| 摘要 |
Filtering apparatus of the sand-circulating type in which the backwashing conduit means, by which the filtering medium is circulated from the bottom of the bed to the top and washed in the process, are located around the periphery of the vessel. The conduit means may comprise a series of tubes, each associated with a water jet and equispaced around the vessel wall. Emerging from the tubes, the washed medium may be constrained to pass radially inwards between upper and lower guiding baffles before finally falling onto the top of the bed. The support plate on which the bed rests may be upwardly conical in shape, may contain water nozzles to help direct the lower part of the bed towards the backwashing conduit, and may be formed with perforations through which filtrate may pass. The distribution of perforations across the support plate may vary progressively, being least at the vessel axis and greatest close to the vessel wall, to help promote an even rate of flow of filtrate through the bed across its entire area. |
