet water temperature. On 20 the other hand, in the summer, with the flow rate control valve fully open so as to provide maximum flow, a sufficiently high flow rate (for instance 12.5 to 16 litres per minute as illustrated in Figure 5(a)) ensures only a small rise in water temparture such that the outlet water temperature is not too hot. The user interface of the instantaneous water heater may thus be

simplified 25 without the need for any switching between different power ratings.

It will be appreciated that the flow rate control valve is intended to introduce a variable restriction and pressure drop so as to vary the flow rate through the heater can. Figure 7(a) illustrates for the preferred embodiment the relationship between 30 flow rate and pressure drop for the flow path through the instantaneous heater excluding any effect of the flow rate control valve.

-14 By way of comparison, Figure 7(b) illustrates the relationship for five settings, settings l to 5 of. the flow rate control valve.

In order to achieve the desired flow rates, the instantaneous water heater has a reduced pressure drop between the inlet and outlet. In particular, the components are 5 designed, constructed and assembled such that the pressure drop from inlet to outlet is minimized. The components may be arranged so as to provide a total pressure drop far less than was previously known.

As will be appreciated from Figure 2, the flow path the inlet and outlet (as defined by all of the various components of the instantaneous water heater) has, at to each point along its length, a cross-sectional area defined by the component at that position. As the cross-sectional area is reduced, the pressure drop increases and water flow is resisted. It has been found that, by providing, for the flow path other than through the flow rate control valve, a cross-sectional area no less than the equivalent of a lSmm internal diameter pipe, the required pressure drops and flow l 5 rates may be achieved.

Apart from the interconnecting conduit walls, the key water flow functional components of the instantaneous water heater are the on/off valve, the flow rate control valve and the heater can. The flow rate conko1 valve, according to its intended function, restricts flow. However, the flow path through the heater can 20 should have a cross-sectional area which is equivalent to a pipe of at least l Srnm internal diameter and similarly, the ordoff valve 20 should, when fully open, have crosssectional areas equivalent to a pipe of at least l 5mm internal diameter.

By providing such components with interconnecting conduits also having minimum cross-sectional areas equivalent to a pipe of at least 1 5mm internal 25 diameter, the total pressure drop between inlet and outlet may be minimised so as to achieve the required flow rates discussed above.

The length of the flow path from mlet to outlet also influences the total pressure drop. In particular, the pressure drop is larger for longer flow paths.

Thus, for the preferred embodiment, the various components are connected 30 directly to one another without the use of separate intermediate connecting pipes.

-15 As illustrated in Figure 2, the on/off valve 20 and the flow rate control valve 12 are formed within a valve body comprising a first body part 30 attached to a second body part 32.

The first body part 30 joins with the second body part 32 so as to form the 5 required cavities for the on/off valve 20 and [low rate control valve 12 and has walls defining conduits between the valves. The inlets 8 and 10 are formed integrally in the second body part 32 and walls in the second body part 32 define the flow path to the ordoff valve 20.

The first body part 30 forms a lower wall for the heater can 14 and walls in 10 the first body part 30 form the flow path from the flow rate control valve into the heater can 14. Similarly, where the first body part 30 forms the lower wall of the heater can 14, it also includes walls defining a flow path from the heater can 14 to the outlet 19.

Thus, no intermediate connecting pipes are provided between the various 15 functional components and the components themselves include walls defining conduits connecting them to adjacent functional components in the flow path. In this way, the functional components are provided close to one another along the flow path and the overall length of the flow path is reduced. Furthermore, the number of joints between components in the flow path is also reduced. Since joints often introduce 20 discontinuities in the flow path walls and, hence, introduce pressure drops, a reduction in the number of the joints in the flow path also reduces the overall pressure drop.

It should be noted that, whenever a fluid flow has a change in direction, the fluid flow is accelerated and requires energy. Hence, any changes in direction 25 introduce pressure drops.

