| 摘要 |
PROBLEM TO BE SOLVED: To solve such a problem that in order to form a uniform precoat layer on each of precoat-type elements 22, a precoat process conventionally has to be performed in three steps using third piping 13 in addition to first and second pipings 11, 12 in the early stage of the precoat process. SOLUTION: This precoat system S consists of first piping 11 for supplying slurry from a precoat tank 10 to a filter vessel 21, second piping 12 for returning penetrating water from precoat-type elements 22 to the precoat tank 10 and third piping 13 for xtracting diluting water before penetration from the top of the filter vessel 21 and returning the water to the precoat tank 10. In addition, the system S forms an ascending water flow in the filter vessel 21 using the third piping 13 in the early stage and the terminal stage of the precoat process. In this system S, the third piping 13 is omitted and a water passage pipe 27 is installed at a position surrounded by the precoat-type elements 22 in the filter vessel 21. Thus a descending water flow opposed to the ascending water flow from an inlet pipe 21C through the water passage pipe 27 in the filter vessel 21 (an upper chamber 21B) is formed.
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