Thanks, but...


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Posted by roakey on March 01, 2002 at 20:47:48:

In Reply to: Re: Well, yhea, but.... posted by Kendall Raine on March 01, 2002 at 15:09:58:

I thought it was a joke, but I wasn't sure, thanks...

Ok, this still doesn't sound right. I'm not trying to argue, but I'm explaining what I don't understand.

>>By lowering the flow, you lower the rate at which gas escapes from the cylinder.

But you don’t lower the flow. When I brethe in I move X number of molecules from the cylinder into my lungs, it doesn’t matter if the IP is at 90 or 180, or, for that matter if it’s one of the old single-stage double hose regulators. I move X number of molecules through the regulator, no matter what; it’s my lung capacity and breathing rate that determines that, not the IP. Another way of putting it is that if I breathe down an AL80 in 60 minutes with a normal IP, I’ll STILL breathe down an AL80 in 60 minutes with a lowered IP. So lowering the IP does not “lower the rate at which gas escapes from the cylinder.”

>>This in turn lowers the rate of expansion which lowers the cooling effect which is a cause of first stage freeze-up.

But by lowering the IP you INCREASE the expansion going on in the first stage. You’re going from tank pressure to an intermediate pressure. Lowering the intermediate pressure means that the gas is expanding more, not less. This is why I stated that it would appear that lowering the IP increases, not decreases the probability of a first stage freeze-up.

>>The lower the IP, the lower the number of molecules flowing through the orafice per unit of time.

Simplifying somewhat, the only time gas is flowing through the orifice is when you’re breathing. Your lung volume does not vary with IP, so the same number of molecules flow through the orifice during a breath no matter what the IP is.

Where’s my disconnect?

Roak


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