Baffle and wash trough assembly for granular-media filters

Water filtration apparatus of the kind providing a vertically-extending tank having a filter medium bed of granular filtering material in the lower portion thereof, underdrain means beneath said bed for collecting filtered water passing downwardly through said bed, and means for backwashing said bed of filtering material under high-turbulence, said high-turbulence backwashing means including means for passing water upwardly through said bed and aeration means for agitating said filtering material while said backwash water is being passed therethrough, wherein the improvement comprises at least one baffle, and backwash trough assembly for reducing filtering material loss during backwashing, comprising:

• a. a backwash water collection trough supported in said tank to extend horizontally across the upper portion thereof, said trough having upwardly-extending side portions and an upper edge on at least one side thereof functioning as an overflow weir, and the lower portion of said trough converging downwardly and inwardly from each side thereof;
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• b. substantially imperforate arcuate baffle means mounted adjacent to said one side of said trough in spaced relation thereto and extending horizontally along said weir edge, said baffle means having an upwardly concave portion in opposed relation to said trough lower portion on said one side thereof, said baffle means also including a portion extending below said trough bottom and a portion extending to a level above said weir edge, said baffle means providing an open-bottom restricted flow channel into said trough for backwash water, said lower and upper portions of said baffle means providing channel portions, respectively, of converging cross-section below said opposed portion and diverging cross-section hereabove.

Water filtration apparatus of the kind providing a vertically-extending tank having a filter medium bed of granular filtering material in the lower portion thereof, underdrain means beneath said bed for collecting filtered water passing downwardly through said bed, and means for backwashing said bed under high-turbulence, said high-turbulence backwashing means including means for passing water upwardly through said bed and aeration means for agitating said filtering material while said backwash water is being passed therethrough, wherein the improvement comprises at least one baffle and backwash trough assembly for reducing filter material loss during backwashing, comprising:

• a. a backwash water collection trough supported in said tank to extend horizontally across the upper portion of said tank, said trough having upper edges on both sides thereof functioning as overflow weirs, the lower portion of said trough converging downwardly and inwardly from each side thereof;
• b. first arcuate baffle means mounted adjacent one side of said trough in spaced relation thereto and extending horizontally along its weir edge, said first baffle means having an upwardly concave portion in opposed relation to said trough lower portion on said one side thereof, said first baffle means also including a portion extending below said trough bottom and a portion extending to a level above said weir edge to define a restricted flow channel into said trough for backwash water, said lower and upper portions of said first baffle means providing channel portions, respectively, of converging cross-section below said opposed portion and diverging cross-section thereabove;
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• c. second arcuate baffle means supported adjacent the other side of said trough and extending horizontally along said second weir edge, said second baffle means having an upwardly concave arcuate portion in opposed relation to the other side of said trough lower portion, said second baffle means also including a portion extending to a level above said second weir edge to define a second restricted flow channel into said trough for the backwater, the lower end of said second baffle means terminating above and spaced from said first baffle means, said second channel having its minimum cross-section within the portion thereof between said opposed portion of said second baffle means and said trough bottom portion, the cross-section of said second channel enlarging upwardly from said minimum cross-section.