Patent ID: 8070946

Claim:
An apparatus for use in a filter system for filtering water or wastewater, said apparatus comprising: (a) an underdrain lateral, said underdrain lateral having at least a first chamber, a second chamber and a third chamber, said third chamber being disposed below a lowermost portion of at least one of said first chamber and said second chamber, said underdrain lateral further including an inner wall, an orifice being formed in said inner wall to permit a gas to pass from said second chamber into said first chamber, said orifice being disposed between an upper surface and a lower surface of said second chamber, said inner wall having an orientation other than horizontal; (b) said first chamber being configured to simultaneously direct a liquid and a gas into a filter bed during a first washing procedure including simultaneous use of a liquid and gas to clean the filter bed; and, (c) said second chamber being configured to direct only a gas into a filter bed during the first washing procedure while said first chamber is simultaneously directing a liquid and a gas into a filter bed during the first washing procedure.