PSIG Question
PSIG Question
(OP)
If a spec calls out for a leak test to be done at 5 PSIG,
should I add the 14.7 for atmospheric pressure (Gage reading = 19.7),
or does the PSIG imply that the 14.7 is included when the gage reads O (Gage reading = 5)?
should I add the 14.7 for atmospheric pressure (Gage reading = 19.7),
or does the PSIG imply that the 14.7 is included when the gage reads O (Gage reading = 5)?





RE: PSIG Question
The "g" means gage pressure.
The absolute pressure would be 5 psig + 14.7 (atmosphere, assuming you live near sea level) - 19.7 psia.
Does this answer your question?
RE: PSIG Question
What if I were not at sea level?
RE: PSIG Question
I'm not totally sure how those things are set up in regard to how far off they would be if you are at, say 9500' eelvation. Sure I can caclulate the atmospheric pressure at any elevation, but what I don't know is how the gauge will respond. I suspect if I buy a store-bought gage in Los Angeles and drive up to the summit of Mt Whitney (14,000'+) it won't be accurate, but I don't know by how much because I don't know how the mechanical Bourdon tube mechanism is calibrate dor set up. It might start rotating backwards.
If you need tight accuracy, or if you are at higher elevation, you will have to get a special gauge, one that can be recalibrated for the difference in atm pressure. If you look on the Ashcroft or Wika webpages you will find what you are looking for in the way of special gauges and how they are set up and calibrated. Don't call McJunkin or Kelly Pipe because they won't know.
RE: PSIG Question
Consider using lower case letters for the pressure units. Capital letters usually apply to proper names or large SI multipliers.
RE: PSIG Question
RE: PSIG Question
RE: PSIG Question
If that is so, then 5 psig is measured relative to whatever atmosphere/elevation you are operating in, whether at sea level, 14,000', or in outer space, and NOT relative to 14.696 psia. I still need to look it up to be sure though. Thanks! Pete
RE: PSIG Question
Near sea level, the affect of another thousand foot altitude is one-inch Hg or about a half psi. This may not be sufficiently precise for gauges in high mountain locations. BTW, the gauges that I buy have an accuracy near 0.5 percent. If you want something where the precision required is greater than about one psi then don't use a bourdon tube gauge.
RE: PSIG Question
A private airplane uses an aneroid barometer as the altimeter. Instruments on old private planes are usually called “steam gauges” in contrast to the glass panel or visual display based instruments. Pilot check navigation aids to obtain the current altimeter setting for that area (based upon the barometric pressure). This is done about every 100-mile.
I think that jets use aneroid barometer technology for their basic altimeter. Jets may also have a radar altimeter and a WAAS corrected GPS. The altimeter settings provide consistent adjustment with the steam gauges. Everything changes above 18,000 foot where everyone uses 29.92 as the altimeter setting.
RE: PSIG Question
Back to the OP's question, if the leak test is at 5 psig, then use a normal gauge and pressurize the system until the gauge reads "5". For some reason that is lost in the mists of time, PSV's, leak tests, and static tests are done at gauge pressure.
David Simpson, PE
MuleShoe Engineering
www.muleshoe-eng.com
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RE: PSIG Question