Abstract: The present invention relates to a filter provided with a filter bed consisting of a granular material, which does not comprise layers of coarser material. In the filter bed at least one liquid distributor is arranged which defines an expansion space otherwise defined by areas of repose for the bed material, in which space at least one outflow opens above the areas of repose. The distributor is so designed, that the liquid can flow out of the openings with great energy and fill the cavity and fluidize the whole bed, which enables homogenous rinsing of the bed. The opening of the distributor is larger than the mean grain size of the filter bed material and allows fiber, pieces of plastic and similar impurities to pass through the distributor and be removed from the filter.

Abstract: An underdrain is provided in a water filtration system beneath a bed of filter media and comprises a plurality of elongate hollow underdrain units defining respective elongate substantially horizontal fluid passageways therein with the hollow underdrain units being arranged with the elongate fluid passageways thereof in fluid communication with each other and forming a network of fluid passageways beneath the bed of filter media. Each underdrain unit is provided with a plurality of nozzles in the upper wall thereof communicating with the interior of the hollow underdrain unit and with at least some of the nozzles in each underdrain unit cooperating with each other and being arranged in spaced groups. The cooperating nozzles in each group are so oriented as to direct streams of wash water issuing therefrom during backwashing into impingement with each other outside the filter underdrain unit for dispersing the streams of wash water and reducing the velocity thereof.

Abstract: The disclosed method and apparatus relate to the rejuvenation of a bed of granular filter medium which has accumulated particulate and lint contaminants during filtration flow of dirty liquid. The method first includes the step of agitating the filter bed to break-up contaminants which have become agglomerated. The agitating step includes flowing the filter granules and the contaminants in a liquid mixture slurry from the filter bed housing through a closed flow path and then back to the filter housing. The bed is then at least partially reformed, with the finer particulates and lint being in the upper portion of the bed and the larger particulates being in the lower portion of the bed. Then, the upper portion of the bed is expanded and backwashed to remove the finer particulate contaminants and lint. At the same time, the lower portion of the bed and the heavier contaminants flow in a liquid mixture through a cleaning element to remove those heavier contaminants.