Filtering device

Details Filtering device Filtering device

1999-02-26

2002-12-03

Savage, Matthew O. (Department: 1723)

Liquid purification or separation

Flow, fluid pressure or material level, responsive

Check valve

C210S275000, C210S284000, C210S289000, C210S291000, C210S323200, C210S315000, C210S317000, C210S333010, C210S335000, C210S338000, C210S355000, C210S411000, C210S415000, C210S458000, C210S489000, C210S499000

Reexamination Certificate

active

06488842

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to a filtering device and, more particularly, to a filtering device suitable for precision filtering in a state submerged in liquid to be treated. Liquid to be treated includes water for general uses, drinking water, river water, pool water and various other liquids.
Known in the art of filtering devices is one which comprises multi-layered filtering materials of different types provided in a single container through which liquid to be treated is subjected to different filtering operations. One example of such prior art filtering device is shown in FIG.
19
. In this prior art filtering device, liquid to be treated is introduced into a container a through an inlet b provided in the upper portion of the container a. The liquid to be treated is spread over an upper filtering material layer d through distributors c. The upper filtering material layer d consists of coarse grains of anthracite and impurities of a relatively large diameter in the liquid to be treated are trapped by the anthracite layer. Then the liquid to be treated flows down through the lower filtering material layer e which consists of fine grains of garnet and impurities of a smaller diameter are trapped by the garnet layer. The treated liquid is collected by a collector screen f and discharged from an outlet g provided in the bottom portion of the container a.
Since most impurities in the liquid to be treated are trapped by the upper layer in this prior art filtering device, the anthracite grains of the upper layer tend to be easily blocked by the impurities and, therefore, frequent reverse washing of the upper layer is necessary. For this purpose, compressed air is blown into the upper and lower layers d and e through the collector screen f to stir the filtering material grains of the upper and lower layers d and e and thereby remove the impurities and then reverse washing water is forced into the upper and lower layers d and e through the collector screen f to wash away the impurities. This reverse washing must be performed accurately because otherwise the impurities, once removed from the anthracite grains but left in the container without being washed away, will fall on the surface of the upper layer d and are deposited thereon.
Another problem in this prior art filtering device is that, since the diameter of a filtering material of the upper layer d is generally larger than the diameter of a filtering material of the lower layer e, if the filtering material of the upper layer d is of the same specific gravity as the filtering material of the lower layer e, the filtering material of the upper layer which is of a larger diameter settles sooner than the filtering material of the lower layer e after stirring of the filtering materials made during the reverse washing operation with the undesirable result that the filtering material of the upper layer d is deposited under the filtering material of the lower layer e. For preventing occurrence of this phenomenon, in the prior art filtering device, coarse grains of anthracite which is of a smaller specific gravity than garnet are used in the upper layer d and fine grains of garnet are used in the lower layer e. Thus, selection of filtering materials for the upper and lower layers is limited by the specific gravity of the filtering material.
More importantly, the prior art filtering device has a relatively small effective filtering surface area in comparison with the size of the container in which the multi-layered filtering materials are provided.
It is, therefore, an object of the present invention to provide a filtering device which has a larger effective filtering surface area than the prior art filtering device.
It is another object of the invention to provide a filtering device which is capable of reducing the amount of impurities deposited on the surface of a filtering material and thereby reducing frequency of a reverse washing operation.
It is another object of the invention to provide a filtering device in which selection of two or more different filtering materials can be made freely without being limited by the specific gravity of the filtering materials to be selected.
Other objects and features of the invention will become apparent from the description made heinbelow with reference to the accompanying drawings.
SUMMARY OF THE INVENTION
For achieving the above described objects of the invention, there is proivded a filtering device comprising a container having an inlet for introducing liquid to be treated, an annular multi-layered prepacked screen assembly provided in said container and having an outlet for treated liquid, said screen assembly comprising three or more cylindrical screens having different diameters and being coaxially disposed in said container with their axes extending vertically in said container, an annulus being formed between respective adjacent cylindrical screens, and two or more different filter materials performing filtering functions which are different from each other and being filled one in each of the annuluses between the cylindrical screens.
According to the invention, an overwhelmingly larger effective filtering surface area than the prior art filtering device is available owing to the structure of the filtering device as defined in the claim. For example, as will be described more fully later, more than ten times as large effective filtering surface area as the prior art filtering device can be obtained in a case of using a container having a diameter of 2 meters and a height of 2 meters.
Further, since screen assembly is vertically disposed in the container, the liquid to be treated enters the vertically disposed screen surfaces of the cylindrical screens. This allows some part of impurities in the liquid to be treated to fall to the bottom of the container due to gravity before entering the cylindrical screens with the result that the amount of impurities trapped by the filtering materials of the cylindrical screens is thereby reduced. As a result, frequency of a reverse washing operation for removing trapped impurities is reduced as compared to the prior art filtering device in which all impurities of the liquid to be treated are trapped by the filtering materials and the working efficiency of the filtering device can thus be improved. Impurities which have settled on the bottom of the container can be removed periodically by opening a drain port provided in the bottom of the container.
Since the filtering materials are prepacked in the cylindrical screens of the annular multi-layered prepacked screen assembly in the form of a cartridge, replacement of the filtering materials by new filtering materials can be made simply by replacing the entire screen assembly and this replacement work will be much easier and less time consuming than in the case of the prior art filtering device in which the filtering materials must be replaced one layer after another.
Since the two or more different filtering materials are partitioned from each other by the cylindrical screens, there is no likelihood of mixing of the different filtering materials with each other during the reverse washing operation. Accordingly, it is not necessary to select, as in the prior art filtering device, filtering materials of different specific gravity for preventing reverse resettling of the filtering materials and, therefore, any desired filtering materials of different filtering functions can be combined freely without considering the specific gravity of each filtering material. This will enable a combination of filtering materials which will achieve a more efficient filtering result at a reduced cost.
Furthermore, since impurities removed from the filtering materials by the reverse washing operation will be completely washed away or fall to the bottom of the container due to gravity and will never return to the surfaces of the filtering materials, efficiency of the reverse washing operation will be improved as compared to the case of the prior art in which some of impurities removed from the filtering

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