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RE: More end-of-tank-dump comment -- or - Writing Checks for Checkvalves

>For anyone who's still interested in this thread ...
>[exp details deleted]
>After 30 minutes it will climb up about 3 feet.
>After an infinite amount of time (well ... overnight anyway) it climbs up
>to around 4-1/2 feet.

>Interestingly, it doesn't collapse the remaining, water-free tubing -
>unlike what I see in my aquarium CO2 set-up..

Not enough pressure. I don't have any specs on vacuum ratings for regular 
aquarium airline tubing (silicone or vinyl), but it should be high enough 
that a water column in the tubing won't be a problem.

>I assume that the reason the water column only goes up to 4-1/2 feet is
>because the weight of water causes a pressure reduction in the remaining
>1-1/2 feet of CO2 which balances the waters ability to further absorb any
>more CO2.  So in a real system, with the cylinder beneath the aquarium &
>where the water would enter at the top & the weight of water is pushing
>DOWN on a static column of CO2, I guess the water would eventually
>completely fill the tube?

Atmospheric air pressure is only able to force a water column up so far in 
any given vertical passage. That's the big reason why pumps can usually 
push water a lot higher on their output than they can lift water on their 
intake. Normal atmospheric pressure is about 14.5 PSI at sea level, so 
unless you have other factors involved (capillary action, thermal forces, 
etc.), that's the most pressure that will be involved in an experiment like 

Also, the CO2 will both diffuse through the tubing and dissolve into the 
water, but won't ever make a complete vacuum in the top part of your tube 
-- there will always be some gas in there, so the tube will never 
"completely" fill with water.


>I suppose that tells me that anyone with a CO2 system which, at any time,
>has the CO2 shut-off (like in a pH controlled system or if the cylinder
>runs empty) is at risk of having water pulled back into the regulator &
>cylinder unless they have a check-valve.
>I might test that hypothesis tonight, if I have time, by swapping the
>location of the container of water to the top of the airline.
>Regards, Kevin

Waveform Technology
UNIX Systems Administrator