Background of the invention When pumping water that contains considerable amounts of solids, such as soil particles and plant parts, it is often necessary to provide the inlet to the pumping system with some kind of filter to prevent pumps, nozzles and pipes from being clogged. This is necessary irrespective of the purpose of the pumping, which, in some cases, actually is to separate and utilize the solids from the water by means of said filter, whereas in some other cases one only wants to transport water from one place to another, the solids mainly being considered as an obstacle for the operation of the pumping system.

Such a filter may, for example, take the form of a coarse-meshed net that captures solids. These solids have to be cleaned away from the filter to ensure that it continues to operate. This cleaning may be a time-consuming and work- demanding operation, especially if the filter is positioned in an inaccessible place, such as down in a well hole. Consequently, there exists a need for the cleaning to be as simple as possible to accomplish, and that it preferably requires as small amount of manual effort as possible.

One approach to solve the problem of cleaning filters is to reverse the direction of flow, thereby flushing captured substances away. Known systems using flow in a direction opposite the working direction are, for example, shown in DE 2442345 and WO 91/02578. A disadvantage with such a system is that it has to include means for producing said flow in the opposite direction.

The purpose of the present invention is to provide a filter device for the separation of solids from a liquid or a gas, which is easy to clean and operate.

Providing a filter device comprising the characteristics claimed in claim 1 has solved this purpose. Further, preferred embodiments of the invention may include one or more of the features claimed in the dependent claims.

Short description of the drawings Figure 1 shows schematically, from the side, one embodiment of the invention according to Example 1, in rest position.

Figure 2 shows schematically, from below, one embodiment of the invention according to Example 1, in rest position.

Figure 3 shows schematically, from the side, one embodiment of the invention according to Example 1, in working position.

Figure 4 shows schematically, from the side, one embodiment of the invention according to Example 3. For the sake of clarity only the ring attachment is shown in detail.

Figure 5 shows schematically, from below, the ring attachment according to Example 3.

Detailed description of the invention In Figure 1 to 5 a preferred filter device according to the invention is shown, comprising a hollow cylindrical body 1, the wall of which in its lower portion is in the form of ribbons 2, which extend in the extension of the cylindrical body and being arranged in a spiral so as to overlap each other and forming a funneled shape, the ribbons being kept in place by a movable tightening 3, and the cylindrical body being rotatable, by a suction force provided in the axial direction at an outlet 4 in the upper end of the cylindrical body, by means of the turbine effect that arises when water flows in through an inlet 5 in the lower end of the cylindrical body and passes the overlapping ribbons, and the overlap of the ribbons being movable between at least two positions.

It should be noted that the overlapping ribbons 2 not necessarily are completely sealed against each other. Therefore, when said suction force is applied, water can flow into the cylindrical body 1 through the spaces existing between these ribbons 2. Consequently, said inlet 5 comprises the hole shown from below in Figure 2 and/or the spaces between the overlapping ribbons.

The principal matter of the invention is therefore the turbine effect and the flexibility of the overlap, i. e. the design with ribbons being movable between at least two positions in accordance with the present pressure conditions. This design provides the specific advantages of the invention.

The invention is based on the principle that water is pumped in the axial direction through a hollow cylindrical body, which is caused to rotate around its

axis by the flow depending on the cylindrical body having the form of ribbons that partly overlap each other and form a turbine-like structure. During operation, the flow inside the cylindrical body may be described as a vortex directed upwards, the overlapping ribbons acting as a kind of turbine. Solid substances then have a relatively long transport distance consisting of several turns through the cylindrical body, during the corresponding time of which they have the opportunity to fasten in the grooves created by the overlapping ribbons.

The surprising effect provided by the invention is that it utilizes the fact that the ribbons are in different states of overlap when different pressure conditions prevail in the cylindrical body. More specifically, the inner volume is smaller when a suction pressure is applied by connecting the outlet of the filter device to a pump.

