| 摘要 |
A sheet of porous filter material folded into accordion pleats, the pleats having opposite edges folded over on diagonal fold lines to close the opposite edges of alternate pleats. The pleated and folded sheet is selectively disposed in flat panel form or formed into a tube with the pleats extending axially of the tube. When the filter is in its tubular form, the folded pleat ends are disposed at the exterior of the tube.
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