The invention relates to a tank according to the preamble of claim 1.
Tanks, such as sewage holding tanks, usually have a cylindrical or spherical form. The prior art also shows a sewage holding tank in the shape of a ball with spherical indentations removed from opposite sides thereof. It is rather difficult to provide a cylindrical sewage holding tank with sufficient strength properties. On the other hand, it is difficult to transport spherical sewage holding tanks, which require for example separate legs or some other corresponding supports during the transportation in order not to fall over. Further, a problem that is common to all sewage holding tanks is that their depth of installation is rather great, i.e. installation of the tanks requires the excavation of quite a deep pit. Also, it is rather difficult to anchor especially plastic sewage holding tanks in place so that they will not be moved by soil frost or ground water.
US-A-5 628 420 discloses a rollable container. The container comprises a hollow enclosed substantially cylindrical rigid body. The body is provided with an elongate passageway extending through the body along the cylindrical axis thereof. The container is provided with a handling device for retaining the container rotatably about the cylindrical axis.
US-A-4 475 662 discloses a toroidal pressure vessel of compound material. The pressure vessel has an inner core, which is very lightweight and made of rubber for example. The core has an inner toroidal shape and an outer cylindrical contour. A first plurality of filament windings is wrapped in a meridian direction around the core and an additional plurality of filament windings is wrapped equatorially on the vessel around the cylindrical contour.
The purpose of the present invention is to provide a tank where at least some of the aforementioned disadvantages can be avoided.
The tank according to the invention is characterized by the characterizing part of claim 1.
The basic idea of the invention is that the inner surface of the tank is substantially torus-shaped. The idea of a preferred embodiment is that also the outer surface of the tank is substantially torus-shaped. The idea of another preferred embodiment is that the surface of the tank is provided with ribs that reinforce the tank structure. The idea of a third preferred embodiment is that the ribs provided on the surface of the tank are made such that grooves are formed on the outer surface of the tank. The idea of a fourth preferred embodiment is that the tank is provided with at least one preformed opening in order that a separate pipe fitting can be arranged to be used as an inlet/outlet fitting or as a rising pipe. The idea of a fifth preferred embodiment is that the tank is converted into a septic tank through the installation of partitions inside the torus-shaped tank.
An advantage of the invention is that when the tank is laid in the ground, it does not require a very deep pit. For example, the tank of the invention does not require as deep a pit as is required for the same volume in a spherical or cylindrical shape. Further, the structure of the tank is rather strong and it can be made such that it does not contain long horizontal surfaces but, for example, mainly curved surfaces. Due to the curved surfaces the loads stressing the structure are distributed advantageously with respect to the strength properties. Further, the tank can be anchored to the ground rather easily if the outer surface of the tank is also torus-shaped, since the anchoring can be implemented utilizing a hole that is situated in the middle of the tank outside it. Also, during the transportation the tank remains in an upright position without the need to use separate legs or other special arrangements to support the tank. By means of the ribs the structure can be strengthened further. When the ribs are positioned such that grooves are formed outside the tank, the grooves can be utilized as guides for ropes that anchor the tank in place. When a separate pipe fitting is used as an inlet/outlet fitting or as a rising pipe, a pipe can be installed and fastened from any direction of the tank. installation of partitions in the torus-shaped tank provides a compact septic tank in a simple and easy manner.
