Patent ID: 6569328
Filing Date: 2003-05-27
Classification: B01D,Y10T

Abstract:
In an underdrain filtration system which includes metal underdrains comprising a series of elongated perforated metal rib structures fixed against a floor and formed by bending so as to extend upwardly from the floor to define a filtrate plenum between the elongated rib and the floor, into which filtered liquid flows after passing through a bed of filtration media and through the perforations in the elongated rib structure, the improvement comprising:a series of stampings in the metal rib structure forming the perforations, which comprise slits positioned in arrays so that a plurality of such slits generally form a circuit, such that at each array a raised disc extends out from a surrounding flat area of the underdrain rib structure, the raised disc being integrally connected to the surrounding flat area by metal bridges positioned between ends of adjacent slits and which are left remaining from the stamping of the discs, and the slits defining said perforations in consistent width dimensions from slit to slit and from array to array, whereby consistency in the perforation size assures proper and consistent pressure drop through the underdrain and proper balance of liquid flow during backflushing of the underdrain, and whereby the raised discs cause a diverging pattern of backwash liquid flowing out of the underdrain and through the filter media when the underdrain is backflushed.