Slow sand filter float valve flow control device in filter 3 and filter 2
The pvc pipe is 1/2 inch. There are .040 inch holes drilled on the bottom of the pipes to allow the water to disperse without disturbing the sand surface.

The float valves limit the volume of the flow of input water so it matches the volume of the flow of water through the filter. As the filters "ripen"
their flow rate will slow down. The float valves will, by their nature of operation, slow the flow of water down equally.
The drawing below is of filter 3, the filter 2 drawing with the float valve installed is not yet done.

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This is the newest float valve installed in filter 2. Note the "schmutzdecke" (dark color) on the white sand. (This is not usually visable on all functioning filters)	This is filter 3 with the float valve installed.
The "schmutzdecke" is not necessarily visible on all filters. Filter 2 has deliberately not been cleaned specificaly for the purpose of illustration and testing so it is possible to see the accumulation of substance that occurs over time. "Schmutzdecke" is just a fancy word for the top biolayer that does most of the work purifying the water.
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