BACKGROUND OF THE INVENTION This invention relates to water tanks, and particularly to water tanks for use in rural properties for storing large quantities of water. Since the advent of the corrugated iron water tank over one hundred years ago, there has never been a "perfect" water tank; all of the several types available have a number of disadvantages.

Curved and corrugated galvanised iron tanks are probably the oldest tanks in general use in Australia and have served the population well over the years, giving the consumer as clean a drink of water as was likely to be found anywhere. Figure 1 shows such a tank 1, formed of a number of curved corrugated sheets 2 of galvanised iron riveted together. However, the water does contain traces of zinc picked up from plain galvanised roofing material 3 and the tank walls. Although these tanks are still made in Australia, opposition is growing, and for good reason. Old fashioned tankmakers still use lead based solders to seal them, which means the water is in contact with lead. This is considered a definite health hazard. Another disadvantage is the fact that modern coated roofing materials produce no salts to modify the water as it flows over the roof and into the tank, with the result that galvanised tanks now suffer the ravages of electrolysis, a phenomenon which severely shortens the life of the tank. Also, because of their fully made up and ready to use configuration, these tanks are enormously expensive to freight, which usually has to be undertaken by the manufacturer, as any attempt to use other carriers almost always results in serious damage because of the tanks delicate nature.

Aquaplate sheeting is produced for the tankmaking industry by B.H.P. Steels Coated Products Division, and represents a great leap forward in water tank technology. No longer does the consumer have to put up with tanks that rust out or ones that pollute their water.

Aquaplate is the same galvanised iron previously mentioned but has a membrane of food grade polymer bonded to one side of the sheet for use in the walls of the tank and to both sides of the sheet for use in the bottoms. This membrane protects the walls of the tank from corrosive attack by the water, and protects the water from the entry of any metals from the tank itself. The underside of the bottom is also protected from attack from any material that the tank may be sitting on.

The polymer used to make aquaplate complies with Australian Standards Code AS 2070 "Plastics materials for food contact use".

Lead based solders have also been eliminated in the sealing of these tanks as clean non-toxic silicone rubber sealants are now available to the tank industry at reasonable cost.

The only disadvantages suffered by aquaplate tanks are that 1n practical terms they are only feasible for factory based manufacture up to 22,500 litres capacity. Any attempt to manufacture on site would be so costly as to be impractical. As time passes more and more councils are demanding a minimum of 90,000 litres of water storage for rural blocks. Also this type of tank suffers from the same freight limitations as previously mentioned. These disadvantages are caused by old fashioned design which the tank industry generally seems content with.

Galvanised steel kit tanks use flat galvanised steel walls which have a profile pressed into them by the manufacturer to give the tank some strength. There are several manufacturers of kit tanks, who all use a very similar design which appears to have been inspired by above ground swimming pools.

They are manufactured in small panels, about 2.100 metres x 1.200 metres, which are-then supplied to the consumer 1n completely knocked down form. No pre-assembly of any of the components of the tank Is undertaken by the manufacturer at all. Even large tanks can be carried on a small one tonne trailer.

In this scenario, the manufacturer has taken everything for himself, the small panel design to enable high volume mass production, and the freight savings, because the tank can be packed in such a small area. He has left the consumer with all the work, a job that requires the skills of at least an advanced handyman. After inserting a thousand or so bolts in the tanks, sealing 1s achieved by placing a giant plastic bag inside the tank body, an idea which has caused many problems in the field because of sweating that occurs between the plastic bag and the galvanised tank walls, rusting them out. Some manufacturers offer no more than a blanket of shade cloth for a tank top, which is no top at all. Those who are offering steel tops are offering ones of very poor design that do not seal the tank properly, which allows the entry of vermin into the tank.

The concrete industry has successfully produced a tank that will last a lifetime but the water quality Is very poor, especially in the

first year or two when lime leaches into the water spoiling Its quality.

After this, because of the ideal conditions inside a concrete tank, algae starts to grow, the porous walls providing a superb surface for it to cling to, and the nutrients 1n the water food for 1t to feed on. The life cycle of algae pollutes the water further, in that dead algae falls to the bottom of the tank where 1t Is attacked and decomposed by bacteria. It is during this process that the water is robbed of valuable oxygen, making 1t undesireable to most people.

