The present invention is related to a filter unit in accordance with the preamble of claim 1.

Conventionally, water treatment and filtering occurs principally in communal large-scale water treatment plants. In sparsely-populated areas water is purified with the help of filters installed separately in the water piping of each house and passing the entire volume of consumed water. Also conventional is the use of car¬ tridge filters installed in an individual pipe dis¬ tributing purified water to a limited number of taps, as well as the use of compact cartridge filters and devices mountable on water taps to obtain clean water from a given tap. Tap-mountable filters generally operate under line pressure, whereby filtration efficiency is lowered by the fast instantaneous flow rate during use. However, some of these devices can be operated nonpressurized. Yet, the marketplace has been lacking a low-cost filter unit, which has a design compatible with the kitchen environment and suited for use in, e.g., hotel rooms or camping/hiking, with an added benefit of serving as a drinking cup. Moreover, all commercially available minia- ture filters are too expensive for water-purifying use in developing countries.

It is an object of the present invention to achieve a filter unit capable of overcoming the disadvantages of the prior-art implementations and of attaining a cost- efficient and practical design which makes it also applicable in developing countries.

The invention is characterized by what is stated in the characterizing parts of annexed claims.

The invention according to the present patent application offers a plurality of significant advantages. As the design used in the invention is based on conventional volume-production foodstuff containers such as disposable drinking cups, its look makes it most compatible for use in conjunction with tableware or in hotel rooms. The embodiment according to the invention is most useful in, e.g., hot-climate vacation resorts, where the hot and cold water supplies of hotels often contain bacteria capable of transmitting gastro-intestinal tract dis¬ orders. A single filter unit according to the invention is capable of purifying up to 10,000 cups of water. Due to its low cost and practical design, the invention is most suited for use in developing countries, too. The filtration efficiency stays constantly good, because water flow is by gravity through the filter element. Enhanced practicality is further attained through the design of the filter body part making it suitable for use as a drinking cup.

In the following, the invention will be examined in more detail by means of a preferred exemplifying embodi¬ ment with reference to the attached drawing, in which:

Figure 1 is a simplified diagram of the filter unit according to the invention in a partially sectional side view having the filter elements partially separated from each other for greater clarity;

Figure 2 is a presentation of a method for mounting the screen meshes in the filter;

Figure 3 is a partially sectional side view of a detail in the upper edge structure of the fabricated filter unit; and

Figure 4 is a top view of a detail in the filter unit edge.

With reference to Fig. 1, the filter unit according to the invention is shown placed onto a body part 1 of the filter unit. The body part 1 serves as both a filter support and a protective/drinking cup into which the filtered liquid drips. Partially to the inside of the body part 1 is inserted a filter vessel part 2 advanta- geously so that the shoulder rims of both parts 1, 2 stackably meet at point 4. Then, the bottom of the filter vessel part 2 is aligned at the dashed line in the diagram, whereby into the body part 1, between the bottom of the filter vessel part 2 and the bottom of the body part 1, a space is provided for the filtered liquid having an advantageous volume of, e.g., 0.25 1. In the exemplifying design the body part volume is advantageous¬ ly 0.5 1.

To the bottom of the filter vessel part 2 is made at least one hole 9 having a diameter of 6 mm, for example. Over the hole is adapted a dense mesh 5 or similar con¬ struct to prevent the filtering material from escaping. The diameter of the mesh openings is in the order of 0.1 mm. Over the mesh 5 is adapted the filtering material such as silver-treated activated coal. The filtering material removes bacteria, heavy metals, humus, etc. from the raw water. Over the filtering material is mounted a receiving vessel part 3, advantageously sealed with an adhesive. To the bottom of the receiving part 3 are formed a plurality of holes 10 screened with a mesh 6. The liquid to be filtered is poured into the receiving part 3, wherefrom the liquid flows by gravity via the filtering space 8 and the bottom holes 9, 10 to the drinking cup 1. In an advantageous embodiment the meshes 5, 6 are adapted spring-loaded by means of a spring 11 to the ends of the filtering space 8, in front of the holes

9, 10. The spring 11 is advantageously a compression spring suited to press the meshes 5, 6 against the end surfaces.

To the stackable shoulder rim of the receiving vessel part 3 is provided at least one hole 12 through which the vacuum tending to slow down the through-flow can be equalized in the filtering space 8. Simultaneously, the hole assures steady filtering flow rate under all con- ditions. The diameter d of the hole is advantageously approx. 1 - 2 mm, preferably 1.5 mm. Then, the number of the holes is most advantageously three. The passageway to the air is provided by the space between the vessels 2 and 3 (Fig. 3) .

To assure hygienic integrity of the filter and provide a storage protection, the filter unit is equipped with a capping cover 13, advantageously having a gripping means compatible with rim of the receiving vessel part 3.

Accordingly, the filter vessel part 2 is fabricated by placing filtering material to the bottom of the dis¬ posable drinking cup and subsequently inserting another drinking cup 3 of similar type to the inside of the first drinking cup, whereby the filtering material remains into the space 8 formed between the bottoms of the cups 2, 3. The conical shape of the cups 2, 3 permits insertable stacking of the cups, whereby the cup bottoms remain at different heights. To the bottoms 9, 10 are formed holes, which are further screened with meshes 5, 6. The cups 2, 3 are advantageously sealed together with an adhesive at point 7. Thus, an assembled filter part is formed which is suited for stacking over a third cup 1 acting as a drinking cup and filter support. After such an assembly, the filter-drinking cup combination is ready for use. The liquid to be filtered is poured into the receiving part 3 of the cup, wherefrom is flows by gravity via the mesh

bottom and the filtering material to the drinking cup 1 acting as the filter unit body part. The filter part can also be placed over any other vessel such as a coffee pot, or alternatively be held in the hand during the filtering operation.

A crucial and important factor for the effective function of the filter is a steady and sufficiently slow filtering flow rate. The ratio of the filtered liquid exit hole diameter to the filtering layer diameter should be 1:10, and to the thickness of the filtering material layer, 1:5.

The applications of the invention must not be understood to be limited by the embodiment described above, but rather, a plurality of modifications are possible within the scope of the inventive spirit disclosed in the annexed claims.