Therefore, in order to provide the fluid rates discussed above, it is proposed to provide a method of construction whereby the various components are fitted together so as to minimise the number of changes and amount of change of direction of the water flow in the flow path.

30 In order to minimise the pressure drop across the heater can 14, it is necessary to increase the internal cross-sectional area of the chimney feeding the outlet and also

-16- the area of the space outside the chimney in which the heating element is located.

Previously, heater cans have been substantially cylindrical. This is advantageous, since heater elements of this form are widely available and may be formed easily by constructing the element in the shape of a helix. Furthermore, for a given internal 5 cross-sectional area, the materials required for the heater can are minimised.

Following the proposals of the present application to increase the cross-

sectional area of the flow path, it is considered that the diameter of the heater can could merely be increased.

Instead of this, the present application proposes that the cross-section of the 10 heater can should be elongated in a direction perpendicular to the axis. In other words, the cross-sectional area of the heater can 14 is lozenge or oblong in shape as illustrated in Figure 8. In this way, the cross-sectional area of the flow path through the heater can is increased, but the heater can will still fit behind a relatively shallow cover 2. By positioning the heater can 14 behind the cover 2 of the instantaneous 15 water heater with its longer dimension (of the lozenge shaped cross-section) parallel to the front face of the cover 2 and, hence, the wall to which it is to be mounted, it is possible to increase the cross-sectional area of the flow path through the heater can 14 without making the instantaneous water heater or the cover 2 any deeper.

It will be appreciated that the flow rate control valve is designed specifically 20 to provide a variable cross-sectional area so as to vary flow rate for the purpose of controlling temperature. Although not essential to the present invention, it would be possible to adapt a flow rate control valve such that, in its fully open state, it provides no greater resistance to flow than is required for the flow rates discussed above.

As mentioned above, in order to provide the desired flow rates, the on/off 25 control valve, when open, should provide a cross-sectional area equivalent to a pipe of at least lSnun internal diameter.

Where a valve is provided which is directly operable by the user, such that the user operates the valve manually throughout its travel from a fully closed to a fully open position, such a cross-sectional area can be provided without difficulty.

30 However, it is preferred to provide an on/off valve which is functionally bi-stable such that it is only necessary for a user to initiate a change between the on and off

-17- states for the valve to move, without energy from the user, between these states. It is also preferable that the valve only remains in its onlopen position as long as normal inlet water pressure is maintained. Indeed, an on/off switch for controlling power to the heater element of the instantaneous water heater can be linked to the on/off valve 5 and it would be undesirable to allow the heater element to remain turned on in a situation where the water supply has been interrupted.

In order to meet these requirements, it is known to construct the on/off valve with a diaphragm controllable by means of a pilot valve.

Starting from a closed state, the pilot valve opens a chamber on a back l O surface of the diaphragm to a downstream portion of the flow path having a reduced pressure. The diaphragm therefore moves in the direction of the back surface so as to open the valve and allow flow. When the pilot valve closes the chamber behind the back surface of the diaphragm or when the inlet water pressure drops, there is no differential pressure across the diaphragm and it moves back, for instance by virtue 15 of a return spring, to close the valve. Although this previous arrangement provides the required functionality in opening and closing the on/offcontrol valve, the diaphragm is only able to move by a small amount, such that, in its open state, it provides a substantial pressure drop and restriction to flow rate. Indeed, furthermore, diaphragm valves usually seal against a protruding peripheral wall requiring a 20 substantial change in flow direction and undesirable pressure drop.

Figure 9 illustrates in more detail the valve components of Figure 2 and Figure to illustrates schematically the operation of those components.

The onloff control valve 20 includes a valve diaphragm 40 which is sealed to the walls of a control chamber 42 by means of a peripheral rolling membrane 44. A 25 valve member 46 extends from a front face of the valve diaphragm 40. By means of the rolling membrane 44, the valve diaphragm 40 is able to move laterally, perpendicular to the plane of the diaphragm, in and out of the chamber 42. In this respect, the rolling membrane 44 has a relatively large extent so as to allow a significant movement of the valve diaphragm 40. In a preferred embodiment, the 30 valve diaphragm 40 is able to move by at least lOmm and preferably by at least 1 4mm, for instance l 4.5mm.

o

-18 The walls of the on/off control valve define a flow path 48 extending from an inlet 50 of the on/off control valve to a valve opening 52. The inlet 50 is in fluid communication with the main inlet 8,10 of the instantaneous water heater.

