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Re: Needle valves in CO2 systems

> Date: Tue, 02 Jan 2001 07:24:01 -0800
> From: Dave Gomberg <gomberg at wcf_com>
> 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 
> disappointed.

As I've mentioned before, I use a homemade equivalent of a capillary
tube to restrict the CO2 flow.  I adjust the flow rate by varying the
output pressure of the CO2 regulator.  I don't know what its Cv is,
but the flow rate is extremely nonlinear (in a good way).  I normally
operate the regulator at about 3 psig, but to double the flow rate, I
might have to increase it to 10 psig, and to double it again I might
have to go to 40 psig.  The cross sectional area of the tube is
non-uniform.  I suspect that at its most restrictive point, the gas
velocity is approaching the speed of sound (thus establishing a
maximum flow rate at any pressure).

It's a very low-tech approach to rocket science ;-)

Best regards,