IMPROVED ELECTROLYTIC CELL

FIELD OF THE INVENTION

The present invention relates to water sanitising devices for swimming pools, spas and the like. More particularly, this invention relates to an electrolytic chlorinator cell for swimming pools, spas and the like.

BACKGROUND OF THE INVENTION

Swimming pools are popular for exercising and relaxing in but if they are to be maintained so as to provide a safe and healthy swimming environment then the pool chemistry must be controlled. This involves maintaining a consistent level of chlorine in the pool.

Chlorine is a powerful disinfectant which is effective in killing harmful organisms such as bacteria, viruses, algae and fungi. Chlorine can be introduced into the pool by regular addition of commercially available chlorine sources such as granular chlorine, chlorine tablets or liquid chlorine. This involves handling dangerous chemicals and can result in large and undesirable fluctuations in the levels achieved in the pool.

Electrolytic, or saltwater, chlorinators are a preferable solution. This requires the addition of relatively small quantities of salt (sodium chloride) to the pool and so does not necessitate handling dangerous chemicals. The electrolysis process is achieved by passing the salt water solution through an electrolytic cell which converts sodium chloride in the water into chlorine gas which, when dissolved in water becomes sodium hypochlorite (liquid chlorine).

The electrolytic cell usually consists of a housing containing the electrodes, made up of at least one titanium anode, and at least one titanium cathode coated with rare earth metals like platinum, ruthenium and iridium.

Prior art electrolytic chlorinators often do not operate at high efficiencies and so the cell may have to be run for a lengthy duty cycle each day to produce the required level of hypochlorite ions needed to keep the pool free of active pathogens. This may lessen the operating lifetime of the device which will consequently require more frequent maintenance or replacement with a new cell. These are additional costs which must be borne by the consumer.

If the electrolytic chlorinator is not operating at a sufficient performance level then, if salt levels and/or flow rates are low, an insufficient amount of hypochlorite ions may be produced by the cell to oxidise the bacteria and other impurities. This obviously has potentially severe health implications for the pool users.

Prior art electrolytic chlorinators will generally have a maximum efficiency at one particular electrolyte flow rate. Lower or increased flow rates around this optimum may result in a marked loss of efficiency. The electrolyte flow rate must therefore be monitored and maintained at this optimum value to ensure best performance.

While generally effective for their intended purpose, these prior art electrolytic chlorinators also suffer from a progressive loss in electrical efficiency due to the plating out on the cathode of dissolved alkali metal

salts, particularly calcium carbonate. Full current reversal during electrochlorinator operation must be performed to remove these calcareous deposits or the electrodes are removed from service as frequently as necessary for regular cleaning with weak hydrochloric acid or abrasion to remove the built up scale.

A typical prior art electrolytic chlorinator has three cathode plates and two anode plates, or vice versa depending on whether current reversal is applied, which sit coterminous and are spaced from one another. It has been found that large clumps of calcium deposits tend to build up on the proximal and, particularly, the distal ends of the cathode plates, in the direction of flow. These encrustations serve as a foundation for further deposition along the length of the cathodes and the electrical efficiency suffers such that removal and cleaning of the plates must be performed to maintain hypochlorite levels. Also problematic in this respect are the busbars and spacers used in prior art devices to keep the electrode plates separated. The busbars form an electrical connection between the individual anode or cathode plates but may also serve to space the plates and prevent them from coming together and short circuiting the cell. A typical prior art device will have a busbar for each of the anode and cathode. These are generally quite bulky and so the busbar for the anode may be located at the proximal end of the cell and the cathode busbar at the distal end or vice versa. The electrodes are thus held in place at each end

but, due to the length and flexibility of the electrodes, may still flex in the middle and, if they touch, cause a short circuit. To prevent this, one or more spacers are located intermittently along the length of the electrodes. The spacers may take a number of forms such as plastic clips which sit around the electrodes and are often quite large.

The effect of these bulky busbars and spacers is firstly to cause considerable disruption to laminar flow of the electrolyte solution. This in turn has a detrimental effect on the efficiency of the cell.

A further problem is that they serve to encourage the build up of alkali metal salt deposits. The plating out of these deposits mentioned earlier is much greater around the busbars and spacers as they provide a barrier to the flow path and so the deposits are less likely to be broken off and carried away by the electrolyte flow. This can result in the deposits becoming sufficiently built up to reduce the flow rate such that the cell efficiency drops dramatically or the deposits may even bridge the gap between the anode and cathode and cause the cell to short circuit.

The electrode plates must be welded, generally spot welded, to the busbars. This not only requires extra time to be spent in manufacture but also has some drawbacks in operation. The welding process inevitably damages the grain of the metal used such that the welded area is more susceptible to corrosion than the rest of the electrode. It may also be possible for water to penetrate underneath the weld and accelerate corrosion in this area.

