| 摘要 |
A plurality of hollow filter sheets have a suction pipe inserted therethrough to be stacked with a ring-shaped packing clamped therebetween. Therefore, a gap between the hollow filter sheet and the suction pipe is watertightly sealed. In the hollow filter sheet, a hollow portion is provided between two filters, and then a spacer with a surface having pits and projections is provided in the hollow portion. A narrow passage space allowing liquid to pass through is provided between the filter and the spacer by pressing the two filters against surfaces of the spacer with the packings and causing the filters to be deformed into a shape according to the surfaces of the spacer. The narrow passage space is smaller than a drainage space between the filters and the spacer that are not clamped by the packings.
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