Floating Bead Filter
Operation
The filter is a copy of a commercially produced pond filter.  It uses 2 cubic feet of raw polyethylene pellets floating at the top of the canister as a filter material.  Water enters from the bottom of the filter and flows up through the cake of beads which provides the filtering action.  A bead filter will not provide the "polishing" of a pool sand filter or even more so a diatomaceous earth filter.  Those are much less practical however, as they would require more frequent cleanings and sand filters cake up and channel the water as opposed to filtering it.  This filter is also designed to hold 2 cubic feet of a sinking plastic bead.  The sinking beads are suspended by the up flow of water producing a fluidized bed.  Fluidized beds are very efficient biological filters.  I found that the biological activity of the floating beads were more than adequate and did not add the sinking beads.  The filter is equipped with a pool type multi-port valve, making backwashing and rinsing very easy.  In addition a spa type blower is added to improve the efficiency of backwashing.  After the beads are broken up a little bit by backwashing, the pump is shut and the blower run while the multi-port valve is set to rinse.  Air is forcefully blown into the filter from the bottom and leaves through the upper filter arm.  The action of the air breaks up the beads and trapped dirt making backwashing and rinsing more efficient.
Construction

     

The filter started out as a stainless steel diatomaceous earth filter made by Pac Fab.  The internal DE screens are removed and replaced by simple PVC parts.  Water enters and exits the 2 inch PVC through slots made on a table saw.  The slots are just small enough so the polyethylene beads can not get through.  Water enters the filter from the bottom through the spinner assembly.  It doesn't spin, but is simply PVC heated and bent to impart a circular motion to the water entering the filter.  Water is prevented from going through the waste "T" assemble by a check valve.  Water exits the filter through the spray bar assembly on top which is encased in 2 cubic feet of beads during operation.  Backwashing forces water from the spray bar down through the beads and out through the waste "T" assembly, the check valve opening with water flowing in this direction.  Cost to build the filter was several hundred dollars less than wholesale price of the commercial unit and less than half of the retail price.  The filter has worked so well that I converted a large sand filter into a bead filter for my koi pond.

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