Storage tank

Abstract

 A tank for storing a large quantity of liquid, e.g. drinking water or sewage is formed from a flexible light-weight bag (5) located within a wire mesh surround (1). The bag has vertical rigid or semi-rigid ribs (6) fixed to its side walls. As liquid is emptied from the tank the sides of the bag collapse inwardly and are raised again when the bag is filled. The ribs prevent the back from crumpling and prevent folds of material being trapped when the bag is refilled.

Description

[0001] This invention relates to storage tanks and particularly to tanks for storing large quantities of liquid such as swimming pools, reservoirs of drinking water, fish rearing tanks etc.

[0002] There are many occasions when it is desirable to construct a large water storage enclosure from flexible, light-weight material such as PVC-coated polyester cloth. For example, a drinking water reservoir to be constructed in a remote location requires materials that are easily transported. It is however desirable that the flexible material should be able to collapse inwardly when the tank is empty, otherwise it will be vulnerable to wind damage. Furthermore the flexible material should fold inwardly without such crumpling or creasing that causes folds of material to be trapped when the tank is refilled.

[0003] According to the present invention there is provided a storage tank for large quantities of liquid comprising a bag of impermeable, flexible material having a side wall or walls enabled to collapse inwardly and be raised outwardly when the tank is emptied and filled respectively, the collapsible walls of the bag having a plurality of spaced rigid or semi-rigid ribs fastened thereto and thereby acting to prevent trapped folds in the bag as the tank is filled.

[0004] An embodiment of the invention will now be described by way of example only, with reference to the accompanying drawings. In the drawings:-

Figure 1 is a plan view of a circular tank in accordance with the present invention;

Figure 2 is a side elevational view of the tank with part of the wall shown cut away;

Figure 3 is a schematic illustration of a tank, partially full of liquid.

Figure 4 is a plan view of an alternative fabric sleeve opening to the tank; and

Figure 5 is a view in elevation and partial cross-section on the line X-X of Figure 3.

[0005] Referring to the figures, the construction of a water storage tank is begun with the assembly of a circular steel wire surrounding wall 1. This steel wire is preferably of the galvanised, welded form sold under the trade mark "Weldmesh" which can be transported in rolls typically 3 feet wide and 3 feet in diameter. The circular wall 1 formed from the wire mesh is located and fixed by means of a number of wooden posts 2 which are driven into the ground adjacent the outer surface of the wire mesh wall 1, the wire mesh being stapled to the posts. Where the ground is uneven, the top edge of the wall 1 is levelled by sinking the bottom edge into small trenches where necessary e.g. the trench 3. The wall 1 is completed when two ends of wire mesh from the roll are joined together. This is accomplished with the use of two joining bars 4 which are disposed vertically with respect to the wall 1. The two joining bars 4 face one another on opposite sides of the overlapping ends of the wire and are bolted together through the wire mesh. Since hoop tensions are greatest at the bottom of the tank and are zero at the liquid surface, the spacing of the bolts needs to be closer at the bottom than it does towards the top of the tank.

[0006] A large, closed cylindrical lining bag 5 is positioned within the circular wire mesh wall 1. The liner is made from flexible material such as PVC-coated polyester cloth, hypalon-coated nylon cloth or other similar material which is chosen to suit the type of liquid that the container is intended to hold. The liner 5 is secured to the post 2 at ground level but is not connected to the wire mesh wall 1 so that when the tank is empty it will tend to collapse inwardly.

[0007] A number of lengths of polythene piping 6 or other rigid or semi-rigid members are fastened to the side of the lining material 5 and when the tank is full these pipes 6 are upright. The pipes 6 may be connected to the flexible material along their lengths, or alternatively a number of pockets 5a may be formed in the lining into respective ones of which the pipes can be inserted. When the tank is emptied, the sides of the liner 5 still collapse inwardly but do not crumple since they are kept extended by the pipes 6. The polythene pipes 6 bend inwardly under the unsupported weight of the exposed lining walls as the tank is emptied. The lining is thus peeled away from the wall 1. When the tank is refilled the lining unrolls against the wall and the pipes 6 straighten so that creases do not form and therefore folds of lining material do not get trapped by the introduced liquid.

