
The height limit of a siphon - monort
http://www.nature.com/articles/srep16790
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matthiasl
A longer summary: the maximum height of a siphon pumping water, at sea level,
predicted by barometric pressure is about 10m.

But the tensile strength of water is nonzero (a surprise to me) and that is
enough to allow much higher siphons if you first remove dissolved gases from
the water.

The paper speculates that several hundred metres may be possible, perhaps even
more. The paper also describes an actual experiment where they showed that a
15 metre high siphon works in practice.

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venomsnake
What are the practical implications of higher siphons?

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johnm1019
IANA fluid dynamics expert, but it seems to me that for certain designs which
move water by creating a lower pressure at some point inside of a pipe you've
created a "siphon" in a general sense. If that's true, this could affect
certain water pump and plumbing designs, albeit this degassing process may be
prohibitively expensive.

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Gravityloss
Closed circulation central heating systems are degassed. Though, the water is
hot there so boils much more easily. Maybe closed circulation cooling water
systems...

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chadnickbok
Relevant xkcd what-if: [http://what-if.xkcd.com/143/](http://what-
if.xkcd.com/143/)

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aaron695
Except he has gotten it wrong hasn't he?

Which I guess is why this is trending.

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gefh
His note [5] links to
[https://www.youtube.com/watch?v=8F4i9M3y0ew](https://www.youtube.com/watch?v=8F4i9M3y0ew)
which is a demonstration of a siphon in a vacuum, so he's covered :)

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Dylan16807
But working "a little bit" as the note says is a good way off from working an
order of magnitude or two better.

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emmelaich
My summary: the limit is much higher than can be predicted by barometric
pressure because of the tensile strength ("surface tension" of water)

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glup
So this is why I couldn't siphon (gray) water from my bathtub on the third
floor to water plants in the yard, not lack of moral fortitude. Great!

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jeremysmyth
No, unless the water had to _rise_ 10m from your bathtub before descending. If
it only had to rise enough to climb through a window before descending to your
yard, then that is not enough to produce the problem in the article.

The problem described is that water cannot be lifted _up_ more than 10m (due
to air pressure pushing on the bath side not exceeding the weight of 10m of
water in the hosepipe), not pulled down on the far side.

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basicplus2
yet but no..

1\. bottom of siphon outlet has to be sealed by the surface of water held in a
container.. and

2\. and height of long side must less that atmospheric pressure in height from
said surface of water

or water column on down side will break and draw will be lost

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LeifCarrotson
But the bottom side of the siphon doesn't have to be the bottom of the system.
Run the tube up 1m to the window and back down out the window perhaps 3m to a
bucket on the porch roof - an easy, simple, working siphon. From that bucket,
you can use a regular positive-pressure bottom drain to go down as far as you
like.

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iandanforth
I love this classic science. Theoretically this experiment could have been
performed in the 19th century!

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mabbo
This is why water is pumped from below pushing up rather than pulling from the
top. But perhaps this will open up new ways to make water pumping more
efficient.