The electrolytic chlorinator cell described in WO 2007/022572 represents an improved device with respect to the abovementioned problems. This device employs a body with parallel grooves extending longitudinally on opposite walls. The electrodes sit within and are held in spaced alignment by these grooves, thus removing the need for spacers.

This device also uses a highly polished Hastelloy cathode and a flow path which encourages laminar flow. The combined effect of the removal of the need for spacers, the polished Hastelloy surface and the improved flow is that only a thin, translucent film of alkali metal salt is found on the cathode. This is thin enough that it does not have a substantial negative effect on the electrical efficiency.

The device does, however, have a spot welded anode and cathode busbar at the proximal and distal ends of the cell respectively. Although it is an improvement over many prior art devices it would of course be desirable to further improve upon the efficiency of this device.

OBJECT OF THE INVENTION

It is an object of the invention to overcome or alleviate one or more of the above disadvantages or provide the consumer with a useful or commercial choice. SUMMARY OF THE INVENTION

In one form, which is not necessarily the only or broadest form, the invention provides for an electrolytic cell comprising a hollow body, inlet and outlet ports and an electrolyte flow path between the inlet and outlet ports,

the electrolytic cell including spaced electrodes comprising:

(a) an anode assembly having proximal and distal ends; and

(b) a cathode assembly having proximal and distal ends, wherein the distal end of the cathode assembly extends beyond the distal end of the anode assembly in the direction of flow of the electrolyte solution. Suitably, the proximal end of the cathode assembly is aligned with the proximal end of the anode assembly.

Preferably, the proximal end of the cathode assembly extends beyond the proximal end of the anode assembly in an opposite direction to the direction of flow of the electrolyte solution.

The distal end of the cathode assembly can extend beyond the distal end of the anode assembly by a distance which can be equivalent to 0.75 to 2.0 times the spacing between the electrodes.

Suitably, the distal end of the cathode assembly can extend beyond the distal end of the anode assembly by a distance which can be equivalent to 1.0 to 1.9 times the spacing between the electrodes.

If required, the distal end of the cathode assembly may extend beyond the distal end of the anode assembly by a distance which can be equivalent to 1.5 to 1.8 times the spacing between the electrodes. Preferably, the distal end of the cathode assembly can extend beyond the distal end of the anode assembly by a distance which can be equivalent to 1.6 to 1.7 times the spacing between the electrodes.

Suitably, the proximal end of the cathode assembly extends beyond

the proximal end of the anode assembly by a distance which may be equivalent to 0.75 to 2.0 times the spacing between the electrodes in an opposite direction to the direction of flow of the electrolyte solution.

The cathode assembly may have two or more spaced cathode members.

It is advantageous that the cathode assembly is fabricated as a unitary structure.

Suitably, the unitary cathode assembly may comprise an integral busbar located adjacent the electrolyte flow path. If required, the integral busbar of the unitary cathode assembly can be located in a recess in a wall of the interior of the hollow body.

The unitary cathode assembly may comprise an integral electrode terminal.

The anode assembly may have two or more spaced anode members. It is advantageous that the anode assembly is fabricated as a unitary structure.

Suitably, the unitary anode assembly may comprise an integral busbar located adjacent the electrolyte flow path.

If required, the integral busbar of the unitary anode assembly can be located in a recess in a wall of the interior of the hollow body.

The unitary anode assembly may comprise an integral electrode terminal.

Preferably, the anode assembly and the cathode assembly occupy the

electrolyte flow path within the hollow body.

In another aspect, the invention provides for a method of chlorinating water including the step of passing an aqueous electrolyte solution through an electrolytic cell comprising: (a) an anode assembly having proximal and distal ends; and

(b) a cathode assembly having proximal and distal ends, wherein the distal end of the cathode assembly extends beyond the distal end of the anode assembly in the direction of flow of the electrolyte solution. Throughout this specification, unless the context requires otherwise, the words "comprise", "comprises" and "comprising" will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

BRIEF DESCRIPTION OF THE FIGURES

In order that the invention may be readily understood and put into practical effect, preferred embodiments will now be described by way of example with reference to the accompanying figures wherein like reference numerals refer to like parts and wherein:

FIG 1A is a diagrammatic representation of an electrolytic cell according to one embodiment of the present invention; FIG 1 B is a graphical representation of the efficiency of the electrolytic cell shown in FIG 1A;

FIG 2A is a diagrammatic representation of a further electrolytic cell according to one embodiment of the present invention;

FIG 2B is a graphical representation of the efficiency of the electrolytic cell shown in FIG 2A;

FIG 3A is a diagrammatic representation of an optimised electrolytic cell according to one embodiment of the present invention; FIG 3B is a graphical representation of the efficiency of the electrolytic cell shown in FIG 3A;

FIG 4 is a cross-sectional view along the electrolyte flow path according to one embodiment of the present invention;

FIG 5 is a top view of a unitary cathode according to one embodiment of the present invention; and

FIG 6 is a perspective view of an electrolytic cell according to one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION The present invention provides for an improved and efficient electrolytic cell layout which requires less maintenance to preserve a suitable chlorine output level.

