How about extra tank between pond and filter with ball cock valve installed,
water in filter drops ball valve opens, water rises ball valve closes, have
the tank and filter at same level and connected below water surface.
Also run submersible pump to first tank, through the ball valve, this will
ensure sufficient flow even if water level drops in pond. you can fit two
port valve so that some water is pumped back into pond as bypass.


"Etienne" wrote in message
ups.com...
Hi guys,
My koi pond and my filter are on different levels - difference is about
70 cm.
I am looking for a solution to regulate the water stream from the pond
to the filter in such a way that the water throughput , regulated by a
valve/shutter, is depending on the water level in the filter. I have
been looking for an electrical valve but most of these valves need more
pressure than 70cm of water can generate; and the low-pressure
operating valves are expensive.
Has anybody already solved such a construction, possibly made a
mechanical valve himself?

I see a possibility to work with an overflow threshold in the upper
part of the pond - but this means that I am only getting surface water
in the filter and that I am very depending on the waterlevel in the
pond ( evaporation in summer!).
I could make a hole in the pond near the level of the filter but if the
filter pump fails my pond will loose all its water, and the calibration
of the right flow of water through this canal seems not
straightforward.
You see I do not have a reliable solution yet, is there anybody with
good suggestions?


H~~level pond~~H---terrace-----H
H ~~~~~~~~~~ H
H H
~~ ======= Valve to be H
. H placed
. H

H """'''lawn'""H~Lvl filter~ H
H H ~~~~~~~~~ H
H H H