The walls of a concrete tank offer no burning heat generated by the sun to kill off any algae that attempts to grow, as is the case with steel tanks, so this polluting process continues whilst ever the tank is in service.

Many councils use concrete water towers or tanks in their town water reticulation systems, but there are a couple of significant differences between these and concrete tanks in a domestic situation.

Firstly, the water in these towers is not captive, it moves Into and out of the tank fairly quickly because of the large volumes of water used in a town supply. Also most councils treat the water to prevent the growth of algae in the first place. Another major fault in concrete tanks is their high failure rate through cracking. Cost pressures in the Industry have caused a general lack of sound engineering practices, making the installation of a concrete tank risky business.

For Instance, a 250,000 litre concrete tank which has to withstand the forces placed upon it by 250 tonnes of water is installed in most cases with no foundations! This 1s a recipe for disaster in the construction of a vessel as rigid as this because they are already prone to cracking because of the poor engineering previously mentioned. Uncontrolled curing rates also play their part in the early failure of concrete tanks.

Flbreglass reinforced plastic tanks are a relative newcomer to the tank industry, having appeared 1n commercial numbers only in the last ten years. Although they are being sold in the expectancy of being for life, in reality their life expectancy 1s in the region of six to ten years. This assessment is made on the basis of experience 1n the replacing of flbreglass tanks with aquaplate tanks; all of the tanks replaced so far have been 1n the six,to ten year age bracket.

These failures are caused in the main by the plastic epoxy resin breaking down because of constant exposure to ultraviolet light; this situation being exacerbated by the small wall thickness of these tanks. If the wall thickness was substantially Increased then their life would increase accordingly, but this would price them out of the market. A phenomenon similar to osmosis also plays a part 1n the early failure of plastic tanks. Water enters the laminate through hairline cracks 1n the plastic gelcoat which then expands and creates pressure within the material and forces delamination. Furthermore, fibreglass tanks still have to prove their ability to store drinking water meant for human consumption without polluting it with chemicals from the tank walls. Epoxy resins are very toxic chemicals, their toxicity decreases as curing progresses but, the question still remains, are they safe? The fibreglass Industry does not think so because they coat the Inside of the tanks meant for drinking water with another chemical to prevent any direct contact with the epoxy resins in the tank walls, but it is not likely that this coating will remain In place indefinitely under water.

The fibreglass strands used to reinforce the resins in the tank walls likewise have serious questions to answer as to the effect they may have on the health of people ingesting any free glass fibres that may be in the water they drink. Only recently, some very serious questions have been raised about the problems of Inhaling glass fibre dust when installing ceiling insulation. It is possible, therefore, that water tanks made of reinforced epoxy resins offer the consumer nothing in the way of safequarding their health, or value for money.

This completes the review of the water tanks presently available to the Australian market.

Water is one of the most important commodities to rural dwellers. Without sufficient quantities of water their quality of life is severely diminished. Equally, the water storage vessel ranks as a most Important Installation, 1t has to be absolutely reliable, any rust holes or cracks can let a years supply of water run out overnight. It also has to be made of clean, non-polluting materials 1n order to safeguard the health of the user and his/her family. Another very important necessity 1s durability, water tanks that have to be replaced are inconvenient and an unnecessary financial burden. Value for money is another desirable attribute that a water tank must have, ideally it would be produced 1n a

high volume mass production situation and be of a suitable design that would enable it to be transported economically to the site and then be erected by completely unskilled labour 1n less than a day.

BRIEF SUMMARY OF THE INVENTION Accordingly, in one aspect of the invention, there is provided a tank module comprising a frame having a pair of vertical generally elongate members connected by a pair of horizontal, generally elongate members, each of the vertical members having a first longitudinal flange extending towards the other vertical member and each of the horizontal members having a first longitudinal flange extending towards the other horizontal member, each of the members also having a second flange extending substantially perpendicularly to the first flange, and one or more corrugated sheets being mounted between the members of the frame in a watertight manner. In a preferred embodiment, the pair of horizontal members are curved longitudinally. Preferably, the second flanges of the horizontal members extend inwardly towards the centre of the radius of curvature of the horizontal members. The corrugated sheets are preferably mounted to the first flange of the members between the second flange of the members. Preferably, the corrugated sheets are mounted by means of rivets and a sealing compound, such as si1cone gel, is provided between the members and the sheets. The corrugated sheets are preferably covered with sheet plastics material, such as food grade polymer, on an inner side thereof. Preferably, the corrugated sheets are of iron, which can be galvanised, if desired.