As illustrated, the valve diaphragm 40 and control chamber 42 are positioned 5 opposite the valve opening 52 across the fluid path 48. The valve member 46 may thus extend across the flow path 48 so as to close the valve opening 52.

In the preferred and illustrated embodiment, the valve opening 52 is provided merely as an opening in the walls of the flow path 48 without any substantial walls or protrusions around the valve opening 52.

l O Thus, when the valve diaphragm moves inwardly of the chamber 42, the valve member 46 is moved away from the valve opening 52 so as to open the valve opening 52 and allow a flow of water from the inlet 50 to the flow rate control valve l 2 downstream of the on/off control valve. In the preferred embodiment, the rolling membrane 44 allows the valve diaphragm 40 to move inwardly of the control l 5 chamber 42 to such an extent that the valve member 46 is withdrawn from the flow path 48.

Preferably, in the fully withdrawn position 70% to 100% of the flow path 48 is exposed or free. However, 50% might suffice in particular arrangments.

The flow path 48 can be considered to be a duct having substantially parallel 20 side walls. In the offer closed position illustrated in Figure lO, the valve diaphragm can be positioned flush with those side walls so as, in effect, to form part of the side walls themselves. In this way, from the moment that the valve diaphragm 40 and valve member 46 move to open the valve opening 52, the valve diaphragm 40 is moved out of the flow of any water through the flow path 48. Preferably, with the 25 on/offcontrol valve m its on or open position, the valve diaphragm 40 is withdrawn into the chamber 42 to such an extent that an end face of the valve member 46 then lies substantially flush with the walls of the duct or flow path 48. In this way, the valve diaphragm 40 and valve member 46 provide substantially no impedance to flow of water within the flow path 48 and through the valve opening 52. However, 30 with the valve member 46 still partly protruding from the walls, the flow path may still remain free or exposed to the ranges mentioned above.

-19 As illustrated, a chamber bleed orifce 54 is provided in the walls of the chamber 42. This allows water to bleed in and out of the control chamber 42 so as to allow the valve diaphragm 40 to move. In particular, the chamber bleed orifice is in fluid communication with a pilot orifice 56 and an associated pilot valve 58.

5 The pilot valve 58 selectively connects the pilot orifice 56, bleed orifice 54 and chamber 42 to water downstream of the onJoff control valve, in particular at a position where there is at least a slight pressure drop with respect to the water pressure in the on/off control valve.

In the off or closed position illustrated in Figure l O. a resilient member 60, lO such as a coil spring, biases the valve diaphragm 40 outwardly of the chamber 42 so as to close the valve opening 52. However, if the pilot valve 58 is opened, for instance by means of pilot valve stem 62, the pressure on the inside of control chamber 42 and hence the pressure on the inner face of valve diaphragm 40 is reduced to that of the downstream water pressure to which the pilot valve connects.

l 5 The higher pressure on the outer face of the valve diaphragm 40 therefore moves the valve diaphragm 40 inwardly of the control chamber 42 against the resistance of the resilient member 60. As discussed above, the components are arranged such that the valve diaphragm 40 will move until the valve member 46 is completely clear of the valve opening 42.

20 As illustrated, a fluid connection 64 also connects, via a switch actuator 66 to be described below, the chamber bleed orifice 54 to water upstream of the valve opening 52. In this way, when the pilot valve 58 is again closed, the fluid connection 64 causes the pressure in the control chamber 42 and on the inner face of the valve diaphragm 40 to equalise with the water pressure in the flow path 48 and on the outer 25 face of the valve diaphragm 40. By virtue of the resilient member 60, the valve diaphragm 40 then moves outwardly of the control chamber 42 so as to close the valve opening 52.