When the pump is disconnected, the flow of water and the rotation of the cylindrical body stop, and, simultaneously, the inner volume increases as the ribbons move outwards and sidewards in relation to each other. Solid substances, which have been captured in the grooves, are then released because, among others, the ribbons suddenly move sidewards thereby displacing the walls of the ribbons, the ribbons move outwards, and the flow through the cylindrical body is disrupted.

The solid substances are caused to fall down by the force of gravity, after they have been released from the ribbons, and, since the cylindrical body preferably being arranged vertically, they fall out from the inlet of the filter device, whereupon they may or may not be utilized as desired. In the present description, the expressions "upper"and"lower"parts and ends etc. with respect to the cylindrical body, are used to denote preferred positions, when practicing the invention, when one wants to allow solid substances sediment by themselves in the rest position. The rotation and other operations of the filter device work, however, independent of the position, which is obvious for a person skilled in the art.

In principle, it is conceivable that a funnel-liked or cylindrical construction, having a non-flexible inner turbine structure, would provide a desired filter effect.

However, the remarkable advantages of the invention appear only if the construction having two mutually movable ribbons is used by means of the movement of the ribbons between two position being relatively sudden when a connected pump is turned-of£ Then the cleaning takes place with a considerable efficiency, which is substantially higher than it would be if no such movement between two positions would occur.

Further, in the present system no flow in the opposite direction is utilized, but only a discontinuation of the flow, which, in many cases, is advantageous since no means have to be installed in order to produce flow in the opposite direction, compared to the working direction. Neither are any mechanical means needed being especially intended for the cleaning.

In practice, one may utilize the invention in such a way that, in order to clean a filter device according to the invention, the pump is simply turned-off. The cylindrical body will then stop within a few seconds, and any substances captured will fall out from the filter device and down to the bottom. Thereafter, the pump can be turned-on again. The time period during which the pump is turned-off may be very short, for example less than 10 seconds, and should be adjusted in relation to the solid substances, so that all of the captured substances have time enough to sediment out from the filter device.

For some applications it may be appropriate to provide the pumping system with a time controller, for example a timer, so that the pump is turned-off at certain times, whereby the filter device is"cleaning itself.

Below the different components of the invention according to the invention will be discussed in more detail.

The most important feature of the cylindrical body is that it is rotational symmetric and hollow, so that a flow can take place through the cylindrical body during rotation. In the embodiment shown, the body has a drop like shape, narrowing upward, but the narrowing is not critical. However, it may be advantageous that the surface lying against the upper connection in rotation (in working position) neither is too large, which involves large friction, nor too small, which could lead to an oscillation of the cylindrical body that is difficult to control.

The cylindrical body may be provided with a flange, which, in rest position, rests on the suspension collar of the connection (see below).

The ribbons should have a size that fits the intended use. The rotation, the filtering and the cleaning are dependent on the design, arrangement and material of the ribbons. The portion of the ribbons being below the tightening acts as a propeller that counteracts the main rotation of the cylindrical body and increases the turbulence around the inlet. In working position, i. e. rotating state, the volume of the cylindrical body is influenced by, among others, the characteristics of the material, the suction force, and the centrifugal force arising when the cylindrical

body rotates. Therefore, the suction force will be balanced by the centrifugal force, the inner volume in general being smaller in working position than in rest position.

The tightening may be a ring of a stable material, for example hard plastic, and provides the function of maintaining the main position for the ribbons. The ring may be mounted around the ribbons in such a way that an inlet with suitable size is provided.

In its upper end, the filter device is preferably provided with a connection attachment 6, which has a surface against which the outlet end of the cylindrical body can rotate, and a suspension collar 7 to keep the cylindrical body in place close to the pump hose in the rest position (see Figures 1 and 3). The cylindrical body should be held so close to the suction hose that it is sufficiently to turn-on the pump to allow the cylindrical body to be sucked into position in the working position.