FIG 1A is a diagrammatic representation of an electrolytic cell 100 which consists of an anode assembly or anode 110 and a cathode assembly or cathode 120. The anode 110 has an upstream or proximal end 111 and a downstream or distal end 112. Likewise, the cathode 120 has an upstream or proximal end 121 and a downstream or distal end 122.

The proximal end 121 of cathode 120 is staggered by a distance 'A' past the proximal end 111 of the anode 110. Consequently, the distal end

122 of cathode 120 extends a distance 'A' beyond the distal end 112 of anode 110, in the direction of flow of the electrolyte solution. Anode 110 and cathode 120 are spaced apart by a distance 'B'.

The direction of flow of the electrolyte solution, which in the case of an electrolytic pool chlorinator is water and dissolved chloride salt ions, is represented by an arrow in FIG 1A. The directionality is from the proximal ends 111 and 121 to the distal ends 112 and 122 of the anode 110 and cathode 120, respectively.

The projected current path 130 is represented by a number of broken arrows, each of which represents the flow of electrically charged particles and thereby exemplifies the influence of the anode on the cathode. It should be appreciated that the current paths 130 shown in the FIG's are a diagrammatic representation only.

FIG 1 B is a graphical representation of the efficiency of the electrolytic cell shown in FIG 1A. This represents an improved situation over typical prior art devices. The efficiency can be seen to increase with increasing flow rate until a maximum is reached.

FIG 2A is a diagrammatic representation of a further electrolytic cell

100. In this representation the proximal ends 111 and 121 of the anode 110 and cathode 120, respectively, are aligned. The distal end 122 of cathode

120, however, extends a distance 'A' past the distal end 112 of anode 110.

Anode 110 and cathode 120 are separated by a distance 'B'.

FIG 2B is a graphical representation of the efficiency of the electrolytic

cell shown in FIG 2A. It is apparent, when compared to FIG 1 B, that this particular plate layout has a much greater efficiency at lower flow rates. The efficiency remains higher until the same maximum efficiency is reached at a high flow rate. The layout represented by FIG 2A is, therefore, a further improvement over that represented by FIG 1 A.

FIG 3A is a diagrammatic representation of yet another electrolytic cell

100 according to an embodiment of the present invention. In this embodiment the proximal and distal ends 121 and 122 of cathode 120 extend past the proximal and distal ends 111 and 112 of anode 110 by a distance 'A'. Anode 110 and cathode 120 are separated by a distance 'B'.

FIG 3B is a graphical representation of the efficiency of the electrolytic cell shown in FIG 3A. The efficiency can be seen to exceed those achieved by the electrolytic cell layouts of FIG's 1 A and 2A, as represented by FIG's

1 B and 2B, at lower and increasing flow rates. The layout of FIG 3A therefore represents an optimised layout when compared to that of FIG's 1A and 2A.

The flow rate of the electrolyte solution through an electrolytic cell can have a marked effect on the efficiency of that cell. The applicant has shown the layout of the anode 110 and cathode 120 relative to one another is a critical factor in any attempt to maximise the efficiency of the cell over a range of flow rates.

When the anode 110 and cathode 120 are completely aligned i.e. zero stagger, it is observed that as the flow rate increases the efficiency of

the cell will increase up to a maximum. Any further increase in the flow rate brings about a loss of efficiency. The current paths 130 from the distal end 112 of anode 110 may not make contact with the distal end 122 of cathode 120 at higher flow rates and so the cell efficiency drops off. FIG 1A represents an improved situation wherein a staggered arrangement of cathode 120 relative to anode 110, has been introduced. Current paths 130 are representative of the fact that at higher flow rates the charged particles leaving the distal end 112 of anode 110 may still be collected at the distal end 122 of cathode 120, thereby resulting in greater efficiency.

Whilst this represents a significant improvement over prior art devices this arrangement is still not ideal as at low flow rates the current paths 130 may be travelling at less of an angle from the anode 110 than shown in the representation. This means that charged particles leaving the proximal end 111 of anode 110 may not be collected at the proximal end 121 of cathode 120.

