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Needle valves in CO2 systems

I have heard many on this list claim great value for the use of a needle 
valve in a pressurized CO2 system.  Attempting to check it out, I was quite 

First some numbers:

Flow L/day               1     = 2.315E-05CFM
Input pressure, psi     30
Output pressure         15      15 delP
Specific Gravity         1.5       Re air=1.0, CO2=1.5
Temperature, F          70
Cv=     1.355E-06  =  0.0000013554

Now assuming we set the regulator for 30psi and want 15psi out of the 
valve, with a flow of one liter per day, we need a valve operating at a Cv 
of .000001

I have not yet found such a valve.  One writer suggested the ARO line, 
their smallest current valve is a 119-307-103 and the company's tech 
support waffles on the question of whether it will run all the way to shut 
off.  I bought one and tried it, it does nothing to stem the flow.   The Cv 
is way too large, it is intended for much larger flows.

Now maybe there is a valve that can be set to a Cv of .000001.   You should 
expect that its maximum Cv would be about .0001.  But I haven't found 
it.  Hoke does make a "micro-metering" valve, but it is very expensive.

Does anyone else have a proposed valve for use in this application?

Dave Gomberg, San Francisco            mailto:gomberg at wcf_com
NEW Planted Aquaria Magazine:        http://www.wcf.com/pam