"What the hell is Mr. Wood's problem?"
I just don't like seeing misinformation constantly repeated.
Regarding the sonic nonsense. We don't use needle valves in a way that
any of that applies. Sonic flow, Cv and all that applies when the
valve is under relatively high pressure on the inlet side and is
moving a lot of gas at a relatively high rate of flow measured in lots
of cubic feet per minute (CFM) against a given head pressure. At best
we are moving a fraction of a cubic foot per -hour- with relatively
low pressures on both sides of the valve.
We use the valves in an 'almost closed' position. We use needle valves
because they have tiny parts with tiny threads that can create what is
best described as a tiny leak. A small thread pitch coupled with a
finely tapered needle and seat provide a higher degree of control over
the leak through the valve. The bubble of CO2 gas ooches* around the
needle and into the outlet hole on the other side of the chamber. It
doesn't matter how fast it does that because it is laminar flow anyway
at the tiny rate of flow we are using.
It doesn't even have to be a 'needle' valve. We could use any type of
valve, including any clunky hardware store valve, if they had fine
enough threads and seats to create small movements and pathways. But
they don't so we use needle valves to get that small movement with our
big clumsy fingers.
When used in the 'almost closed' position the way we use them, needle
valves have the additional benefit of creating back-pressure on the
regulator. Which keeps the regulator from over-reacting to the effects
of a CO2 cylinder that is running empty. Without that back-pressure,
the mechanism in a single stage regulator interprets the dropping
pressure on its inlet side as a higher demand on its outlet side, and
it opens up, thus creating the fabled end of tank dump. Add an 'almost
closed' valve to create some back-pressure, and there is no dump. > Ever.
TW
* The Ooch is a unit of measure named after Beatrice Ophelia Ooch, who
with her husband Horatio Octavius Ooch, died tragically while
performing an experiment involving seven chickens and a garden hose.
They were buried side by side with only their initials on the
headstones: B.O.O. H.O.O.
_______________________________________________
Aquatic-Plants mailing list
Aquatic-Plants at actwin_com
http://www.actwin.com/mailman/listinfo/aquatic-plants