[0008] Figure 3 illustrates the manner in which the pipes 6 bend and support the side wall of the lining When the tank is partially full This illustration shows an open-topped version of the tank.

[0009] The outlet for liquid from the tank is provided in the bottom surface of the flexible liner by an outlet orifice cut from the bottom of the liner. A flange 7 is located over the orifice on the inside of the tank and this is in register with a flange 8 which is located beneath the lower surface of the tank opposite the flange 7. The flanges are then screwed or bolted together with lining material surrounding the orifice being held between them. The lower flange 8 has permanently connected to it an elbow pipe fitting 9 situated beneath ground level. A flexible suction hose 10 is connected to the fitting 9 and extends out from under the edge of the tank. The material of the hose 10 is chosen to be compatible with the liquid stored in the tank. A wooden post 11 stands up next to the tank and supports the upright portion of the hose 10. The upright portion of the hose 10 may be connected to the post 11 by a short chain 12 at its upper end. The hose thus secured has its open end above the level of liquid in a tank and the pipe may then be used for filling or emptying if the chain 12 is unlocked. This arrangement avoids the need for a stop valve but in an alternative version the post 11 is replaced by a stop valve. In another alternative version, the hose is connected to a more elaborate pipe system. However, in the embodiment described above, a simple system is provided which can be installed by unskilled persons.

[0010] In the closed tank shown in Figures 1 and 2 the top surface of the flexible liner has an opening 13 which is directly above the orifice enabling the internal flange 7 to be readily located. The opening 13 has connected around it a fabric sleeve 14 which is closed by clamping bars.

[0011] Referring to Figures 3 and 4, in a modified version of the sleeve opening a polystyrene cylinder 20 having an outside diameter to permit it to slide as a close fit into the sleeve 14 is used as a plug and secured by a clamping band 21 around the sleeve. The cylinder 20 is arranged to project down below the lower end of the sleeve so that the lid or cover of the tank is slightly raised at this place to encourage air to move to this spot. The polystyrene cylinder 20 has a central axial bore 22 through it, which intersects several radial bores 23 made at the level of the lid or cover of the tank, thus allowing trapped air to vent freely to atmosphere. A simple mushroom type cover 24 may be fixed on top of the plug to stop rain water or pollutants entering the vent.

[0012] The fabric sleeve could in an alternative version be replaced by a rigid inspection cover but whatever arrangement is used, it should permit ventilation of gas or air particularly when the tank is being filled.

[0013] A storage tank in accordance with the invention may be constructed with rigid ribs 6, for example, wooden battens, in place of the polythene tubes in the example described above. Such rigid members do not bend and peel away from the support wall when the tank is emptied but tilt inwardly. It has been found that in most applications the semi-rigid bendable ribs are preferable.

Claims

1. A storage tank for large quantities of liquid comprising a bag of impermeable, flexible material having a side wall or walls enabled to collapse inwardly and be raised outwardly when the tank is emptied and filled respectively, the collapsible walls of the bag having a plurality of spaced rigid or semi-rigid ribs fastened thereto and thereby acting to prevent trapped folds in the bag as the tank is filled.

2. A storage tank as claimed in claim 1 characterised in that the ribs are resiliently deformable to the extent that the ribs bend inwardly under the weight of unsupported bag material when the tank is emptied without folding or crumping.

3. A storage tank as claimed in claim 2 characterised in that the ribs comprise polythene tubes.

4. A storage tank as claimed in any one of claims 1 to 3 characterised in that the ribs comprise separate members and the bag includes a plurality of pockets in which the members are situated to fasten them to the bag.

5. A storage tank as claimed in any one of claims 1 to 4 characterised by the inclusion of a substantially rigid outer supporting wall or walls.

6. A storage tank as claimed in claim 5 characterised in that the outer supporting wall comprises wire mesh.

7. A storage tank as claimed in claim 6 characterised in that the outer supporting wall is formed from a single length of material whose free ends are overlapped and clamped between upright clamping bars.

8. A storage tank as claimed in any one of the preceding claims wherein the bag is a substantially closed container.

Drawing