The invention will be described in greater detail in the accompanying drawings, in which
Figure 1 shows a tank 1, which is made of a plastic material, for example a polyolefin, such as polyethylene PE, polypropylene PP or crosslinked polyethylene PEX. The tank 1 shown in the figure can be formed as a single piece for example through rotational casting. The tank 1 can be used as a fluid tank for storing for example water or, for example, a sewage holding tank for storing waste water or some other waste liquid. Further, the tank can also be used as a septic tank or a part thereof. The tank is thus pressureless and intended to be used buried in the ground. The inner surface of the tank 1 is substantially torus-shaped so that the height of the tank is smaller than the height of a spherical tank for the same volume. The definition "substantially torus-shaped" means that the inner surface of the tank 1 has a similar shape as a surface formed by a closed curve which has revolved around the axis on the same level. Further, the definition "substantially torus-shaped" means that the closed curve can be for example circular but it can also be oval and it may comprise straight sections in the upper and lower parts thereof and on each side, and the curve may even be rectangular, as shown in greater detail in Figures 2 and 3, and 9 to 12. In the embodiment shown in Figure 1, the outer surface of the tank 1 is also substantially torus-shaped, and there is a hole 2 situated outside the container of the tank 1 intended for storing liquid, the hole being also positioned in the middle of the tank 1. Therefore the walls of the tank 1 do not comprise long unsupported horizontal sections and the walls can be made rather thin.
The walls of the tank 1 can be provided with ribs 3 that support the walls. The ribs 3 are preferably formed such that the wall of the tank 1 is shaped so that it is provided with grooves which are directed inwards. The grooves formed by the ribs 3, and the hole 2 of the tank 1 can be utilized when the tank 1 is being anchored in place. The number and shape of the ribs 3 may vary according to the needs. The tank 1 can be laid in the ground, but if desired, it can also be installed indoors. Despite the rather great volume of the tank 1 the tank is not very high, wherefore it does not require a very deep pit in order to be installed. For the sake of clarity, the ribs 3 are not shown in Figures 2 and 3.
The tank 1 is provided with three preformed openings 4, at least one of which is opened when the tank 1 is taken into use. There must be at least one preformed opening 4 and the number thereof may vary depending on the size and intended use of the tank 1. A separate inlet or outlet fitting or a rising pipe is to be connected to the opened preformed opening 4. Instead of a preformed opening 4 and a separate fitting, the tank 1 can also be provided with a desired number of fixed fittings. The upper part of the tank 1 is also provided with anchor fasteners 5, which can be used to anchor the tank 1 in place. The anchor fasteners 5 can also be utilized as lifting lugs so that the tank 1 can be fastened easily to a lifting apparatus.
The tank 1 is shown in Figure 4 in a top view and in Figure 5 in a bottom view. Figure 5 shows recesses 6 formed in the ribs 3 and placed at the bottom of the tank 1 to ensure that a segment between two ribs 3 will not contain any liquid after the tank 1 has been emptied.
Figure 6 shows an arrangement where the tank 1 is converted by means of partitions 7 into a septic tank with three chambers. The septic tank comprises separate chambers through which waste water flows. Water is arranged to flow as slowly as possible from the upper part of a preceding chamber to the next chamber in order that the greatest particles in each chamber have time to fall to the bottom of the chamber to form precipitate. When the waste water has passed through the last chamber, all the solids that might interfere with the subsequent cleaning have been separated from the water. With two partitions 7 it is possible to provide a two-chamber septic tank. As shown in Figure 6, the volume of the first chamber is most preferably about half of the total volume of the tank 1. A preformed opening 4 provided in connection with each chamber is opened and a rising pipe is placed in the opened preformed opening for the purpose of emptying the chamber. The first chamber can be provided, for example, with a fitting 8 shown in Figure 7, the horizontal part 8a of the fitting 8 forming the inlet fitting and the vertical part 8b forming the rising pipe intended for emptying. In the direction of flow of waste liquid, i.e. between the first and the second chamber, and correspondingly between the second and the third chamber, the upper part of the partition 7 comprises one or several holes via which the waste liquid is able to flow to the next chamber. The last chamber in the direction of flow of the waste liquid is provided with an outlet fitting directed sideways, as shown for example in Figure 2 by a broken line.
