figured I would ask here...

is there a difference between PSI and PSIG??

 

i think PSI is straight pressure, where PSIG is absolute pressure minus atomospheric pressure, so when theres zero vacuum in the manifold it reads 0psig, thats my guess

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Eddiebx &raquo;</TD></TR><TR><TD CLASS="quote">i think PSI is straight pressure, where PSIG is absolute pressure minus atomospheric pressure, so when theres zero vacuum in the manifold it reads 0psig, thats my guess</TD></TR></TABLE>

thanks!

well... Im looking at small disposable co2 cartridges. They range from 12g co2 to 38 or so.

I used the Ideal Gas Law ( PV = nRT) to figure out pressure but my numbers dont match what I found on the safety specs on their website.

ill make sure all my units match and shat... anymore opinions?

 

psia=pounds per square inch absolute
psig=pounds per square inch gauge

in my work, absolute pressure refers to vacuum, or pressure below atmospheric pressure. Gauge pressure refers to pressure above atmospheric pressure, i.e. 0psig is 1bar, or normal ambient atmospheric pressure. 0 psia would mean a perfect vacuum, or absolute (such as in outer space). Generally speaking, you would use psia to measure pressure from perfect vacuum to atmospheric 0-14.7psia), and psig from atmospheric and above.

14.7 psia = 0 psig

I use different engineering units in my job as an automotive test engineer, it's a pet peave when people just say 'psi' without specifying psia, or psig.

psig=psia-14.7 at sea level

for all practical purposes, when we discuss boost, we always refer to psig.

Most people refer to millimeters of mercury, or millibar to measure pressures below 0 psig, or below 14.7 psia (vacuum), the old-schoolers use inches of mercury to measure vacuum.

the only catch to using psig gauges is that they are accurate only if atmospheric pressure is equal to the calibration pressure of the gauge.

If you wanted to be really ****, you could use an absolute pressure gauge(for a boost gauge) that would read higher than 14.7psia to read above atmospheric pressure, but it's probably not worth the hassle.

To replace a normal 30-30 gauge (30inhg-30psig) with an absolute pressure gauge, it would have to read 0-44.7psia...rather confusing...eh?

that's my .02




Modified by ForceFedDetroit at 9:53 AM 12/15/2004