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Re: [APD] empty CO2 cylinder -- tests, acid, and valves

You're lucky about dumping.  Many others have not been so
lucky. You're unlucky about the cost of retesting.

If you're doing tank exchanges, you should never pay for
the retesting and stamping the tank ;-) .

If one hase one's own tank, the cost can vary. It's a
little less than $15 in these parts for a tank that holds
ten-pounds of CO2.  Retesting is required in the US every
five years under DOT regulations.

When CO2 dissolves in water some it forms a parigmatically
mild acid called carbonic acid (H2CO3). It exists in an
equilibrium with water when the CO2 is dissolved in water.
It is not possible to obtain pure carbonic acid. 

Any acid on metal can corrode, but I wouldn't call a small
amount of carbonic acid, in solution, "highly corrosive."
Possibly the worst thing about getting water and carbonic
acid in your CO2 tank is not that it's a strong acid but
that it's hard to get out and therefore likely to remain
for a long time.  You pretty much need to remove the main
valve on the CO2 tank to get water out.

Open and shut?  Viscosity might matter but I wonder if a
valve of any kind that is not closed would stop rather than
merely slow the passage of water. A good quality check
valve might be a better idea -- any force that would draw
water towards the CO2 tank would force the check valve
closed, blocking the water flow.

Scott H.

--- Steve Pushak <teban at powersonic_bc.ca> wrote:
> I've never seen the so-called end of tank dump occur &
> I've gone through
> several tanks in the past. Much more likely to occur is
> that when the CO2
> flow rate stops, the CO2 in the lines is dissolved into
> water. The water
> travels back up the lines into the needle valve &
> potentially into the
> regulator & cylinder. Fortunately, I believe the needle
> valve prevents most
> of the water from passing backward. Water & CO2 in the
> regulator or cylinder
> would be highly corrosive. I disconnect the lines as soon
> as I see the
> cylinder pressure drop or notice water going back up the
> lines. Then its
> time to refill the cylinder. Keep track of the
> certification date on the
> cylinder because you might get stuck with the cost of
> hydraulic testing for
> recertification at about $60. Its more economical to
> bring the tank in
> before it gets empty & exchange it with a full one.
> Take what you read here on the APD with a large grain of
> salt. There is
> considerable difference of opinion on certain subjects.
> It's better when
> those differences are discussed. It seems as if many of
> the old "experts"
> aren't posting very often any more.
> Steve P
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> Aquatic-Plants at actwin_com
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