| 摘要 |
Underdrain lateral system, which is especially adapted for use in a gravity filter bed, includes, as its preferred embodiment, scallop-shaped laterals having an upper, wrapped wire, slotted screen surface. The screen surface supports and retains the filter media particles directly, without the necessity of an underlying gravel layer, and is itself supported by channel-shaped rod members which are welded to the wires. The web portions of the channel rods perform the function of simultaneously distributing air and water during backwashing, and include small apertures in upper channels and larger apertures in lower channels to cause a plenum to be formed inside the laterals which ensures that the distribution of air and water will be uniform throughout the lateral, even if the lateral is not perfectly level. Distribution of the air and water throughout all of the laterals is made even more uniform by mounting the laterals on a header and providing perforated flow tubes which extend from each lateral into the header to produce an additional air plenum therein.
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