According to a second aspect, the Invention provides a water tank comprising a plurality of tank modules as described above arranged at least side by side to form a perimeter of the tank and having adjacent second flanges of adjacent modules connected together, a plastics sheet of a size to fit within the perimeter of the tank being sealed to the second flange of the lowermost horizontal members of the plurality of modules, and a tank top being mounted to the second flange of the uppermost horizontal members of the plurality of modules.

If desired, more than one row of modules can be arranged on top of each other with adjacent second flanges of vertically adjacent modules being connected together. Preferably, the modules are connected together by bolts passing through corresponding holes in the second flanges of the members.

In a preferred embodiment, the plastics sheet, which is preferably of heavy duty food grade polymer, is sealed to the second flange of the lowermost horizontal member of the plurality of modules by clamping the plastic sheet between a pair of cooperating snap fitting extrusions, a first of the extrusions being mounted to the second flange of the lowermost horizontal member after the plurality of modules are connected together and the other of the extrusions being snap fitted thereto after the perimeter portion of the plastics sheet is laid over the first extrusion so that the plastics sheet is clamped between the two extrusions.

In a further preferred embodiment, the first extrusion is itself snap fitted to the second flange of the lowermost horizontal members of the plurality of modules, the second flange being provided with an upstanding step portion, over which a corresponding toothed flange of the first extrusion Is snap fitted. Alternatively, the first extrusion can be riveted or otherwise directly mounted on the second flange.

The tank top is preferably sealed to the second flange of the uppermost horizontal member of the plurality of modules by providing a compressible seal between the tank top and the second flange, the tank top being bolted to the second flange to compress the seal therebetween. The tank top can be either substantially flat or of conical shape.

The substantially flat tank top is preferably formed of corrugated sheeting. The tank top is preferably cut to shape from flat sheets of galvanised iron and then corrugated. The conical tank top is preferably formed of a plurality of generally sector-shaped, flat sheets mounted between a plurality of first elongate members extending radially from a first centre plate to the second flange of the uppermost horizontal members of the plurality of modules, the first centre plate being connected by an adjustable spacing member to a second centre plate, a plurality of radially extending second elongate members being connected between the second centre plate and the second flange of the uppermost members of the plurality of modules so that, by adjusting the adjustable spacing member, the spacing between the first and second centre plates can be varied, thereby altering the tension on the first and second elongate members between the centre plates and the second flange to which they are connected.

This will tension the upper portion of the tank to strengthen its structure. Preferably, the second elongate members are threadably

connected to the second flange so that the tension of each second elongate member can be individually adjusted. Furthermore, the first elongate members are preferably substantially flat members extending over an end of a threaded bolt screwed through the second flange and being bolted to the second flange, the threaded bolt thereby adjusting the tension in the flat members by being screwed into and out of the second flange.

Thus, according to a third aspect of the invention, there is provided a tensloning apparatus for a generally circular structure, comprising a plurality of first elongate members extending radially from a first centre plate to the generally circular structure, the first centre plate being connected by an adjustable spacing member to a second centre plate, a plurality of radially extending second elongate members being connected between the second centre plate and the generally circular structure, so that, by adjusting the adjustable spacing member, the spacing between the first and second centre plates can be varied, thereby altering the tension on the first and second elongate members between the centre plates and the generally circular structure.

According to a fourth aspect of the invention there is provided a method of constructing a water tank comprising the steps of: arranging a plurality of modules of the type described above to form a perimeter of the tank; connecting the adjacent second flanges of vertical members of adjacent modules together; sealing a sheet of plastics material to a second flange of the lowermost horizontal members of the plurality of modules; and mounting a tank top to the second flange of the uppermost horizontal members of the plurality of modules.

Preferably, the step of sealing comprises: mounting a first extrusion to a second flange of the lowermost horizontal members of the plurality of modules; positioning a peripheral portion of a circular plastics sheet over the first extrusion; and snap fitting a second extrusion into a cooperating portion of the first extrusion so as to clamp the plastics sheet therebetween.

