View Full Version : What's the 'G' in PSIG?

01-16-2005, 12:12 PM
At times I see pressure referenced as PSIG, e.g. in a Victor welding/brazing booklet. What's that G? Is that simply meaning the gage pressure?

01-16-2005, 12:35 PM
No, don't think it has anything to do with that. After a simple Google search I come up with Pipeline Simulation Interest Group (PSIG) so I am SURE that is what it means. http://bbs.homeshopmachinist.net//biggrin.gif

PSIG: Pounds Per Square Inch Gauge meaning measured at the gauge but I have seen it used in reference where there was no gauge so the term can be used as needed apparently.

[This message has been edited by JRouche (edited 01-16-2005).]

Stu Miller
01-16-2005, 12:38 PM

It stands for "gage", meaning the pressure is referenced to atmospheric pressure. That is, gage pressure is the pressure above atmospheric.

The alternative is psia, meaning absolute pressure, that is referenced to a hard vacuum, 0 psia

Stu Miller

01-16-2005, 12:40 PM
It means gauge pressure as opposed to absolute pressure, which adds atmospheric pressure.

30 PSIG = 41.7 PSIA assuming absolute pressure is 14.7 PSI at place & time of measurement.

[This message has been edited by JCHannum (edited 01-16-2005).]

Dave Opincarne
01-16-2005, 12:40 PM
IIRC its "Gas" as in preasure exerted my a gasious medeum as opposed to solid. But this is from memory and I haven't had coffee yet so YMMV.

01-16-2005, 02:40 PM
Oh, yeah, after reading Stu's and JC's responses I now remember it. In fact I think I asked this same question 3 or 4 years ago on this BB.

That's the wonderful thing about getting older. You get to learn the same things over and over. http://bbs.homeshopmachinist.net//biggrin.gif (Embarrassing nevertheless!)

Thanks guys.

01-16-2005, 10:25 PM
Guage is correct. A guage has a flex tube inside it with a known resistance, as the curved tube flexes the geared guage rotates. Guage pressure is calculated against a known resistance, the tube.

Differential pressure?, is dependent upon atmospheric pressure at the moment. It uses the atmosphere to recalibrate. Actually two sensors with one correcting the other.

Then inches Water column pressure, inches Mercury, both common measurement techniques in instrumentation. Just another way to measure pressure in different formats.

01-16-2005, 11:38 PM
lynnl, we can wrap our own presents too, and still be surprised...


01-17-2005, 12:58 AM
<font face="Verdana, Arial" size="2"> A guage has a flex tube inside it with a known resistance</font>

It's called a Bourdon tube.

here (http://www.tpub.com/content/fc/14104/css/14104_232.htm)

Herb Helbig
01-17-2005, 01:02 AM
lynnl - we keep meeting nice new people all the time, too!


01-17-2005, 10:46 AM
That's right. And they have a lot in common with our old friends too.

Watching movies and reading mystery novels is another area where being old offers some pluses. If it's been more'n 6 months since I saw a movie, then seeing it again is a brand new experience.

01-17-2005, 12:37 PM
Evan: as opposed to the Piton tube inside a instrument valve? (air flow speed) Or airplane?

Ha.. too much information for someone else who does not need too many confusions..

When water goes through them Bourdon tubes inside a old timey air controlled 3/15 PID steam loop controller (actually pd loop) you have to recalibrate, the weight of the water actually slightly distorts the tube.

What got me was the micro-motion series of flow loop meters.. it had a twisted loop of stainless tubing that they actually imparted a vibration of a known frequency into, they had pickoff coils on both sides that measured the "twist straightening" effect and the angular distortion of the tube and the dampened frequency difference. I sat in a motel room unable to sleep with all the knowledge creeping into my brain from the manuals. Gee.. then the coriliss D loop meter came out, seems it also pulsated but using another type of loop distortion method.

Air, it's one hard thing to measure linearly. We had hot-wire temperature transmittal meters, flapper wheel turbine meters, and tube pressure / orifice differential = flow. None were linear outside a given narrow range. I was building machines to make "foam" to blow a scotchgard carrier through the textile fabrics.

I spent days in motel rooms. (traveling technician) Knowing if I went drinking in a strange town it'd end badly, nothing to read but manuals. Then I got snowed in North Western Tennessee for two weeks with only one movie to watch, Jerimiah Johnson "Mountain man". I could mouth each word by each character in the movie. See how I ended up "this away?"

Then I started putting my Harley up into the service van, sitting it into the motel room with a cookie sheet under the engine to catch the drips.. cleaning, polishing each stainless bolt by hand. dreaming of what insane thing I would do to it next.

The company thought I was having too much fun, so they put me over the shop fabrication. And you know with my "type A" personality that didn't end well.

I got some of the best instrumentation training manuals available... DUpont factory, Micro-motion, rosemont.. the Dupont is the best.(made to train farmers how to work on instruments). if someone would convert them to pdf and post them it'd sure help society in general become more educated.

Gee, I'm bored, going to the shop.. Work off the next project I drawed up a trace-flamecutter last night.. NO computer just a plywood pattern. I smoked my shop up with the cutting torch hooked to my cnc machine on a long arm.