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Does anyone think you could possibly make a syphon that had a bypass that just circled back into the pond creating an aerator??[


Siphon flow depends on a pressure gradient. Specifically, the pressure at the syphon outlet must be less than the equivalent elevation in the reservoir. When the end of the syphon is connected to the reservoir the pressures are the same and so there will be no flow. The concept you imagined is but one of many imagined "perpetual motion " or "free energy" machines. They seem plausible until one considers the physical laws at play.

It isn't what we don't know that gives us trouble, it's what we know that ain't so - Will Rogers