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Re: CO2 regulation

Wright Huntley sez:
> We are generally trying to reduce the liquified tank pressure to a
> manageable and safe level, and then we desire a constant volume/unit time
> (number of bubbles/sec). That's best done with a *flow* regulator, and not a
> pressure regulator. One time-honored way to get that flow regulation is with
> a good needle valve and a constant-pressure source.
> Turbulence in the flow through an orfice has long been used to control fluid
> flow rate, somewhat independent of input pressure. The non-linearity of the
> turbulence means the input pressure can change quite a lot for only a little
> change in the flow volume. The needle valve does that rather well, if the
> shape of the aperture is such as to be highly turbulent at the terribly low
> flow rates we demand. It helps to have sufficient pressure drop across the
> needle valve to be in that turbulent condition at all times. That is, run
> the input pressure up around 20 psi or more. It's easy to see why it can be
> quite thermally sensitive, too.

FINALLY! Someone understands that we are trying to regulate the flow
rather than the pressure.  If the CO2 control system fails due to the
normal increase in output pressure as the high side pressure drops, it
is a poorly designed system.  It doesn't matter how cheap nor expensive
the components are;  it either has to tolerate normal pressure
fluctuations or specify a multi-stage regulator so there will be no
significant pressure fluctuations.  

BTW, you can inexpensively achieve two-stage pressure regulation at a
very low output pressure by plumbing a low pressure LP gas regulator in
series with your tank regulator.  Your regulator probably has 1/4" pipe
threads in the body for its output, so you could connect the two
regulators in series with just a short pipe nipple.  The output pressure
will be low enough that just about any metering valve will be sufficient
to adjust the flow rate.  The potential problem here is that the
operating pressure might be too low (11" water column) to overcome the
head pressure in your tank to reach your reactor.