Patent ID: 7160452

Claim:
A filtration device comprising: a filtration tank, having an upper filtration media support member and a lower filtration media support member which are vertically separated, the upper filtration media support member supporting a layer of first particulate filtration media; and a cleansing mechanism, comprising: a vertically oriented hollow cleansing tank provided in the filtration tank; a cleansing means, for conveying the first filtration media upwards within the cleansing tank while cleansing the first filtration media; a contaminant expulsion means, for expelling contaminants separated from the first filtration media during cleansing to the exterior of the filtration tank; wherein: during normal filtration, liquid which has been filtered by the filtration media is passed through the upper filtration media support member and the lower filtration media support member and discharged therethrough; the upper filtration media support member comprises a great number of liquid passage portions, of a size which is difficult for the first filtration media to pass through; and a layer of second filtration media, which are greater in size than the first filtration media, is provided between the upper filtration media support member and the lower filtration media support member; and liquid spraying pipes, for spraying the second filtration media from the exterior, provided on the outer wall of the filtration tank, wherein a cleansing fluid is sprayed toward the layer of the second filtration media by the liquid spraying pipes, to separate contaminants attached to the second filtration media by the stream of cleansing fluid.