Advantageously, in some applications, the hollow cylindrical body may be supplemented with an outer attachment 8, having wings 9 directed outwards and upwards and acting as a propeller that follows the rotation of the cylindrical body and creating a flow of water upwards, along the cylindrical body. This may be suitably in order to prevent, for example, elongated green algae from sticking on and winding around the cylindrical body. This function is accomplished partly by the flow directed upwards, partly by the wings cutting tender substances, such as green algae, into pieces.

The applicability of the invention The present invention can be applied for many different purposes, as is obvious for a person skilled in the art. The pumping of water containing sludge in abundance can, as an example, be mentioned.

The invention is particularly useful when one, at a minimum of maintenance and at low costs, wants to secure the operation of pumping systems. This may for instance apply to pumping of water between ponds in a garden. One may also consider a lowering pump in a well, where it is an advantage to not be obliged to bring the filter up from the water, or send a person down to carry out the maintenance.

In such applications, one is not at all interested in taking care of the captured substances. However, it is equally possible to implement collecting means, which takes care of the substances as they fall out from the filter device when the pump being in the off-position.

Herein the present invention has mainly been described in connection to pumping of water. However, there are no features which are unique for water that have been used, the filter according to the invention will, therefore, work as well for other liquids. As is apparent from Example 4 below, the same principle work also for gases, and the invention includes therefore also filter devices in fan systems for gases.

Below the invention is illustrated by means of exemplifying embodiments.

Example 1 A filter device was made based on a standard 50 cl bottle, made of a so called PET-bottle having a height of approximately 23 cm and a diameter of approximately 6 cm at the non-conical part, which was cut so that the bottom was removed and the non-conical part was cut to the shape of longitudinal ribbons, about 12 cm long, about 5 mm wide and about 0.5 mm thick. The ribbons were arranged in a helical form, so that they overlapped each other and were held together by a rubber band, if necessary supplemented by a ring of PET-plastic. The tightening was situated approximately 3 cm above the lower end, and there the opening was approximately 2 mm in diameter in the rest position. The upper part of the filter device consisted of a removable connection attachment consisting of the neck of a similar bottle and about 2 cm of the conical portion of this bottle, the lower part of which was provided with a non-sealing inner collar, which holds the outlet end of the cylindrical body in place inside the connection attachment.

This filter device was connected to a pumping system for garden ponds (pump of the type Utfors with a capacity of 30 minute-liter) and was completely immersed in a garden pond in Alunda, Uppland, during summer time. The pumping was done with an effect of 900 W during 4 months, whereby the cylindrical body was rotating with approximately 200 revolutions per minute. The filter device was cleaned by turning-off the pump once a day. Generally, there was no need for further cleaning, and the pumping was regarded as completely satisfactory. During periods with an abundance of green algae, which had a length up to half a meter, these algae had, however, a tendency to stick to and wrap around the cylindrical body of the bottle, wherefore the measure described in Example 3 was taken.

Example 2 A device similar to the one described in Example 1 was made with the same dimensions, except that this time the walls of the cylindrical body of the bottle were about twice as thick and, therefore, less flexible. The filter device was tested in a similar way as the filter device in Example 1, but not for as long time. One could observe that the difference in inner volume and overlap between working position and rest position was not as large as with the filter device according to Example 1.

The filtering was regarded as being satisfactory also in this case.

Example 3 An attachment, consisting of a ring provided with wings directed outwards and upwards, replaced the tightening ring in the filter device according to Example 2. Comparisons were made with the same filter device in operation without the attachment ring, whereby the attachment ring resulted in a decreased tendency for gathering of long green algae around the cylindrical body.

Example 4 An ordinary domestic vacuum cleaner (Electrolux Excellio Z5040) was connected to each of the filter devices according to Example 1 and 2. They both rotated, except at the lowest effect, with approximately up to 300 revolutions per minute, whereby the inner volume was smaller in the rotational state than in the rest position. This example shows that the principles of the invention also work for gases.