| 摘要 |
A filter assembly comprises a volume occupied by a series of filter layers (P1-P4), each of which is designed to come into use when the next layer upstream has clogged, to avoid rapid clogging of the assembly. The assembly may comprise a series of porous paper filter sheets with grooves impressed therein to define apertures which are opened by the rising pressure when that sheet clogs to bypass the unfiltered fluid flow to the sheet downstream. Alternatively, a depth type filter is used comprising a bed of crumpled paper balls, rings, strips or ribbons, possibly coated with adhesive and packed into a net bag or perforate box, possibly with upstream and final filter stages.
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