As mentioned above, the ordoff control valve also includes a power switch actuator 66. This is responsive to water pressure and movement of the valve 30 diaphragm 40 so as to turn on or off any heating in the instantaneous water heater, such as heat element 18.

-20 The power switch actuator includes a switch diaphragm 68 which is sealed to the walls of a switch control chamber 70 by means of a membrane 72. This membrane 72 may be of conventional constructions and need not allow signficant movement of the diaphragm 68.

5 In the preferred embodiment, at least one wall of the switch control chamber 70 is in common with the walls of the valve control chamber 42. As illustrated, the chamber bleed orifice connects the switch control chamber 70 and valve control chamber 42. The pilot orifice 56 is then provided in the walls of the switch control chamber 70.

10 A resilient member 74, such as a coil spring, biases the switch diaphragm 68 outwardly of the switch control chamber 70 and a switch bleed orifice 76 is provided in the switch diaphragm 68 so as to connect the switch control chamber 70 to the fluid connection 64.

In use, when the pilot valve 58 is opened, the pressure in both the valve 1 S control chamber 42 and switch control chamber 70 is reduced such that, not only does the valve diaphragm 40 move to open the valve opening 52, but the switch diaphragm 68 moves inwardly against the resistance of the resilient member 74 so as to turn on a heater in the instantaneous water heater. In the preferred embodiment, however, the relative dimensions of the bleed orifices are chosen such that the valve 20 diaphragm 40 will move before the switch diaphragm 68. In this way, it is ensured that there is a flow of water through the instantaneous water heater before heating is started. When the pilot valve 58 is closed, by virtue of the fluid connection 64, switch bleed orifice 76 and chamber bleed orifice 54, the water pressure in the switch 25 control chamber 70 and valve control chamber 42 will rise to that of the water upstream of the valve opening 52. In the preferred embodiment, due to the relatively small amount of movement of the switch diaphragm 68, the diaphragm 68 will move under the force of the resilient member 74 so as to turn off any heater before the valve diaphragm 40 completes its travel to close the valve opening 52.

30 In this way, it is ensured that the flow of water through the instantaneous water heater is not shut off until after any heating has ceased.

-21 In the preferred embodiment, as illustrated, the pilot valve 58 provides a connection to an extension of the flow path downstream of the flow rate control valve 12. This ensures that there is a pressure drop between the outer face of the valve diaphragm 40 and the pilot valve connection.

5 Finally, it will be seen from Figure 9 that the rolling membrane 44 can be constructed as part of the seal for sealing the first body part 30 to the second body part 32.

Claims

-22 CLAIMS

1. An instantaneous heater for a shower including: a water inlet; 5 a water outlet; and components defining a flow path between the inlet and the outlet, said components including an on/off valve, a flow rate control valve and a heater can; wherein said components are constructed such that, with the on/off valve and flow rate 10 control valve fully open, the pressure drop between the inlet and outlet is minimised.

2. An instantaneous water heater according to claim 1 wherein, for a pressure drop across the instantaneous water heater of at least one bar, the outlet supplies water at at least 12 litres per minute.

15 3. An instantaneous water heater according to claim 1 wherein, for a pressure drop across the instantaneous water heater of between 0.75 bar and 2 bar, the outlet supplies water at at least 10 litres per minute.

4. An instantaneous water heater according to claim I or 3 wherein, for a 20 pressure drop across the instantaneous water heater of between 1 bar and 1.5 bar, the outlet supplies water at at least 101itres per minute, preferably at at least 12 litres per minute and more preferably at at least 12.5 litres per minute.

5. An instantaneous water heater according to claim 1, 3 or 4 wherein, 25 for a pressure drop across the instantaneous water heater of at least 3 bar, the outlet supplies water at at least 12 litres per minute, preferably at at least 14 1itres per minute and more preferably at at least 15 litres per minute.