Further, since the proximal end 111 of anode 110 does not have a portion of cathode 120 opposite it, the electromagnetic forces from this portion of the anode are not utilised by the cathode 120 and so maximum efficiency is not achieved.

The layout shown in FIG 2A goes some way to addressing these issues to achieve a cell with further increases in efficiency over the already improved arrangement of FIG 1A. The distal end 122 of cathode 120 extends

beyond the anode 110, as with the layout of FIG 1A, and so, at increasing flow rates, higher efficiency is achieved as described previously. In this arrangement, however, the proximal ends 111 and 121 of anode 110 and cathode 120 are now aligned and so the current paths 130 coming from the proximal end 111 of anode 110 at lower flow rates, as represented, are able to be collected by the proximal end 121 of cathode 120.

This, coupled with the fact that the electromagnetic forces from the anode 110 are increased because every portion of anode 110 has a portion of cathode 120 directly opposite it, means that the efficiency of this arrangement at all flow rates, up to a maximum, is even greater than that of the arrangement in FIG 1A.

The applicant tested yet another electrolytic cell layout, as shown in FIG 3A, and found that this arrangement demonstrated an improved efficiency, even over that of FIG 2A. In the layout shown in FIG 3A the cathode 120 extends some distance past both the proximal and distal ends 111 and 112 of anode 110. As with the layouts in FIG's 1A and 2A, the extended distal end 122 of cathode 120 provides for good efficiency at higher flow rates. As discussed for FIG 2A, the fact that all of proximal end 111 of anode 110 has cathode 120 opposite it also means that the charged particles are captured at low flow rates to improve efficiency in this area.

The provision of a proximal end 121 of cathode 120 which extends past the proximal end 111 of anode 110, however, provides surprisingly large

further gains in efficiency. In large part, the reason for this is that FIG 3A represents an optimized layout for maximising the electromagnetic influence of the anode on the cathode when compared to the other layouts discussed and those in the prior art. A particular advantage of this layout is that, since cathode 120 extends beyond anode 110 at each end, high efficiencies are achieved at both low and increasing flow rates. This is particularly useful when increasing flow rates are occasionally employed to reduce scale build up on the electrodes. The influence of the anode on the cathode has been referred to in terms of the electromagnetic forces generated. The applicant has discovered that maximising this effect is surprisingly beneficial in terms of improving the efficiency of the electrolytic cell and reducing scale build up.

During experimentation the applicant observed that the area of cathode which receives current from the anode is greater than the area of anode which supplies that current. This effect is partly represented by the current flow 130 shown by broken arrows in FIG 3A. This influence does not only extend in the direction of flow, however, but rather it can be thought of as a cone of electromagnetic influence on the cathode extending from each point source on the anode. For the sake of clarity this influence is not demonstrated in all directions on FIG's 1A to 3A. If some of this electromagnetic influence extends beyond the cathode 120 at either the proximal end 121 or distal end 122 then its potential chlorine-generating

effect is lost and the efficiency of the cell is sub-optimal.

This effect of an area of influence on the cathode 120 being greater than the size of the anode 110 opposite it was observed by viewing the pattern of calcium salt deposit build up on cathode 120. In these tests anode 110 was masked apart from a specific area which was left exposed and, after normal operation, the pattern of calcium build up on cathode 120 due to the influence of the exposed portion of anode 110 was observed as a thin translucent film. The pattern of the deposit observed corresponds to the active area of cathode 120 which is being influenced by anode 110. In all experiments the size of the area of calcium salt build up on cathode 120 was greater, in all dimensions i.e. length and breadth, than the size of the portion of anode 110 which was left exposed. This supports the findings shown in FIG's 1 B, 2B and 3B of increasing efficiency as cathode 120 becomes staggered past both the proximal 111 and distal 112 ends of anode 110.

As the area of cathode affected by the anode was greater than the size of the anode in all dimensions this means the anode may be sized down in comparison to the cathode and still have an influence over the entire cathode area. Although in the embodiments shown in FIG's 1A-3A the cathode is described as extending past the anode at its distal and, in FIG 3A, its proximal end, it can be beneficial to have the cathode extend beyond the anode in all dimensions, that is the all of the borders of the cathode extend beyond the borders of the anode.

In this manner the same efficiency is achieved as the same area of cathode is still being influenced by the anode and, hence, is producing chlorine but savings can be made as less metal is used to produce the anode. The metals used for manufacturing the anode can be expensive and so this arrangement allows efficiency to be maintained while lowering manufacturing costs.

The main factor which was found to influence the area of the calcium film deposit which formed on cathode 120 was the separation of the plates i.e. the distance "B" shown in FIG's 1A, 2A and 3A. The flow rate of the salt solution did not have a strong impact upon the extent of this influence.

