# Re: Needle valves in CO2 systems

```Dave Gomberg at gomberg at wcf_com wrote:

> 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.
>
> 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=CFM/(22.7*sqrt((p1*delP)/((460+T)*sg)))
> 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.

Dave et al.,

Does anyone have the math skills to calculate what the cv is for a valve
that emits thirty-five bubbles per minute? Bubble size appears to be
approximately 3 to 4 millimeters. Input pressure is 25 psi. Temp at 75F.

This is what my Parker HR1 valve emits at about 3.5 turns open (15 turn
resolution. (I'm guessing the cv is magnitudes higher than 0.000001)

Dan Dixon

```