| 摘要 |
<p>A precast concrete, plastic-jacketed filter underdrain block (20) for downflow filter units is disclosed. The jacket (26) functions as a mold for the concrete (36) and becomes an integral part of the underdrain block (20). Thus, lightweight, inexpensive plastic molds (26) can be fabricated and shipped to the filter construction site where they are filled with concrete, cured, and then placed in the filter unit (8) to provide an underdrain system. The underdrain blocks (20) may have handholds (44) to facilitate their handling and may be provided with alternating vertical rigs (40) on the outside vertical surfaces of the plastic jacket (26) which create an interlocking system; whereby when installed in the filter unit (8) each block (20) is interconnected to its adjacent side blocks creating a uniform interconnected filter underdrain system which resists the uplifting and displacement of individual blocks during backwashing operations.</p> |
