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Re:Beginner's lessons - Misguided Thinking
> To: Aquatic-Plants at actwin_com
> Subject: Re:Beginner's lessons - Misguided Thinking
> From: Dave Gomberg <gomberg at wcf_com>
> Date: Fri, 24 May 2002 15:05:15 -0700
> At 03:48 PM 5/24/02 -0400, Tom Wood asked:
> >So, are you still insisting that "the real way a needle valve works" is only
> >when the gas running through it reaches the speed of sound?
> 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.
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 signifacant 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
IIRC from when I read up on this last year, needle valves are
constructed with valve seats that encourage or even maximize
turbulance. So the work is already done for us by the valve makers, and
we don't really need to understand the science.
But Tom's outburst was still uncalled for.