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On Tue, 19 Sep 2000 "DaTrueDave" wrote:
> Ok, I've gone back and reread Dave Gomberg's coČ FAQ.  It does contain
> a lot of good information!  However, he mentions several times that a
> "low pressure" system isn't as stable as a "high pressure" system.
> I've been leaning towards wanting a low pressure system, but now I'm
> hesitant...   What kind of a difference in stability are we talking
> about?  I do realize that a good metering valve will cost a bit more
> than a "high pressure" reactor, but the difference in cost between
> those two items is the only difference in price, right?  And I thought
> that it was a Bad Thing© to run coČ through a regulator designed for
> another gas.
> Here's the section of the FAQ that confuses me:
> <<<What's the difference between high pressure and low pressure
> systems?
> A low pressure system runs about 1 psi, a high pressure system about
> 15 psi. A low pressure system is hard to regulate. The regulator will
> regulate well from about 10-25 psi. A low pressure system needs a way
> to drop the 10 psi to 1 psi. Ususally a needle valve is used, but this
> is not very reliable, since a needle valve is not designed to regulate
> pressure, but flow. If you set the regulator very low, the pressure
> will wander up and down. If you set the needle valve almost closed (as
> you must to make a big pressure drop) the flow rate will vary a lot.
> The right way to do low pressure is to daisy-chain a carbon dioxide
> regulator and a natural gas regulator. But that is expensive and
> untried "experimental" territory. If you must have a low pressure
> system it is the way to go. We can help with it. Bring your wallet or
> charge card, though. >>>
> ~~~~~~~~~~~~~~~~~~~~~
> Dave Engle
> Jacksonville, NC

Let me describe my low pressure system, which by the way, is so stable
that other than having the bottle filled every 9 months, I have never
touched it in 2 years.

I have a 5 lb. bottle with an ordinary beer tap regulator.  This
regulator had a shutoff valve on it, which I just left there, although I
really don't need it.  I then plumbed an oxygen regulator to the output
of the co2 regulator.  Next is a Nupro M needle valve and lastly, a 1
psi check valve.

The co2 regulator is set at 30 psi and the oxygen regulator is set about
5 psi.  With the co2 regulator alone I couldn't control the the output
pressure below 10 psi.

With the needle valve, I can control the output down to about 1
bubble/10 seconds, and this system DOES NOT dump when the bottle

In my opinion, a maintenance free system is worth spending a couple
extra bucks on.

Just my 2 1/2 cents worth.

Bob Ashcraft
Pittsburgh, PA