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In article ,
says...

Eric R Snow wrote:

On Tue, 29 Nov 2005 21:46:53 GMT, "Leo Lichtman"
wrote:

"Grant Erwin" wrote: (clip) I'm running it 20 cubic feet per minute at 20
psi, (clip)
^^^^^^^^^^^^^^
The part I don't get is the "20 psi" part.

It doesn't matter. The psi. All that matters is flow per time. All the
pressure does is push the gas out through an orifice.
ERS

Actually, it may matter. The flowmeters are calibrated for one gas,
at one pressure. If this is a one-piece, non-adjustable TIG regulator,
the flowmeter is probably calibrated for Argon or CO2 at the regulator
pressure. In the most general case, flowmeters are calibrated at STP,
so if the system is at 20 PSI gauge pressure, that is 2.3 Atmospheres,
and so the flowmeter will read somewhat low.

If this is the usual rotameter (ball in a tapered tube
floweter), the accuracy will be affected by downstream
pressure, but is relatively insensitive to the regulator
setting. In other words, backpressure due to restrictions
between the flowmeter and atmosphere will affect accuracy
more than the pressure at the inlet to the needle valve,
which is upstream from the flowmeter.

Ned Simmons