Air duct block for air/water underdrain systems in gravity filters

An air duct block for use in draining and backwashing a filtering media of a type where liquid may be passed downward through the media to an underdrain supporting said media, said underdrain including a plurality of parallel laterals, each lateral having an interior wall configuration defining at least one primary conduit and at least two secondary conduits, said air duct block comprising:

• a bottom surface;
• a top surface;
• a pair of sidewalls extending between said bottom surface and said top surface;
• a plurality of interior walls defining at least one lower water chamber, at least one upper gas chamber and at least one upper mixing chamber, said mixing chamber extending directly beneath the top surface;
• a plurality of apertures in said interior walls for providing communication between the water chamber and the mixing chamber and further providing communication between the gas chamber and the mixing chamber;
• and
• a plurality of dispersion orifices in said top surface providing communication between the mixing chamber and the filter media;
• at least one of said sidewalls having an opening therein providing means for transverse communication between said upper gas chamber and the upper gas chamber of an adjacent air duct block;
• wherein backwash gas is supplied to said gas chamber and backwash liquid is supplied to said water chamber during the backwash mode, said gas chamber and said water chamber being in communication with at least one adjacent underdrain lateral for providing backwash liquid and backwash gas thereto, said backwash gas and said backwash liquid further entering said mixing chamber and proceeding through the dispersion orifices in said top surface to cleanse the filter media directly above said air duct block.

A system for draining and backwashing a filtering media of a type where liquid may be passed downward through the media in a filtration mode to an underdrain supporting said media, said underdrain including a plurality of underdrain filter blocks placed end to end in parallel adjacent rows, each row defining a lateral, said system adapted to supply a backwash gas to the underdrain during a backwash mode for cleansing the media, said system comprising:

• a row of interconnected air duct blocks positioned below said filtering media and extending substantially transversely to said laterals, each air duct block having a bottom surface, a top surface, a pair of sidewalls extending between said top and bottom surfaces and a plurality of interior walls defining at least one lower water chamber, at least one upper gas chamber, and at least one mixing chamber with a middle partition extending between said sidewalls and parallel to said top and bottom surfaces, said interior walls having apertures therein for communication between the lower water chamber and the mixing chamber and further between the upper gas chamber and the mixing chamber;
• each air duct block in communication with at least one adjacent underdrain filter block to supply backwash gas to said underdrain filter block during the backwash mode;
• each air duct block having a transverse trough defined by an opening in said top surface and a cutaway portion in each sidewall, said trough further defined by a saddle assembly which is integral with said middle partition and with the interior walls which define said upper gas chamber, said saddle assembly having at least one aperture for providing communication between the upper gas chamber and said trough;
• an integral tube which is received by the troughs in each of said interconnected air duct blocks and which extends transversely to said laterals, said tube having apertures therein corresponding to the apertures in said saddle assemblies to provide communication between said tube and said upper gas chambers;
• a cover having a plurality of dispersion orifices therein extending above the trough in each air duct block and defining a mixing chamber above said tube, said mixing chamber in communication with the mixing chambers in said air duct block;
• means for supplying backwash gas to said tube;
• wherein backwash gas is supplied to said tube and backwash water is supplied to said lower water chambers during the backwash mode, said backwash gas entering the upper gas chambers in each air duct block through the apertures in said tube thus supplying backwash gas to the underdrain filter blocks of at least one adjacent underdrain lateral, backwash gas and backwash water further entering said mixing chambers through said interior wall apertures and then passing through said dispersion orifices to cleanse media directly above the air duct block.

A system for draining and backwashing a filtering media of a type where liquid may be passed downward through the media in a filtration mode to an underdrain supporting said media, said underdrain including a plurality of underdrain filter blocks placed end to end in parallel adjacent rows, each row defining a lateral, each lateral having at least one primary conduit and at least one secondary conduit, said system adapted to supply a backwash gas to the underdrain during a backwash mode for cleansing the media, said system comprising:

• a row of interconnected air duct blocks positioned below said filtering media and extending substantially transversely to said laterals, each air duct block having a bottom surface, a top surface, a pair of sidewalls extending between said top and bottom surfaces, and a middle partition extending between said sidewalls, said middle partition having a first portion parallel to said top and bottom surfaces and cooperating with said bottom surface to define a lower water chamber, with a second portion inclined with respect to said first portion, said middle partition defining a transverse cutout in the air duct block;
• a mounting flange extending from said top and bottom surfaces for engaging an adjacent underdrain filter block;
• an aperture connector on the second portion of said middle partition;
• an integral tube which is received by the cutouts in each of said interconnected air duct blocks and which extends transversely to said laterals, said tube having apertures therein for receiving said aperture connectors and providing communication between said tube and the primary conduit in an adjacent underdrain filter block;
• means for supplying backwash gas to said tube;
• wherein backwash gas is supplied to said tube and backwash water is supplied to said lower water chambers during the backwash mode, said backwash gas entering the aperture connectors to supply backwash gas to the underdrain filter blocks of at least one adjacent underdrain lateral, with backwash liquid entering said lateral through the lower water chambers.