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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 ...

Last night I did a little experiment.

- Take a 6ft length of silicone airline.

- Fill it with CO2 & put a clamp on both ends.

- Suspend it from a suitable high place with the bottom end submerged in a
container of water.

- Remove the clamp from the bottom end.

What happens is that a column of water slowly starts to climb up the

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..

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?

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

>Hi Kevin,
>     I'll take a stab as to how the airline between your solenoid and
>valve is getting sucked flat...
>     A lot of solenoids generate a considerable amount of heat when they
>operating, or open. It would stand to reason that this would heat the CO2
>travelling through them. When the power is cut, the valve closes, and the
>CO2 ceases to be heated. As the CO2 trapped between the closed solenoid
>the closed check valve cools, it shrinks in volume, sucking the flexible
>silicone hose flat in the process.
>     This is just a guess, but I can't think of how else it could be

If this is the case, winding a spring of stiff wire (like some paperclips,
or some maybe 22awg steel wire from a hardware store) around the tubing
where it's going flat should help to keep it open. Round tubing deforms to
an oval when "sucked flat", so if you prevent it from enlarging in one
dimension you can keep it open. It's a simple trick that I've seen used on
a lot of tubing benders for semirigid copper tubing.

I agree that it is unlikely that you would be able to build enough vacuum
pressure with aquarium equipment to flatten even the soft silicone airline


>Best regards,
>Ron Barter
>Perth, Ontario