The applicant has shown that for maximum efficiency cathode 120 should be staggered far enough past both the proximal 111 and distal 112 ends of anode 110 to receive the current from all parts of anode 110. This creates a maximised active region for chlorine production. A cell with coterminous i.e. equal sized and aligned cathode 120 and anode 110 will have a sub-optimal efficiency due to current losses.

In one example the applicant found that when a 15 mm overlap of cathode in relation to anode at both the proximal and distal ends was used, when using a 7mm plate separation, this resulted in a gain of 14% more active cathode area being available for chlorine generation when compared to a cell with coterminous i.e. completely aligned cathode and anode.

A further example showed that when a 15mm by 15mm square portion of anode was exposed it resulted in a zone of influence on the

cathode of approximately 45mm by 45mm square.

The distal end of the cathode can extend past the distal end of the anode by a distance which is less than the spacing between the electrodes. For the reasons given above, however, it is preferred that the cathode extends past the distal end of the anode by a distance which is equivalent to or greater than 0.75 times, i.e. 75% of, the spacing between the electrodes. The same is true of the proximal end of the cathode extending past the proximal end of the anode.

The applicant has shown that the optimum value for cathode 120 to extend past the distal end of anode 110 is related to the plate spacing 'B' and the flow rate of the electrolyte solution. A minimum distance for this extension, equal to the spacing between the electrodes, is preferred for a notable increase in cell efficiency to be produced. A typical working range to maximise efficiency would be an extension of the distal end of the cathode beyond the distal end of the anode equivalent to 0.75 to 2.0 times the spacing between the electrodes.

Preferably, the distal end of the cathode extends beyond the distal end of the anode by a distance equivalent to 1.0 to 1.9 times the spacing between the electrodes. More preferably, the distal end of the cathode extends beyond the distal end of the anode by a distance equivalent to 1.5 to 1.8 times the spacing between the electrodes. Even more preferably, the distal end of the cathode extends beyond the distal end of the anode by a distance equivalent to 1.6 to 1.7 times the spacing between the electrodes.

The stated ranges for the extension of the distal end of the cathode past the distal end of the anode also apply for the extension of the proximal end of the cathode past the proximal end of the anode in the opposite direction to the direction of flow. Due to the influence of the direction of flow on the charged particles, however, it may not always be necessary for the proximal end of the cathode to extend past the proximal end of the anode by quite the same distance as for the distal ends. The electromagnetic effect discussed previously, however, will often mean that the same optimal extension distance as for the distal ends may be useful anyway. The applicant has found that an optimal A/B ratio is 5:3 (i.e. between

1.6 to 1.7 times the plate spacing) for a given flow rate e.g. if the plate separation is 6mm (distance "B") then the cathode should extend past the anode (distance "A") by 10mm at both the proximal and distal ends to achieve maximum efficiency. It should be appreciated that the actual efficiency achieved will also depend to an extent on the flow rate chosen but plate separation has been found to be the most important factor to consider for optimisation.

It may also useful, as mentioned, to have the anode assembly not extend past the cathode assembly i.e. the cathode extends past the anode in all directions. Therefore, if all borders of the cathode extend past the borders of the anode, as described previously, then the distance of the extension relative to the spacing between the electrodes should be as described above for the proximal and distal ends of the cathode.

During testing and quantification of the build up of calcium salt deposits on cathode 120 the inventors have also observed an additional important benefit of the staggered cathode arrangement. In prior art electrolytic cells cathode 120 and anode 110 are coterminous and it is observed that large and irregular clumps of deposited material would appear at the proximal 121 and distal 122 ends of cathode 120. The appearance of these large deposits would then serve as a foundation for further build up along the entire length of cathode 120. This results in a decrease in efficiency of the cell and hence a drop in chlorine production unless cathode 120 is removed for regular cleaning.

The device described in WO 2007/022572, which disclosure is hereby incorporated by reference, presented one solution to this problem by removing the need for spacers, having highly polished Hastelloy cathode plates and maintaining a velocity cleaning effect by encouraging a laminar flow path.

However, the applicant has found that when cathode 120 is staggered past anode 110 such that particularly the distal 122 end and, potentially, the proximal 121 end of cathode 120 extend beyond the electromagnetic influence of the distal 112 and proximal 111 ends of anode 110, then the appearance of the bulky deposits on the edges of cathode 120 are also avoided in this manner.

The influence of the anode should not extend all the way to the proximal and distal edges of the cathode. This is an optimal arrangement. It

has been found that in this situation only a smooth and thin, translucent layer of deposition occurs on the flat surface of cathode 120. This maintains the efficiency of the cathode over a longer time span and helps keep chlorine production at the desired level. The lower maintenance required in this situation clearly benefits the consumer. If the cathode was extending beyond the anode in all directions then this finding would be applied to all borders of the cathode to minimise deposition on all edges.

