Cap system for underdrains in gravity filters

A capped filter underdrain block for a filter system having a filter bottom with a plurality of underdrain distributors extending in parallel rows across said filter bottom, each distributor comprising a plurality of underdrain blocks placed end-to-end, with a filter media supported on said underdrain blocks, said capped filter underdrain block comprising:

• a block having a bottom wall, a top wall and a pair of side walls extending therebetween, said block having at least one mixing conduit therethrough, said top wall having a plurality of orifices in communication with said mixing conduit for receiving effluent from said filter media in a downflow mode and for discharging a backwash fluid in an upflow mode;
• a cap having a top surface and a bottom surface, with a plurality of spaced screen members on said cap, said screen members defining a plurality of slots in the top surface of said cap, said slots sized to provide fluid communication between the filter media and the orifices in said top wall without passage of filter media therethrough;
• said slots defining means for uniformly distributing backwash fluids across the top surface of said cap and for extended intermixing of backwash fluids;
• said screen members inclined with respect to the horizontal to define integral raised portions in said top surface.

A capped filter underdrain distributor for a filter system having a filter bottom with a plurality of underdrain distributors extending in parallel rows across said filter bottom, said distributor supporting a filter media disposed above the distributor, said capped filter underdrain distributor comprising:

• a plurality of inclined walls defining at least one primary conduit and at least one mixing conduit therethrough;
• a top horizontal wall having a plurality of orifices in communication with said mixing conduit, with a plurality of ribs defining a plurality of sectors;
• a cap having a top surface and a bottom surface, with a plurality of spaced screen members on said cap, said screen members tapered in the direction of said bottom surface and defining a plurality of slots in the top surface of said cap, said slots sized to provide fluid communication between the filter media and the orifices in said top wall without passage of filter media therethrough;
• said slots and said ribs defining means for uniformly distributing backwash fluids across the top surface of the cap;
• and
• said screen members inclined with respect to horizontal to define integral raised portions in said top surface for extended intermixing of backwash fluids.