It will thus be apparent that 1n the present invention flexibility of design 1s an advantage that will be of enormous benefit to the consumer but that hitherto has been totally overlooked.by the water tank

industry. A tank that can be stacked one upon another will have the obvious benefits of cost and space saving to the purchaser. A person could, for instance, buy one tank then at some time in the future buy a second tank and place it on top of the first tank. The cost saving here comes from the fact that the person only has to buy the barrel of the second tank as he has already bought the top and bottom with the first tank. This will produce a very significant saving of around thirty percent on the second tank.

Furthermore, the present invention enables mass production of big tanks that can be transported all over Australia by conventional means. This produces cost savings to the manufacturer and consumer alike.

BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the invention will now be more fully described, by way of example, with reference to the drawings, of which: Figure 1 is a sketch of a known water tank formed of a number of sheets of corrugated steel ;

Figure 2 is a sketch drawing of a water tank according to one embodiment of the present invention;

Figure 3 is an external perspective view of one module used in the construction of the water tank shown in Figure 2;

Figure 4 is an internal perspective view of the module of Figure 3; Figure 5 is a schematic cross-sectional view on line V-V of Figure 2;

Figure 5A is a schematic cross-sectional view similar to Figure 5, but of an alternate embodiment;

Figure 5 is a schematic cross-sectional view on line VI-VI of Figure 2;

Figure 7 is a schematic cross-sectional view on line VII-VII of Figure 2; Figure 8 is a schematic cross-sectional view similar to Figure 5 and showing the bottom of the tank;

Figure 9 is a schematic cross-sectional view through a tensionlng means used to support the top of the tank of Figure 2;

Figure 10 is a part cutaway plan view of the tank of Figure 2; Figure 11 is a schematic cross-sectional view on line XI-XI of Figure 10; and

Figure 12 is a schematic cross-sectional view similar to a portion of Figure 9, but showing an alternate embodiment.

-SI- DETAILED DESCRIPTION OF THE DRAWINGS As described above, Figure 1 shows a conventional known water tank

I formed of a number of overlapping sheets 2 of horizontally corrugated steel. The sheets are fixed together by rivets 4 and the complete tank, including the top 3 and the bottom is constructed by the manufacturer an then transported whole to the customer. Clearly, there is an upper limi on the size of tank which can be economically transported either by rail or road.

One embodiment of the present invention is shown in Figure 2, wher a water tank 5 is shown constucted of a number of modules 6. Each modul 6, as best shown in Figure 3 and 4, consists of a frame 7 and a number, in this case three, of horizontally extending sheets 8 of corrugated steel. The sheets 8 are covered on one side by food grade polymer and are preferably the sheets manufactured by BHP Steel under the name Aquaplate.

The frame 7 comprises a pair of substantially vertical longitudina angle irons 9 having two perpendicular flanges 10 and 11. A first of th flanges 10 extends substantially transversely to the frame 7 so as to extend in a radial direction of the complete tank. The radial flange 10 is provided with a number of apertures 12 spaced at intervals along its length.

The two vertical angle irons 9 are joined together to form the frame 7 by two substantially horizontal angle irons 13. The vertical an horizontal angle irons 9 and 13 are joined together by cutting appropriate indents and welding together, as shown at 14. The horizonta angle irons 13 are curved in their longitudinal direction so as to have radius of curvature appropriate to the size tank which is to be constructed from the modules. The horizontal angle irons 13 have two flanges 15 and 16, a first one of which 15 extends transversely to the frame so as to extend in the same direction as radial flanges 10 of angl irons 9 and is optionally provided with a number of spaced aperture hole 17, similar to holes 12 in radial flanges 10 of vertical angle irons 9.

The other flanges 11 and 16 of the angle irons 9 and 13 are arranged to extend inwardly in the plane of the frame 7 on the outer sid as compared to the curvature of the frame 7. Thus, these outer flanges

II and 16 He on the outside of the tank when it is constructed. The completed frames 7 are galvanised before the sheets 8 are mounted theret