These tests were carried out in an electrolyte solution with an artificially high calcium carbonate content in the order of 1000 ppm. Most pools would have levels of 60 ppm up to a maximum of about 450 ppm calcium carbonate. Even in this environment of elevated calcium carbonate levels the present device showed minimal deposition on the cathode.

The advantages of the device disclosed in WO 2007/022572, as mentioned above, can thus be combined with the staggered cathode arrangement represented by FIG 3A to produce a device which uses a number of features and electromagnetic effects to reduce calcium and other alkali metal salt deposits to a minimum while at the same time maximising the efficiency of the cell. The very thin film which does plate out seems to come to equilibrium i.e. it does not build up further and is so thin as to not noticeably influence the efficiency of the cell.

Since the active chlorine producing region of the electrodes has been optimised by the applicant by the use of the staggered cathode arrangement it is important to take full advantage of this improvement by maximising the

amount of electrolyte solution which flows through this active region and hence, optimise chlorine production. To this end the flow path effect disclosed in WO 2007/022572 will be employed.

This involves confining the electrolyte flow path so that all flow passing into the electrolytic chlorinator through an inlet must pass through a hollow interior which is substantially occupied by the electrodes before passing out through an outlet. The interior may, in theory, take any shape which encourages laminar flow. In practice, however, the cross-sectional shape of the hollow interior of the cell body will be limited by the number, size and arrangement of the electrodes.

One embodiment of this arrangement is shown in FIG 4 wherein the flow path is formed by a body 140 which forms a rectangular hollow interior 141 in cross-section. A series of longitudinal ridges 143 extend into the hollow interior to form longitudinal grooves 142 into which the electrodes are seated. The cathode assembly 120, in the embodiment shown, has three spaced cathode members or plates represented as clear rectangles while the anode assembly 110, in the embodiment shown, has two spaced anode members or plates represented by rectangles containing diagonal lines. As the electrolyte solution flows through the hollow interior it must pass over the active region of the cell and so chlorine production is maximised. As can be seen in FIG 4 substantially all of the electrolyte solution is exposed to the active region of the cell.

It should be appreciated that although in the embodiment shown in

FIG 4 the electrode plates are located in adjacent longitudinal grooves, this may not necessarily be the case. A larger number of grooves may be provided and the plates may only be located in every second or third groove, for example. The arrangement chosen will depend upon the width of the grooves and the spacing which is desired between the cathode and anode members. This design allows flexibility in the arrangement of the cell, particularly in relation to electrode member spacing which is a critical factor in optimising efficiency.

The body 140 defines the flow path and will be shaped to encourage laminar flow. This uses the velocity cleaning effect to produce a self cleaning device as described in WO 2007/022572 which requires very little maintenance.

Clearly any object which sits within the flow path will serve to disrupt the laminar flow and hence lower efficiency and lead to increased build up of calcium and magnesium salts. The present design therefore incorporates a number of further features which result in less obstruction to smooth flow of the electrolyte solution.

Typical prior art chlorinators have a busbar attached to both the anode and cathode at their distal or proximal ends and spacers in between. As the electrodes extend some distance longitudinally within the cell, the busbar at the distal end of the anode and/or cathode not only forms an electrical connection but also helps maintain spacing between the electrodes to prevent electrical shorting. The busbars and spacers sit within the flow path

and can serve to catch calcium deposits from the flow path and encourage their build up.

The cell design of WO 2007/022572 obviates the need for spacers between the electrode members by providing parallel grooves extending longitudinally on opposite walls but still uses a busbar at the distal end of the cathode. Although this device has a minimal amount of calcium salt deposition because of its advantages as previously described, the busbar on the cathode may collect any small pieces of the deposit which are washed off the electrodes by the velocity of the electrolyte flow. It also provides a relatively small but still significant disruption to the flow path.

To overcome the serious deficiencies of typical prior art devices and provide an improvement even over the useful arrangement described in WO 2007/022572, in a preferred embodiment of the present invention a cathode assembly which is cut in one piece from a single sheet of metal and then folded over to give the desired number of aligned cathode plates, is used. In other words the cathode assembly is cut out or fabricated as a unitary structure. The need for a separate busbar is thereby obviated.

A one piece or unitary cut out cathode assembly according to one embodiment of the present invention is shown in Fig 5 which shows the cathode after having been cut out and before folding. In this embodiment the cathode 120 is cut to present three cathode members or plates 123A-C. They are held together by a small integral busbar 124. The integral busbar is much smaller than the busbars which are typically welded onto the individual

cathode plates and so occupies less of the flow path. Its size also allows it to sit at the proximal end of the cell, if required, and so the need for a distally located busbar is obviated.

