filtre à vitesse décroissante

CONT: [...] réalisation, dans certains cas, soit de filtres à vitesse décroissante (double filtration, filtres, dual media filter), soit de filtres à granulométries différentes.

CONT: The design of gravity rapid sand filters shall be based on a maximum design filtration rate of two gallons per square foot per minute. As the beginning of filter runs for declining rate filters, a maximum filtration rate of three gallons per square foot per minute is allowed. The filter discharge piping shall be designed with an orifice or other permanently installed flow limiting device to ensure that the maximum filter rate cannot be exceeded... With the exception of declining rate filters, each filter unit shall be equipped with a manually adjustable rate-of-flow indication or control valves with indicators.