Device and method for filtering particles from a liquid in a dishwasher

The invention relates to a device and a method for filtering particles from a liquid in a dishwasher.

Mechanical filters, for example, comprising a lattice network or a metal film with pores, have long been known for filtering particles from a liquid, especially a dishwashing fluid. The operating mode of these filter devices is substantially determined by the surface condition and the pore size of the filter. For cleaning these rigid filter devices, for example, flow reversal can be effected whereby any particles adhering in the filter device are removed and transported away from the dishwasher.

Since the size of the pores substantially influences both the filter capacity and the cleanability, in conventional dishwashers a pore size is selected which ensures the filtering of small particles and also a good cleanability. Nevertheless, despite multistage filter devices, it is not possible to filter out fine and superfine particles such as food residue, for example, from the circulating dishwashing fluid in conventional dishwashing machines. These particles are therefore continuously circulated and are only removed in part from the circulating cycle into the waste water at the end of the washing program, for example, during the clear rinsing.

It is thus the object of the present invention to provide a device and a method whereby fine and superfine particles can be filtered out from the dishwashing fluid of a dishwashing machine.

This object is achieved by the device according to the invention having the features according to claim 1 and by the method according to the invention having the features according to claim 6 . Advantageous further developments of the present invention are characterised in the dependent claims 2 to 5 .

The device according to the invention for filtering particles from a dishwashing fluid in a dishwashing machine comprises a container into which a predetermined quantity of a liquid mixed with a foam-forming substance and/or cleaning agents is introduced and the container comprises means whereby a gaseous fluid flows through the liquid mixed with a foam-forming substance and whereon liquid mixed with a foam-forming substance forms a foam layer which exhibits filter properties so that a substantial fraction of the particles is filtered out in this foam layer and remains in this foam layer.

Advantageously, the means are constructed in the bottom area of the container and comprise openings through which a fine-beaded gas, for example, atmospheric air can flow. Appropriately provided in the upper area of the container are means through which dishwashing fluid provided with particles can flow in.

The method according to the invention is used during usage of the device according to the invention. The method for filtering particles from a quantity of liquid, especially the dishwashing liquid, substantially comprises the following steps:

1. A predetermined quantity of a liquid mixed with a foam-forming substance and/or cleaning agents is introduced into a container.

2. A gaseous fluid, for example, atmospheric air, is passed through openings in the bottom area of the container.

3. As a result of the different density conditions, the gaseous fluid flows rapidly through the pre-determined quantity of liquid mixed with a foam-forming substance and/or cleaning agents and forms a foam layer. This foam layer is formed so that it floats on the surface of the pre-determined quantity of liquid in the upper area of the container.

4. The dishwashing fluid permeated with particles, especially food residue trickles through appropriate means from above onto the foam layer formed so that the particles remain in the foam layer while the liquid, i.e. the dishwashing fluid flows past the foam bubbles or therethrough and enters into the liquid-filled container substantially cleansed.

5. The substantially fine and superfine particles collect in the foam layer and are led off at the end of the method according to the invention and removed by suction by means of the discharge pump.

The level in the container is appropriately held at a height by means of valve devices or a communicating pipe so that the height of the foam layer remains substantially the same while carrying out the method according to the invention. In one variant of the method according to the invention, the thickness of the foam layer can be varied, i.e. is embodied as adjustable in height. By metering the foam-forming substance, a foam layer of different thickness can be achieved, which is matched to the respective degree of contamination of the dishwashing fluid. For example, if a very small quantity of the foam-forming substance is added to the container by means of the dosing device, a thin foam layer is formed which can only absorb a small quantity of particles. However, if a larger quantity of the foam-forming substance is added to the container, a thicker foam layer is formed whereby larger particles or a larger number of particles can be filtered out. The requirement for foam-forming substance can be determined by means of a turbidity sensor, for example, which detects the turbidity of the dishwashing solution, and thus regulates the thickness of the foam layer.

It can be appropriate if the foam is formed continuously by means of the ascending gas bubbles while carrying out the method according to the invention or at intervals. The dishwashing fluid cleansed by means of the method and device according to the invention is supplied by means of corresponding valve and pipe systems of the circulating pump and can thus result in substantial saving of the quantities of water required.

A preferred embodiment of the device according to the invention is explained in detail hereinafter with reference to a drawing.

FIG. 1 shows a cross-section through a device according to the invention. The container 1 is preferably located in the lower area of the washing container but can also be arranged in another area of the dishwasher. A liquid 2 mixed with a foam-forming substance is introduced into the container 1 and a gaseous fluid 2 , preferably atmospheric air, flows by means of a corresponding device 6 through openings 5 located in the bottom area of the container 1 . Furthermore, the dishwashing fluid permeated with cleaning agents and possibly with food residues has properties similar to those of a liquid 2 mixed with a foam-forming substance and thus can also be used for foam formation. The dishwashing fluid enriched with cleaning agents and possibly also with food residues thus forms a liquid 2 mixed with cleaning agents.

When the gaseous fluid flows through the liquid 2 mixed with a foam-forming substance or the dishwashing liquid with food residues, a foam layer is formed, this being located on the surface of the liquid mixed with a foam-forming substance or the dishwashing fluid with food residue.

The dishwashing fluid contaminated with particles, especially food residue, is transported by the circulating pump via the path A to the means 4 and rains through these means 4 , embodied as openings, onto the foam layer 3 whereby the particles located in the dishwashing solution, especially food residue, adhere to the foam bubbles and the cleaned dishwashing solution flows into the liquid mixed with foam-forming substance located therebelow.

The dishwashing solution thus cleaned is removed via the pipe system 7 , the cleaned fraction being passed back via the path C into the washing cycle of the sump and after the dishwashing fluid has been cleaned, the contaminated foam and the remainder of the liquid flows along path C to the discharge pump and is removed there.