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Re: Avoiding Dumping CO2

> Date: Thu, 23 May 2002 07:07:49 -0500
> From: "Tom Wood" <tomwood2 at flash_net>
> Subject: Re: Avoiding Dumping CO2
> Announcement: Lithium is no longer available on credit.
> "The real way that needle valves work is by running "sonic", which refers to
> the fact that the gas in the most tightly constricted part of the valve
> reaches the speed of sound."
> Uh huh. What planet are we channeling from today Dr. Lizardo? At 21 degrees
> C (70F), sound travels at 344 meters per second. Is there some kind of new
> physical property that we haven't heard of that comes into play when a gas
> is moving that fast? Is this some kind of 'Back to the Future' thing?
> "That is very hard to do with the very low flow rates we use, which explains
> why only very fine valves do a good job of it. The best is likely the Hoke
> at $130-200 (micrometering valve).   The next best I have found is the Fabco
> NV-55 which you can get from your local pneumatics dealer or from me.  It is
> closer to $25-30.  It is a much better deal than the Hoke but not as good a
> valve.   To ensure sonic flow in either valve, you need the pressure drop to
> be about 50% of absolute pressure."
> Um, what is "absolute pressure" and why is 50% of that important? A needle
> valve works by moving a tapered stem (a needle) in and out of a
> correspondingly tapered shaft with openings for the gas at either end. Think
> of it as robot sex.....or don't. Anyway, the better valves are machined so
> that the parts fit nicely and so that the relatively crude movements of a
> human hand produce finer movements within the valve. Screw the stem all the
> way into the shaft and there is no path for the gas. Back it off a little
> and the gas has room to move around the needle to the other end of the shaft
> where there is an outlet port. The speed at which the gas does this is
> irrelevant.
> "If your output from the needle valve is a couple of psi, this means an
> input gauge pressure of about 20psi to be safe.   Less and your valve will
> not be running sonic (possibly) and it may not be providing the protection
> you are hoping for."
> Well this is pure nonsense. Protection from what? Sonic boomlets?
> "Please ask about anything I did not explain well."
> Please tell us more about this alternate universe you inhabit.

I just love it when someone decides to show off their ignorance by
ridiculing something they don't understand.  It elevates the ignorance
(which is excusable) to arrogant stupidity (which is not).

Best regards,