"Bruce" wrote in message
oups.com...
I am trying to use a 4" flexible corrugated plastic pipe to siphon from
my pond into a small pool and then to a stream bed. I have no problem
getting the flow going, but after a few days the flow rate goes down.
Then after about a week it stops altogether.


Siphons are incredibly difficult to maintain. If the fill rate into the
suction side does no keep pace with the suction from the siphon, then the
water level will slowly drop and the siphon will suck in air. Or if debris
temporarily clogs the siphon entrance, the vacuum could suck an air bubble
in from the discharge side and break the siphon as well.

You may have to reengineer a solution that does not rely on a siphon. Pump
fill and gravity return is the most reliable. (Again provided a leaf or
something doesn't clog the return line)

-S