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homebrew hydro update: coanda water intake - Page 7

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Posted by harry on February 28, 2009, 7:57 pm

Another useful idea. I saw this in Egypt.  To control the outflow from
your dam, avoiding picking up trash in the water,
Run a hose pipe through tthe base of the dam (one long enough to reach
the surface of the water on the "lake/pond".  Now take a sealed  oil
drum (for a float) and fasten it to the end of the hose so that it's
suspended  below the surface.
As the water level in the dam changes, the hose inlet rises and falls
as required.
As the hose is not on the bottom of the pond or on the surface,
niether floating or sunken debris is picked up.
Regardless of the water level in the dam, the outlet pressure remains
fairly constant.
To shut off the water, just lift the hose & float above water level
and set it on the bank.
Works best with a PVC hose that's not to flexible, (You don't want the
hose to kink.) ie like the stuff you bury in the ground for a water
supply. At least we do over here in the UK
Simple, cheap and foolproof.  Works well
Clever these Arabs what?

Posted by Tim Jackson on February 28, 2009, 8:20 pm
harry wrote:

You can achieve essentially the same effect with a short stand-pipe on
the bottom of the pool, with the advantage that the outlet pipe doesn't
have to flex in normal operation (although flexibility may be useful for
maintenance - it will need lifting out of the silt now and again).

With either system the outlet pressure head is the same, it is the level
of the water in the pond.

I use that method to feed a fountain from a spring: along with a simple
strainer over the intake it is quite effective at preventing the 2mm
nozzles from blocking. Maybe once or twice a year a worm manages to
reach and squeeze through the strainer, and get itself stuck (and very
dead) in a nozzle.  Messy.

Tim Jackson

Posted by z on February 28, 2009, 9:50 pm

Had I not been an idiot when I had the pond dug i would have had a big
pipe plumbed through the base of the pond with a large perferated riser
that reached above the level of the pond.  Then you put a float inside
the riser so if the water is used up to where the pond is nearly dry the
float would seal over the pipe and stop you from draining it completely
.. and preserve the siphon.

But like an idiot I didn't think of that when I had the pond dug, so now
i'm too paranoid to dig one in with the thing full of water.  It holds
water so well now I figure if I break the pond down to put in the pipe
i'll risk never having it hold water again :)  I mean now it holds water
all summer .. it kicks ass.  If it ain't broke don't fix it kind of

So it goes

but the floating barrel idea .. now that one I might put into action,
just don't want to dig into things too much



Posted by Tim Jackson on March 1, 2009, 12:41 am
 z wrote:

It's the same both ways. If the pipe floats say a foot below the barrel
then it's OK till the water gets down to a foot, then it sucks dirt and
blocks.  With a foot high standpipe, when it gets down to a foot of
water, it sucks air (and/or duckweed), and breaks the syphon if you have

The seal thing is possible but tricky, I experimented with that when I
first did the fountain with about a 20' head, it wasn't easy to get
something to seal that well after a few months exposed to algae, other
lifeforms and neutrally buoyant debris, so it generally broke the syphon
anyway. I had a standpipe strapped to a slab of rock and a cord to haul
it out when things went wrong.

So now I have the fountain flow set below the summer minimum spring
rate, bottom exit - no syphon, a shut-off valve and silt-dump valve for
maintenance, so now it never airlocks and will self-start even if it does.


Posted by z on March 3, 2009, 6:17 am

yeah I had a design in mind and have the parts .. I was going to use a
toilet float (which fits nicly into a 4 inch pipe) covered in some rubber
paint so it'd make a good seal.

But man .. even when drained I can't walk into my pond to do any work.  
Its all blue clay and just about the nastiest, stickiest stuff you can
imagine.  If you walked in there to do some work without it baking in the
sun bone dry for at least a month you may never walk out.. I guess thats
why it holds water so good.  Double edged sword.

So I gave up on ever doing anything that required me to get into the
middle of that thing.. even built some scafolding to try and get in there
but its like one of those situations where if you get stuck, 10 million
years later scientists are pleased at finding such quality preserved
specimens :)

so the float barrel idea seems like the thing to try :)

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