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Re: "G" in PSIG

In a message dated 3/27/00 3:54:21 AM Eastern Standard Time,Toan  writes:

<<  I should warn that not every metering valve is adequate for handling 
 co2, the one I bought specifically says 5000 psig on it (what does the g in 
 psig stand for anyway?)   >>

Since the many on this list who could respond to this more authoritatively 
than I, chose not to, here goes. As I recall from my automotive tech school, 
the "g" stands for "gauge", as opposed to psia, where "a" stands for 
"atmosphere.  The difference is in calibration.  Psig gauges read zero psi at 
rest, thus not taking into account atmospheric pressure of around 14.7 psi.  
A psia gauge will read 14.7 pounds of pressure at rest at sea level.  The 
automotive trade and I suspect most non-scientific uses use psig.  I would be 
interested in knowing who uses psia gauges and why, but those responses are 
probably more appropriate off list.
    Pierre Gagne
    Kensington, MD