As can be seen in Figure 4, the corrugated sheets 8 are curved wit the corrugations running horizontally to the same curvature as the frame 7. The sheets are fixed together along their overlapped portions 18 by means of 4mm monel pop rivets 19, and are also fixed to the outer flange 11 and 16 of angle irons 9 and 13 by means of similar 4mm monel pop rivets 20 and sealed thereto using silicone 21. Silicone is also used t seal the overlap between two sheets, although the sheets may, alternatively be joined using a standard "lockseam". All rivet heads inside the tank are also covered with silicone. It will be appreciated that the curvature of the horizontal angle irons 13 will depend on the radius of the tank to be constructed and on the number of modules to be used. For example, a convenient size for the modules is 2.7 m around the curved face and 2.3 high. The module dimensions do not necessarily change with tank size, only the radius and number of modules per tank so as to allow high volume production methods to be employed. According to the size of tank, different sizes of angle irons can be used. For example, for tanks of from 22,500 litres to 67,500 litres the angle iron is 40 mm x 80 mm x 3 mm, whereas for tanks over 67,500 litres the angle iron is 40 mm x 100 mm x 5 mm. The apertures 12 in flanges 10 of the vertical angle irons 9 and apertures 17 In flanges 15 of horizontal angle irons 13, if required, are 8 mm in diameter and 150 mm apart.

In order to construct the tank 5, the first horizontal row of modules 6 is arranged in a circle in the desired location for the tank so that the modules are standing vertically with the radial flanges 10 of adjacent modules 6 adjacent each other. As best shown in Figure 7, bolts 22 are then passed through apertures 12 of adjacent radial flanges 10 and clamped together by tightening a nut 23 on bolt 22. A bead of silicone can be placed along the angle irons 9 so as to form a water tight seal when the bolts and nuts are tightened.

Although Figure 2 shows a tank 5 with two rows of modules 6, one on top of the other, it will be appreciated that in many cases only one such row of modules will be desired. If, however, two or more rows of modules are necessary, the two rows are bolted together, as shown in Figure 6, using similar bolts 22 and nuts 23 passing through apertures 17 in flanges 15 of the horizontal angle irons 13. Thus, the wall of the tank is completed.

In order to construct the floor of the tank a first plastic extrusion 24 is mounted to flange 15 of the lowermost horizontal angle iron 13. As shown in Figure 5, a length of flat bar is spot welded to flange 15 to provide a step 26 upstanding from the flange 15. This can, of course, be done conveniently before the frame of the module is galvanised. The extrusion 25 comprises a lower portion 27 which fits below lower flange 15 and a clip portion 28 which extends downwardly towards the end of lower portion 27 so as to form a slot 29 in the extrusion 25. In order to mount extrusion 25 onto lower flange 15, the slot 29 is filled with silicon 30, the lower part 27 is fitted over lower flange 15 and the upper part of extrusion 25 is forced towards flange 16 until clip portion 28 clips over step 26 to create a watertight seal.

The upper portion of extrusion 25 is formed in the shape of a channel 31 having walls 32, each having a downwardly facing step abutment 33.

In an alternate embodiment shown in Figure 5A, the extrusion can comprise only the channel portion 31 with the vertical walls 32 and downwardly facing step abutments 33. This extrusion can be fastened through the bottom of channel 31 to flange 15 using rivets 34. As best shown in Figure 8, with either of the extrusions shown in Figure 5 or Figure 5A, the channel 31 forms a female half of a clamp which clamps a sheet 35 of 0.5mm food grade polymer sheeting 1n position. The sheet 35 is first cut to the approximate shape of the bottom of the tank and the outer periphery of the sheet 35 is then positioned over the handle 31 in extrusion 25. The male part of the clamp formed by extrusion 36 having ledges 37 on its lower portion which fit below step abutments 33 to clamp sheet 35 therebetween. Thus the bottom of the tank can be easily fitted on site.

The top of the tank 5 is shown in Figure 2 as being a substantially conical top 38, the configuration most preferred by consumers, especially those that live in areas that experience significant precipitation in the form of snow. The construction of this top is shown generally in Figures 9, 10 and 11. Although the top is conical in shape, the top supporting structure 1s all in tension rather like a suspension bridge as opposed to compression which is the normal style of manufacture.

In a compression top, all of the steel used has to have enough strength to span the tank radius in its own right and then support the top sheeting which is the actual cone seen from the outside of the tank.

This sheeting is screwed or bolted Into place through the steel beams underneath. This method produces a good job but is costly in manufacture both in labour and materials and freight costs are significantly increased because of the weight and bulk involved. A lot of extra lifting is also involved for any person involved in the transportation or installation of the tank.