Using a unitary cathode assembly provides a number of advantages both in manufacturing and operation. A major advantage is that a unitary cathode means less spot welding is necessary during manufacture of the electrolytic cell. Not only does this save in labour costs but since the welded areas are particularly prone to corrosion, minimising the need for them can increase the operational lifetime of the electrolytic cell. This is particularly important for electrodes manufactured from iron containing alloys, such as Hastelloy C-276 and other Hastelloy metals.

The unitary cathode assembly cut out shown in FIG 5 can be conveniently folded up, in more than one way, to give the final unitary cathode for attachment to the electrolytic cell. In one embodiment, plate 123A is firstly folded underneath plate 123B as viewed from above in FIG 5. It is then bent to form a T-shape with plate 123A projecting into the page as viewed in FIG 5. Plates 123B and 123C are then folded to sit either side of and be substantially coterminous with plate 123A. As viewed in FIG 5 this would leave the long part of the integral busbar region labelled 124 lying in the plane of the paper while all three plates project into the page.

Alternatively, plate 123A is firstly folded to form a T-shape with plate 123A projecting directly into the page as viewed in FIG 5. Plate 123A is then folded back 180° to project directly out of the page towards the viewer as

seen in FIG 5. Plates 123B and 123C are then folded upwards to be aligned with plate 123A. This method of folding has the advantage that the plates are not folded onto one another and so scratching of their surfaces by accidental contact is less likely. The unitary cathode assembly may be punched out, laser cut or otherwise cut out of a single piece of metal. Clearly, the embodiment shown in FIG 5 is not the only possible cut out design for a unitary cathode. The design of the cut out will change if more or less cathode plates need to be presented. For example, it may be desirable to only have two cathode plates presented and so plate 123A, shown in FIG 5, would not be present and plates 123B and 123C would simply be folded towards one another to give the final unitary cathode. Other ways of cutting out a unitary cathode and of folding it could be ascertained by a person skilled in the art in light of the present disclosure. When this unitary cathode design is combined with the flow path design of WO 2007/022572 any turbulence which may have been present due to the cathode busbar is further reduced by the provision of this unitary cathode with an integral busbar which, in combination with the longitudinal grooves discussed earlier, removes the need for a separate busbar at the distal end of the cathode.

Further improvements in laminar flow are gained when the cathode integral busbar is located adjacent the flow path or, preferably, within a recess in one of the walls defining the flow path. Although not explicitly

shown in FIG 4 this recess can be formed by the longitudinal ridges 143 only beginning a short distance into the interior of the body defining the flow path. This means there is an initial flat surface on the opposite walls of the interior of the body defining the flow path before the ridges are encountered. As this flat surface is clearly below the level of the longitudinal ridges then the cathode integral busbar can sit flush against the interior surface and by doing so be effectively removed from the flow path.

FIG 6 shows the arrangement of an electrolytic cell according to an embodiment of the present invention. Although in the embodiment shown in FIG 6 the cathode integral busbar 124 sits at the proximal end 121 of the cathode assembly it will be appreciated that this is not the only possible arrangement. The integral busbar may be located anywhere along the length of the cathode assembly, such as the middle portion, and may be designed such that it is incorporated into one of the walls of the body defining the flow path. In this way it would also be removed from the flow path to reduce turbulence. The design of the unitary cut out will clearly decide where the integral busbar is located and hence, how it is kept out of the flow path.

The anode assembly shown in the embodiment represented in FIG 6 has a separate anode busbar 114 as the electrical connector joining the individual anode plates 113A and 113B. It is clearly within the scope of the present disclosure, however, for the anode to also be a unitary design. This would remove the need for yet another busbar and would again provide the benefits discussed of preventing calcium deposits being caught, improving

laminar flow, simpler manufacture and longer lifetime due to less spot welding and hence corrosion.

The anode assembly could be manufactured and folded in a similar manner to the cathode assembly. For example, in the embodiments shown only two anode plates are used and so a simple cut out design whereby two anode plates are joined by an integral busbar and can be folded up to be aligned with one another would be appropriate.

If a unitary anode assembly and cathode assembly are used then only one spot weld each is required to connect the unitary cathode and anode to their respective terminals. The drawbacks of welding were mentioned before and it should now be clear how a unitary electrode and the use of the longitudinal grooves to remove the need for distal connecting busbars greatly reduces the amount of spot welding required and so the operational lifetime of the cell. The cathode assembly is preferably made from Hastelloy and the anode assembly from titanium. These are not the only materials suitable for manufacturing the anode and cathode, as would be understood by a person skilled in the art. The arrangement of the anode and cathode plates whereby the cathode extends beyond the anode at both the proximal and distal ends is clearly visible in FIG 6. In the embodiment shown the other edges of the anode and cathode are aligned. However, as described earlier, it may be desirable to down size the anode in both these dimensions so that the cathode extends beyond all four borders of the anode. The benefits of having

a staggered cathode assembly as described herein may then be increased even further and savings are made in the manufacture of the anode.

