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DaTrueDave at DaTrueDave at earthlink_net 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? 

Depends on the gear. Some of the cheaper needle valves are very suseptible
to thermal change. Any extraneous plumbing is too, so the choice of
materials here can make the system more or less subject to thermal effects:
big copper pipes are more suseptible than small stainless pipes. Also, the
flow rate (cV) of a given valve is a relative thing: the greater the input
pressure, the higher the flow, so gradual fluctuations after adjustment of
low pressure systems occur until things "settle in." Depending on the
injection method, changes in water depth can also affect the flow rate of
low pressure systems. Barometric pressure is also a factor (negligible,

That said, my own low pressure system has worked very well for a little over
a year now. It consists of a 5lb. tank, the same Cornelius regulator that
Dave G. sells, and a Parker HR-1 metering valve connected via some Swagelok
adapters and 1/4-inch stainless to 1/8-inch copper plumbing. The parker
feeds into an IV catheter inverted to serve as a bubble counter, and then
into the pickup of a Magnum 350. The system is on constantly, and pH levels
stay within a ±0.2 range with about 25 bpm (bubbles per minute). The HR-1
(HR stands for high resolution) has a 15-turn resolution with a Cv of .0008
at full open, and bubble-tight shut-off capability. I paid $45 for the
regulator, $50 for the metering valve, $60 for the tank, and about $15 for
miscellaneous hardware (Swagelok fittings and IV catheter were free,
compliments of my sister the vet and my friend the physicist, respectively).

I have never used Dave G.'s system, so I cannot justly compare it with mine,
but I respectfully disagree with Dave G.'s assertion that "The right way to
do low pressure is to daisy-chain a carbon dioxide regulator and a natural
gas regulator." There is no singular "right way."

Dan Dixon