6. An instantaneous water heater according to any one of claims 1 and 3 30 to 5 wherein, for a pressure drop across the instantaneous water heater of at least 6

-23 bar, the outlet supplies water at at least 12 litres per minute, preferably at at least 15 litres per minute and more preferably at at least 16 litres per minute.

7. An instantaneous water heater according to any preceding claim 5 wherein, with a heater can including a heater rated at respectively 8.5kW, 9.5kW or 10.5kW and a pressure drop over the instantaneous water heater of 1 bar or more, the water in the instantaneous water heater is raised by less than 10 C, 11 C or 12 C respectively. 10 8. An instantaneous water heater according to any one of claims 1 to 6 wherein, with a heater can including a heater rated at respectively 8.5kW, 9.5kW or 1 O.5kW and a pressure drop over the instantaneous water heater of I bar to 1.5 bar, the water in the instantaneous water heater is raised by less than 10 C, 11 C or 12 C respectively. 9. An instantaneous water heater according to any one of claims 1 to 6 and 8 wherein, with a heater can including a heater rated at respectively 8.5kW, 9.5kW or lO.5kW and a pressure drop over the instantaneous water heater of 2.5 bar to 3 bar, the water in the instantaneous water heater is raised by less than 9 C, 10 C 20 or 11 C respectively.

10. An instantaneous water heater according to any one of claims 1 to 6, 8 and 9 wherein, with a heater can including a heater rated as respectively 8.5kW, 9.5kW or 1 0.5kW with a pressure drop over the instantaneous water heater of 5.5bar 25 to 6 bar, the water in the instantaneous water heater is raised by less than 8 C, 9 C or 10 C respectively.

11. An instantaneous water heater according to any preceding claim wherein, for at least one of the flow rates of 15 litres per minute, 12 litres per minute, 30 10 litres per minute and 6 litres per minute, the pressure drop between the water inlet

-24 and the water outlet, excluding the flow rate control valve, is less than 0.2 bar, 0.14 bar, 0.1 bar and 0.04 bar respectively.

12. An instantaneous water heater according to any preceding claim wherein the minimum cross-sectional area of the flow path as defined by the heater 5 can and the on/off valve when fully open is equivalent to a pipe of at least 15mrn internal diameter.

13. An instantaneous water heater according to claim 12 wherein, with the on/offvalve fully opens the minimum cross-sectional area ofthe flow path at all points between the inlet and outlet other than through the flow rate control valve is 10 equivalent to a pipe of at least l5mrn internal diameter.

14. An instantaneous water heater according to any preceding claim wherein the heater can has an elongate cross-section such that the flow path defined by the heater can has a relatively large cross-sectional area for the overall depth of the heater can.

l S 15. An instantaneous water heater according to any preceding claim wherein said components are connected directly to one another without separate intermediate pipes so as to minimise the length of flow from inlet to outlet.

16. An instantaneous water heater according to any preceding claim wherein 20 the heater can includes only one heater, said one heater having a predetermined power rating; and the instantaneous water heater does not include any switching for varying the power of said one heater.

17. An on/off control valve for an instantaneous water heater, the on/off 25 control valve including: a valve diaphragm; a rolling membrane around the periphery of the valve diaphragm, the rolling membrane supporting the valve diaphragm for movement substantially perpendicular to the plane of the valve diaphragm; and 30 guide walls defining a valve opening and a flow path from an inlet through the valve opening to an outlet; wherein p

-25 the valve diaphragm is movable so as to open and close the valve opening with the rolling membrane allowing the valve diaphragm to open the valve opening to provide effectively substantially no disruptions to flow.

18. An on/offcontrol valve according to claim 17 wherein, in the open 5 position, the valve diaphragm is positioned to expose a cross-sectional area for the flow path between 70% and 100% of the cross-sectional area of the inlet.

l9. An on/offcontrol valve according to claim 17 or 18 wherein the rolling membrane allows at least I Omm of movement between open and closed positions. 10 20. An on/off control valve according to claim 17, 18 or 19 wherein a valve member is attached to the valve diaphragm so as to extend into the flow path to close the valve opening and the rolling membrane allows the valve diaphragm and the attached valve member to move away from the valve opening so as to open the valve opening with the valve member substantially withdrawn from the flow path.

