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

["S. Hieber" <shieber at yahoo_com>]

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
purpose.

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.

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