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Re: Needle valves in CO2 systems poll

1) Describe your CO2 setup.
DIY low-pressure system: 5lb tank, Cornelius (beer keg) regulator, Parker
(actually made by Porter before Parker bought them out) HR1 metering valve,
I.V. catheter bubble counter, various Swagelok fittings and tubing. The
system feeds into the intake of a Magnum 350 on a 45g tank. Gas is on
continuously and keeps pH around 6.8 (with a slight swing between day &
night).

2) What valve do you use (company name, part number, etc.)?
Parker HR1, an older model probably made in the early to mid '90s (model
2A-H1A-B-BK). Parker's data sheet states the maximum Cv of this valve is
0.0008. I posted info on this valve back when I first started using it...the
post is in the archives:

http://www.actwin.com/fish/aquatic-plants/month.9909/msg00549.html

(Parker has since redesigned the HR series. The newer HR0 is now the closest
in specs to my older HR1.)

3) How long have you been using this type of setup?
About a year and a half.

4) Have you experienced any problems with this setup?
Since it's a DIY system, it took a bit of effort to find all the components
and put it together. Personally, I liked the process. Once it was set up and
adjusted, the system runs with no problems: very little fluctuation, no
end-of-tank dumping, etc. The only problem I have experienced is when water
was sucked out of the tank into the CO2 air line. The rig is under the tank
and I do not use a check valve on the plastic line feeding into the Magnum
350 intake. Instead, I made a coil in the line above the water, which I
mistakenly presumed would prevent any siphoning of water from the tank. As
George Booth hypothesized (correctly I believe), when the CO2 tank runs out,
the CO2 gas left in the line is absorbed by the tank water, thereby
gradually reducing the volume of gas in the line. This creates negative
pressure and pulls the water into the line. The water made it to the Parker
valve before I caught it, but it had no apparent effect on the hardware.

5) If you could change something(s) about your current setup, what would it
be?
I eventually want to improve the plumbing hardware; I've got a mishmash of
stuff (copper pipe, part of a ss fuel line, etc. I hope to devise a way to
prevent water from flowing from the tank into the line if the gas runs out
(but without using a check valve). I'd also like to eventually get a better
regulator, and maybe add a graduated knob to the Parker.

6) What cV flow rates do you use?

Greater than zero but less than .00008. :D I don't know, really. The valve
is set to put out about thirty-five 3mm to 4mm diameter bubbles per minute
(0.5833333333 bubbles per second). As soon as Dave G. or someone else does
the math, I'll tell ya. ;)

Actually, I don't think Cv is very relevant in terms of measuring the output
of a CO2 system, if I understand the term correctly (volume of gas/liquid
flow at a given temperature relative to pressure drop across the valve).
What is relevant is the specific volume of gas injected into the tank. Since
a given Cv can pass more or less volume depending on various environmental
and system parameters, it isn't a very useful figure. Cv is more useful for
selecting the right valve for a given application. To illustrate this point,
consider that a DIY yeast bottle requires a different Cv (an open 1/8" tube,
essentially) than a CO2 tank regulated down to 25 psi (a 0.000002" orifice),
yet the actual output of the two systems can theoretically be identical.

Dan Dixon