In the present invention, there is provided a short centre pole 39 the length of which is ten degrees above and ten degrees below the top of the walls of the tank 5. A 10 mm flat plate 40A of suitable diameter (depending on the size of the tank) is fitted to the top end of the pole 39 and a similar plate 40B is fitted to the bottom end of the pole, whose ends are threaded to accept back nuts 41 each side of each plate 40A and 40B. The starting position for each plate 40A and 40B is 200 mm from the end of the pole 39. Radial rods 42 of 12 mm galvanised steel are fastened between the bottom plate 40B and the flange 16 of the topmost horizontal angle iron 13 at the top of the tank 5. The ends of the rods 42 are, in one embodiment, flattened and provided with an aperture therethrough so that they can be bolted using nuts and bolts 44 to the bottom plate 40B. The other end of each rod 42 is provided with a threaded portion 45. The flange 16 is provided with apertures 43 at appropriate positions to receive the rods 42 therethrough.

Where the radial rods 42 pass through the apertures 43 1n the flange 16 at the top of the tank 5, lengths of 1.2 mm x 32 mm galvanised steel strapping 47 with 12 mm holes in the end of them are placed over the end of each radial rod 42 and then a nut 46 is screwed onto the threaded portion 45 of the end of the rods 42. This effectively anchors each strap 47 to the angle Iron 13.

The other end of the straps 47 are now taken to the top plate 40A at the centre of the tank 5 and secured to the plate 40A with bolts 48, although screws, such as 2 x M10 screws could alternatively be used.

In order that this lightweight steel has enough strength to support the top sheeting it has to be tensioned. To do this, firstly the back nuts 41 on the centre pole 39 are wound out towards the end of the pole at both ends, this operation will do almost all of the tensioning. If any individual rods 42 remain loose they can be tensioned by using the nut 46 on the end of each rod 42. In the case of the top straps 47, they can be further tensioned by screwing an M12 x 100 mm screw 49 that passes

through the flange 16 of the topmost angle iron 13 from the inside of th tank 5 directly above the radial rod 42 so as to engage the strap 47.

This tensions the strap 47 by pushing against it as it passes over the screw 49. At the conclusion of this operation, a light steel superstructure is now in place which tensions the structure of the tank and provides a secure support fot the conical top.

As best shown in Figure 10, the galvanised straps 47 running to th top plate 40A, form the two long sides of a triangle. Galvanised steel sheeting 50 is cut to the shape and size of this triangle with 16 mm extra on each long side. This 16 mm is then bent right over and flattened down to the thickness of the galvanised strapping as shown in

Figure 11.

These triangles 50 of galvanised steel can then be fitted to the steel strapping 47 simply by holding half of them (one at a time) underneath the steel strapping with their top-most end up against the centreplate. This will allow the 16 mm that has been bent over on the sheeting to clear the strap support 47.

By keeping the sheeting hard up against the strap 47 for Its entir length, it can now be slid downwards towards the tank wall. The 16 mm return on the sheet 50 will now pass over the top of the strap 47. When

1t reaches the centre of the strap 47, the sheet 50 will be at the botto of its stroke and locked into position.

When every second panel 50 has been fitted from inside the tank 5, the remaining panels 50 can be fitted in like manner, but, reversed from outside. The last operation 1s to fit a top cap 51 to the tank 5, this covers the very top centre of the tank 5 above where the sheets extend to. The cap 51 is fitted with a self drilling screw that passes through the cap edge, a top panel, the support strap then the underside top panel. This screw is not only to fit the top cap but also to stop the top panels moving upwards and becoming unhooked off the support strap.

Thus the entire top of the tank can be fitted with no fasteners at all except for the locking screw. This amounts to more saving in time and materials.

As an alternative to this conical top 38, there can be fitted a flat top to the tank 5. This can take the form of a flat corrugated iron top. Such a top can be made no more than 2.4m long so that they will fit across a standard truck body or container and therefore reduce freight costs. A problem arises 1n producing the curve shape to fit the round

water tank, since no tooling exists which will cut smoothly across a corrugated profile. This problem is solved by marking out patterns for each section to the shape it would be with no corrugations in it. Each section is then traced onto flat galvanised Iron, which can be cut with standard tooling to produce a smooth and burr free cut. The sections ar then put through a rollforming machine which corrugates them and in so doing returns the curved portions to a perfect radius.