The connections of the electrodes to their terminals supplying the power are also shown in FIG 6. The electrode terminals extend from end cap 150 which also houses circuit isolator 154. The anode terminal, which is mostly obscured, sits in a waterproof socket 151. The connection to the cathode is via a rod-like terminal 153 which sits within waterproof socket 152. The cathode rod-like terminal would be welded to one of cathode plates 123A-C. The anode busbar 114 can be seen to be connected to both anode plates and a welded connection would be present at 115 as well as beneath plate 113B.

Although in the embodiment described in FIG 6 the anode and cathode terminals are welded to a plate of the respective electrodes it is desirable to avoid this welded connection for reasons of limiting corrosion already described. Hence the design of the unitary cathode and/or anode assemblies described herein may be modified to include an extension which forms the electrode terminal. In FIG 5 the potential for this connection on the unitary cathode is indicated by extension 125. If it was desired to make a unitary electrode assembly with an integral terminal then clearly this extension could simply be made larger and of a suitable shape, e.g. rolled to form a pin connector, to form the necessary electrical connection. This further reduces the number of spot welds required in the cell and so lowers manufacturing costs and improves resistance to corrosion.

The cathode plates 123A-C can be seen to extend past both the proximal and distal ends of the anode plates 113A and 113B thereby presenting the benefits of a staggered cathode arrangement as discussed.

Circuit isolator 154 is a safety feature to automatically turn off the electrolytic chlorinator if the water level in the pool should drop and the cell runs dry. When the cell is under water the circuit is closed but if it runs dry the circuit isolator opens the circuit and the power is automatically turned off.

This is an important safety feature since, if the cell was running dry but the power was not turned off, hydrogen and oxygen production would continue without the electrolyte flow to continually remove them from the cell. This can lead to a build up of flammable gases and, potentially, an explosion.

The cell may run dry because the water level in the pool drops or because the pump fails. In the latter case there may be electrolyte solution in the cell initially but, because the cell is still working, hydrogen is produced without being removed by the flow. As the hydrogen builds up it forces the water out of the cell and the circuit isolator 154 will switch the cell off before the hydrogen levels build to dangerous proportions.

It is envisaged that the disclosure of WO 2007/022572 could be combined with the staggered cathode assembly and unitary cathode and/or anode assemblies of the present invention to produce a highly efficient, self- cleaning, low maintenance and long operational lifetime electrolytic chlorinator. The cell layout represented in FIG 3A should be used as this represents an optimized layout.

This would provide an electrolytic cell with all the advantages of the device of WO 2007/022572 as described above but also with an increased efficiency over a range of flow rates due to the extension of the cathode past the anode in both upstream and downstream directions. When this is combined with the unitary cathode and/or anode an electrolytic cell with a number of distinct advantages over prior art devices is achieved.

The applicant has identified a need for an electrolytic chlorinator cell which has demonstrated a high efficiency when in use and which requires less maintenance to keep the cell performance at acceptable levels. The present invention provides for an electrolytic cell layout which results in a high efficiency at both low and increased flow rates due to the arrangement of the electrodes. The staggered arrangement of the cathode also maximizes the electromagnetic force of the anode on the cathode and provides for efficient hypochlorite production. Further efficiency is gained by the use of a unitary cathode and/or anode which obviates the need for a separate busbar and so improves the laminar flow over the active chlorine producing region of the cell.

The unitary cathode and/or anode assemblies removing the need for a separate busbar also provides savings in labour as less spot welding is necessary. This provides further advantages in greatly reducing corrosion in these areas and so increasing the lifetime of the electrodes.

The disclosure herein also provides for a method of chlorinating water including the step of passing an aqueous electrolyte solution through an

electrolytic cell comprising:

(a) an anode assembly having proximal and distal ends; and

(b) a cathode assembly having proximal and distal ends, wherein the distal end of the cathode assembly extends beyond the distal end of the anode assembly in the direction of flow of the electrolyte solution. This method is useful in maintaining a safe environment for bathers in pools, spas and the like by keeping chlorine levels within an appropriate range to thereby destroy potentially harmful microorganisms as hereinbefore described. It will be appreciated by the skilled person that the present invention is not limited to the embodiments described in detail herein, and that a variety of other embodiments may be contemplated which are, nevertheless, consistent with the broad spirit and scope of the invention.