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Re: Re: End-of-tank-dump comment -- or - Writing Checks for Check valves

Scott said:

"It depends on your setup ... the water might only travel a
short distance because, with nowhere to go but to compress
within the CO2 line, the pressure will build until it is
just enough to stop the water."

I'm not convinced that this is the mechanism.

If I completely close the valve on the CO2 cylinder & also shut-off the
solenoid valve then water still slowly climbs up out of the bubble counter
& down the airline until the airline between the bubble counter & the check
valve is FULL of water.  At the same time the airline between the solenoid
valve & the check valve becomes compressed TOTALLY flat; i.e. ALL the gas
has gone out of the airlines between the solenoid & the bubble counter.

My assumption is that the CO2 is continuously absorbed into the advancing
water column as it creeps down the airline (I assume also that it diffuses
out again at the ultimate other end of the water column where it meets the
aquarium water - otherwise I guess the water would become saturated with
CO2 & this process would stop?  Presumably the water in the bubble counter
is always saturated with CO2 whilst the CO2 is flowing?).

I only notice this because the way I have the flow rate set means that,
when the solenoid valve is open, CO2 is rapidly injected into the tank but
after the solenoid valve closes (when the correct pH is reached) it takes
much, much longer for the CO2 to diffuse back out of the aquarium.  So,
most of the time, I have the CO2 shut-off.  This isn't for any reason -
it's just fiddly to change it & I haven't had the time to do it!

FWIW - I don't have any leaks & the reactor I have is NOT into my external
filter & is arranged so that there is no "back pressure" that could push
water down the airline (I know this to be true because if I disconnect the
airline between the reactor & the bubble counter from the bubble counter NO
water is pushed back up that section of airline).

Regards, Kevin

Rod said, in part:

>  As
> soon as the gas is turned off on my CO2 water starts
> running up the line
> from the reactor towards the regulator. Obviously I have
> never let it get
> that far but I am assuming that if it did it would ruin
> my regulator.
> My assumption is that, if I didn't have the RF check
> valve (#1), eventually
> the water would be sucked-back through the solenoid valve
> & into the
> regulator as all the residual CO2 gets absorbed.

It depends on your setup  and a few different factors.
Take a perfectly normal setup with an external reactor
hooked up to a canister filter.  The water is under
pressure form the filter pump.  Also, if the CO2 tank is
below the aquarium water surface, gravity is working to
push the water down the CO2 line too.  If the gas pressure
on the CO2 line gets lower than the pump pressure (usually
only a few psi) then water will be pushed into the the CO2
line until it meets a blockage or more pressure.  If there
is no leak in your system, the water might only travel a
short distance because, with nowhere to go but to compress
within the CO2 line, the pressure will build until it is
just enough to stop the water.

A slow leak will eventually let more water pass.  A fast
leak will, well, let more water by faster.

A possible problem with a dump situation is that the CO2
tank will cool slightly due to rapidly escaping gas and the
fact that CO2 doesn't exactly follow the behavior of an
ideal gas (it's still a nice gas, even if it isn't ideal
;-)  ).  When the dump is done, the CO2 tank is warmed by
room temp, which can create a pressure drop, or
conceivably, a vacuum.  An unlikey situation if your
metering valve prevents a rapid dump into the tank and,
like TW, you don't get a blow-off through the safety valve.

All of this is attentuated by a decent metering valve
(okay, it doesn't have to be ametering valve per se, but
you still ought have a valve that meters the flow).

I think the situations where you actually get water all the
way back into your regulator or CO2 tank are, in practice,
very very rare.  I think check valves are like bubble
counters -- not essential but they can serve a good

I have a bubble counter and the check valve that is built
into it doesn't work (ha!).  So I have a separate check
valve added in-line.  That's on one setup.  On another I
have not check valve.  I split the risks ;-)

Scott H.