15 21. An on/off control valve according to claim 20 wherein the guide walls defining the water flow path from the inlet to the valve opening form a duct with substantially parallel walls and the valve opening is formed as an opening in the substantially parallel walls on one side of the duct.

22. An on/off control valve according to claim 21 wherein the valve 20 diaphragm is located on substantially an opposite side of said duct from the valve opening. 23. An on/off control valve according to claim 22 Wherein, with the valve member closing the valve opening, the valve member extends substantially across said duct from said opposite side.

25 24. An on/off control valve according to claim 22 or 23 wherein the valve member has an end face sealing the valve opening and the rolling membrane allows the valve diaphragm and the attached valve member to move away from the valve opening such that the end face is substantially flush with the substantially parallel walls of said duct on said opposite side.

30 25. An on/off control valve according to any preceding claim further including a valve control chamber formed by valve chamber walls and the valve

-26 diaphragm, the rolling membrane sealing the valve diaphragm to the valve chamber walls and a chamber bleed orifice being formed in the valve chamber walls such that a pilot valve can control pressure in the valve control chamber so as to move the valve diaphragm towards and away from the valve opening.

5 26. An on/off control valve according to claim 25 further including a resilient member within the valve control chamber for biassing the valve diaphragm towards the valve opening.

27. An on/off control valve according to claim 25 or 26 further including a power switch actuator for providing movement to switch on and off heating in the 10 instantaneous water heater, the power switch actuator having: a switch diaphragm; a switch control chamber formed by switch chamber walls and an inner face of the switch diaphragm, the outer face being in fluid communication with water upstream of the valve opening; and 15 a pilot orifice formed in the switch chamber walls such that a pilot valve can control pressure in the switch control chamber so as to move the switch diaphragm.

28. An on/off control valve according to claim 27 further including a resilient member within the switch control chamber for biassing the switch diaphragm so as to enlarge the switch control chamber.

20 29. An on/off control valve according to claim 27 or 28 wherein the chamber bleed orifice joins the valve control chamber to the switch control chamber such that the pilot orifice enables a pilot valve to control pressure in the valve control chamber and the switch control chamber.

30. An on/off control valve according to claim 29 further including a 25 switch bleed orifice though the switch diaphragm such that the switch diaphragm does not move from an off position until after the valve diaphragm opens the valve opening, but moves back to the off position before the valve diaphragm closes the valve opening.

31. An on/off control valve according to any preceding claim further 30 including a pilot valve for providing selective fluid communication to an extension of the flow path downstream of the on/off control valve.

-27 32. An instantaneous water heater including an on/off control valve according to any one of claims 17 to 30.

33. An instantaneous water heater including: an on/off control valve according to claim 31; 5 a flow control valve; and a heater can; wherein the pilot valve provides selective communication to water in the heater can.

34. An instantaneous water heater according to any one of claims 1 to 16 including on/off control valve according to any one of claims 17 to 31.

10 35. A method of constructing an instantaneous water heater for a shower, the method including: providing a water inlet, a water outlet and components defining a flow path between the inlet and the outlet, said components including an on/off valve, a flow rate control valve and a heater can; and 15 constructing said components such that, when assembled and with the on/off valve and flow rate control valve fully open, the pressure drop between the inlet and outlet is minimised.

36. An instantaneous heater constructed and arranged substantially as hereinbefore described with reference to and as illustrated by the accompanying 20 drawings.

37. A method of constructing an instantaneous water heater constructed and arranged substantially as hereinbefore described with reference to and as illustrated by the accompanying drawings.

38. An on/off control valve constructed and arranged substantially as 25 hereinbefore described with reference to and as illustrated by the accompanying drawings.