Figure 7 shows a separate fitting 8, which is placed in connection with the opened preformed opening 4, and which may be an inlet fitting or an outlet fitting or a rising pipe used for emptying. The fitting 8 is sealed to the tank 1 by seals 9. The use of a separate fitting 8 enables, for example, the fastening of an inlet pipe to the tank 1 from any direction. Therefore, when the tank 1 is being laid in the ground, the direction of the inlet pipe does not have to be known exactly and the position of the tank 1 can thus be selected rather freely during the installation. The diameter of the preformed opening 4 and the fitting 8 can vary depending on the needs.
Figure 8 shows a tank 1 comprising one partition 7. The tank 1 also comprises an inlet fitting 10 and an outlet fitting 11. The partition 7 most preferably extends continuously from the bottom to the top. Therefore the liquid flowing into the tank 1 enters through the inlet fitting 10 and is discharged through the outlet fitting 11, and it flows in the tank 1 in the manner shown by arrow A and it settles in the tank 1. Therefore the tank 1 operates as a settlement tank in the embodiment shown in Figure 8.
Figure 9 shows a tank 1 the outer surface of which resembles a flattened sphere. However, since the inner surface of the tank 1 is substantially torus-shaped, the tank 1 comprises in the middle a supporting section, wherefore the tank 1 does not comprise long horizontal unsupported parts. For example compared to the arrangement shown in Figure 3, the solution of Figure 9 does not comprise a hole 2 situated in the middle of the tank outside it, but the hole is replaced in the tank of Figure 9 with the supporting section. The tank 1 of Figure 9 can be made, for example, by manufacturing through injection molding two tank halves that are joined.
Figure 11 shows a tank where the outer and inner surfaces are substantially torus-shaped, and the torus surfaces are formed by circles that have revolved around the axis on the same level. The torus surfaces of the tank shown in Figure 10 are formed by ovals which have revolved around the axis on the same level. Also in the arrangement of Figure 3 the torus surfaces are formed by ovals, but therein the area of the horizontal surface is smaller than the area of the vertical surface, whereas in Figure 10 the area of the horizontal surface is, in turn, greater than the area of the vertical surface. In Figure 12, the torus surfaces of the tank are formed by rectangles which have revolved around the axis on the same level. If desired, the rectangles may have rounded comers.
Figure 13 shows a tank 1, which is provided with a rising pipe 12 substantially in the middle of the tank 1. The diameter of the rising pipe 12 is greater than the diameter of a hole 2 or, for example, the diameter of the supporting section of the tank shown in Figure 9. Further, on the section inside the rising pipe 12 the tank 1 comprises openings 13, so that the interior of the tank 1 is connected to the rising pipe 12. Also, if there is a hole 2 in the middle of the tank 1, the hole 2 is provided with a bottom 14. Further, it is possible to provide one or more openings in the tank 1, for example in the lower part thereof, as shown with a broken line in Figure 13.
Figure 14 shows a detail of a wall of a tank, the wall consisting of several layers. The innermost layer 15a is preferably lighter than the other layers. This facilitates checking and maintenance of the tank. For example, less light is needed inside the tank during maintenance and checking when the innermost layer 15a is light compared to a situation where the innermost layer 15a is dark. Further, when the wall comprises more than one layer, one of the layers can be made of closed cell polyolefin. Closed cell polyolefin acts as heat insulation, providing thus a thermally insulated tank. For example in the embodiment of Figure 14, the middle layer 15b is preferably made of closed cell polyolefin, whereas the innermost layer 15a and the outermost layer 15c are made of normal polyolefin.
The drawings and the related description are only intended to illustrate the inventive idea. The details of the invention may vary within the scope of the claims. Therefore the tank 1 can be provided with a spirit level with which the horizontal position of the tank 1 can be checked easily during the installation. The tank 1 is typically mounted in a horizontal position as accurately as possible in order to prevent for example the formation of air pockets in the tank 1. Naturally, the tank 1 can also be installed in some other position than horizontally. Further, the tank 1 can be provided with an alarm, which identifies the boundary between air and water and indicates that the tank is full. The alarm indicating the filling of the tank is most preferably installed in a rising pipe so that it can be easily replaced and handled in connection with breakage and/or maintenance.