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Re: co2 metering valves (alternative to regulator)

"toan" <zzttzz at hotmail_com> sez:

> Maybe this little tid-bit would be useful for those who are looking into 
> compressed co2 but dont have the wallet for it.
> the cost for 2.5 lbs bottle and valve was around $30--you may pay a little 
> more depending. I bought a new Aluminium bottle for $20 at parsons airgas in 
> San Diego (on sale) and bought a 5000 psig "Parker" metering valve locally. 
> Connected it to the bottle directly and skipped the regulator altogether. I 
> recall reading someone else's experience with the same "experiment" which 
> prompted me to give it a try.
> Well, it works great and nothing blew up. very consistent airflow. less 
> valves and connections to worry about. Only problem is that initial setting 
> is difficult but after you set it once, you just leave it there. I have it 
> in a room where temperature flux is pretty drastic but the effects of 
> thermal expansion is negligible on this valve. has been consistently putting 
> out a bubble every 2 seconds.
> I should warn that not every metering valve is adequate for handling liquid 
> co2, the one I bought specifically says 5000 psig on it (what does the g in 
> psig stand for anyway?) and i think compressed co2 is 2000 or 3000 lbs. 

It's probably a real nightmare to get it adjusted, cuz the valve is
dropping at least 700 psi.  But you only have to do that once.  The
danger I see here is the connection from the CO2 tank valve to the
metering valve.  If you can screw a CGA 320 fitting into the needle
valve block, or use high pressure steel lines with appropriate fittings,
there should be no problem.  The CO2 pressure will not vary much, as it
is being regulated by the vapor pressure of the liquid in the tank. 
Everything should be pressure rated at least 1800 psi, although the
working pressure is likely to be about half that.

BTW, "psig" refers to the pounds per square inch from the guage's
perspective.  It is the absolute pressure (psia) minus the atmospheric
pressure (about 14.7 psi).  Don't worry about it.