The top is supported in position by one or two light and simple trusses (depending on tank diametre ⁾ of conventional design. As shown in Figure 12, the open end of the corrugated top 52 is sealed using a bitumen impregnated foam rubber strip 53 which is 38mm x 25 mm in cross section. The strip 53 1s placed between the corrugated iron top 52 and the top flange 15 of horizontal angle iron 13 of the tank 5. When screwed down using conventional roofing screws 54 the strip 53 compresses forming a seal that will exclude even fine dust.

Thus, the present invention overcomes a number of problems. The first one, that of avoiding materials that would pollute the water, was overcome bu using the B.H.P product 'AQUAPLATE'. Another of the significant problems was to produce a tank that lent itself to speed in production but retained ease of assembly by unskilled labour and still remained environmentally unobtrusive to the eye in a rural scene.

A further problem was that the pitch and depth of the corrugations are notoriously inaccurate. This is not a problem in conventional tank manufacture but when the profiles are required to fit into an assembly jig and the pitches have to match holes in other components 1n that jig this inaccuracy becomes are real problem.

It is not possible to manufacture corrugated iron sheets that are always perfect in pitch and depth because the hardness of the galvanised coil feed used to rollform corrugated iron always varies slightly. The harder the coil the shallower and wider are the pitches and vice versa. This problem has been overcome by incorporating into the assembly jig a method of stretching or compressing the corrugated iron sheets to bring the pitches into line with the holes in the galvanised steel section mounted in the jig that the sheets have to be riveted to. Although a particular embodiment, with some small variations, has been described, it will be apparent that a number of other modifications or improvements can be made by a person skilled in the art without departing from the scope of the present invention.

For example, to make the erection of the tank simple and speedy fo the customer it could be made in 6 metre prefinlshed modules. There could be 8 sheets per module, each sheet covering 762 mm. After the 8 sheets are all joined and sealed, a 50 x 50 x 6 mm galvanised steel angl curved 'toe in' to the tank radius could be fitted on top of the joined sheets in the assembly jig. The angle is placed with the 'toe' of the angle facing the centre of the tank. The opposing side of the angle has 4 mm holes drilled along its 6 metre length at 76.2 mm centres.

Steel bars laying across the assembly jib parallel to the sheet corrugations are welded to the jig at 762 mm centres (the design pitch o each sheet). When the angles are clamped down tight at each end of the sheets they are stretched or compressed to their design pitch and therefore each corrugation lines up with its corresponding hole in the galvanised angle. The sheets are now riveted to the angle through these holes. The unit is now structurally complete and can be lifted off the assembly jig.

The only remaining tasks to be done are to run a 12.7 mm drill through the same sized hole already in the top angle to clear away the corrugated sheet that has been riveted over the hole. These holes are for the 12 mm radial rods previously explained. The final task is to la a bead of silicon sealant along the bottom edge of the corrugated sheets where they meet the inward facing 'toe' of the galvanised angle.

Tanks can be made with two, three, four, five and six sections in heights of 1.88, 2.1, and 2.44 metres. The various combinations will produce storage capacities from 48,000 to 260,000 litres.

An objection raised by many people in the past concerning the installation of a water tank, 1s the need for them to pour concrete, or to provide a brick and timber tank stand of suitable proportions to moun the tank on to protect it from ground movement. The present invention i intended to overcome this disadvantage.

One possibility, other than that described above, is for the botto sheet to be screwed down between the galvanised steel section, one flang of which passes under the corrugated sheeting and protrudes 25 mm clear of the sheeting Inside the tank, and a 25 mm x 5 mm flat bar curved on edge to match the curve of the galvanised section. This flat bar has holes 75 mm apart to match the holes 1n the galvanised tank flange. The screws used for this operation are stainless steel roofing screws. This

type of bottom will withstand all ground movement no matter how severe, and site preparation is minimal, requiring only a level area covered wit about 25 mm of sand.

Various other modifications and improvements will be apparent to a person skilled in the art. For example, although the specification describes circular (cylindrical ⁾ tanks, the invention is also applicable to generally circular tanks which includes elliptical, pentagonal or octagonal cross-sectional shapes.