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The Emperor's New Clothes
> Let's be clear here. You can use a needle valve in your setup and reach
end of cylinder and run right thru all the gas and kill all your fish if
the valve is not running sonic or even close. A valve (without further
specification) doesn't prevent anything. If the valve is running sonic, the
severity of a dump is reduced. For the reasons cited previously by several
other posters. So if the needle valve is to WORK (reduce a dump) it must
be running sonic (or on the verge of sonic). And that does mean that in the
most constricted part the speed of sound is reached. If you have any
further questions about this talk to Parker Hannefin. I hope I have made
this simple enough for you.<
Okay, I did. But seeing as how it's a holiday weekend we may not hear back
from Parker Hannefin for a few days. In any case, one of our resident
engineers weighed in:
"Actually, you have oversimplified it, or used the wrong terminology, or
something. The important thing is to have a flow restrictor (such as a
needle valve) with a significant pressure drop across it. You can operate
the valve in its linear range if you want and it will still provide
significant protection. If you set the valve up for turbulent flow (but
still subsonic), it will provide better regulation. If you set the valve so
that it is fully choked, it will provide maximum flow regulation."
But Tom's outburst was still uncalled for."
Excuse me? I get called arrogantly stupid for pointing out the obvious, but
you let the above nonsense slip by like that?
I was willing to modify my statement about the irrelevancy of gas speed to:
The speed at which the gas does this is
irrelevant *under the conditions that most aquarium systems operate.* But
now you say that the valves will work at linear, turbulent and choked flows.
A painfully simple experiment disproves everything Dave has asserted. Set
your regulator to 20 psi and your bubble rate to, say, 2 bubbles per second.
Now, leave the needle valve alone and increase the pressure from the
regulator until the bubble rate no longer increases. Got it? The valve is
now running "sonic", aka choked. Or at least close to it. (My regulator
control knob bottomed out at about 120 psi, so the choke point is even
higher.) If the valve is *now* running sonic, what was it before when it was
operating perfectly at 20 psi? Turbulent perhaps?
The assertion that a valve has no value in controlling a cylinder dump is
simply astonishing. Anyone else care to comment on that while we wait for
And finally, I am not the one taking the condescending attitude toward
anyone that points out that the emperor is naked.
Like: Beginner's Questions
And: But to summarize it simply (so you can understand it)
And: I hope I have made this simple enough for you.
This list is about truth, justice, freedom and the American.....uh, well,
never mind that....I think that erroneous assertions deserve some amount of
ridicule. I think Dave's assertions are flat out wrong. I don't think it is
wrong of me to point that out in a way that is a little humorous. I laughed
at the sonic boomlets too when I saw it posted.