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aturner0213
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Difference Between ATM (Gage) and PSIG

10/08/2014 9:34 PM

What is the difference between atm (gage) and psig? Are they the same, just written different? Or do they have different meanings? Thank for your help in advance!
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lyn
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#1

Re: Mechanical Engineering

10/08/2014 10:04 PM

Google will tell all.

atm=14.7PSI, the accumulated weight of all the air in a 1 square inch column of air from sea level to outer space.

Gauge is whatever it reads.

Do some research.
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SolarEagle
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#2

Re: Mechanical Engineering

10/08/2014 11:32 PM

pounds per square inch gage (psig)

atm = atmosphere (14.7 psi)

Then you have gage pressure vs absolute pressure...

Gage pressure usually starting at 1 atmosphere, and absolute pressure starting at - 1 atm or vacuum....

"It's just a matter of defining your 'zero point'.

In a real, actual gauge, pressure is measured relative to the atmospheric pressure. If there was 1 atmosphere of pressure inside a container (so it's the same pressure inside the container as it is outside it), the gauge will not read 1 atm, but rather 0 atm, as the pressure inside the container would just be the same as the pressure outside. Relative to the outside world there would be no pressure in the container. This is gauge pressure.

Absolute pressure is technically what we think of when we say pressure - the force that the gas is applying per unit area of the container.

If the gas is applying 101,300 Newtons per square meter, then the absolute pressure would be 101.3 kPa. On the other hand, the gauge pressure would be 0 kPa, as 101.3 kPa also happens to be the pressure of the atmosphere outside the container."

http://instrumentationportal.com/2011/instrument-basic-knowledge/theory/pressure-definition/

http://physics.stackexchange.com/questions/20460/gauge-pressure-vs-absolute-pressure

http://en.wikipedia.org/wiki/Pounds_per_square_inch

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Tornado
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#4
In reply to #2

Re: Mechanical Engineering

10/09/2014 4:07 AM

Good chart, but don't they say bard for differential pressure?

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SolarEagle
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#5
In reply to #4

Re: Mechanical Engineering

10/09/2014 10:05 AM

bard- stands for bar differential.....bara- bar absolute.....barg- bar gauge...bar=100,000 pascals(metric)....So under the heading "differential pressure" yes used properly...

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old salt
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#6
In reply to #5

Re: Mechanical Engineering

10/09/2014 11:12 PM

Yes, but wasn't Willie Shakespeare also the bard? One would think he would take preference over some silly thing about the weight of air from here to all the way up there. Everyone knows that the bathroom scale reads "0" when there is only air on it!

Good Luck, Old Salt

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JIMRAT
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#8
In reply to #2

Re: Mechanical Engineering

10/10/2014 9:44 PM

G'day S.E. I am reminded of a time in Oz when we were trying to be the 'science nation'. The new vacuum regulator gauges in our hospital were calibrated as pressure above zero in KPa, in keeping with your statement;- "Absolute pressure is technically what we think of when we say pressure - the force that the gas is applying per unit area of the container."

Sooo, on our new gauges 10 thingies was in fact high vacuum ( 10 KPa absolute ). The upshot was that when a doctor asked for low vacuum to drain a chest wound the patient ended up with a collapsed lung as the nurse ( or doctor ) would set the regulator to a low number. Common sense eventually prevailed and the intuitive way returned. That is to say that people think of vacuum as a real thing that can be measured in terms of small and big. Oddly we never say "in the partial vacuum on top of Mt Everest..." but we do say "in the partial vacuum outside the 'plane at this altitude" etc. We would say "in the reduced pressure on top of Mt Everest" but my vacuum cleaner has good vacuum not good pressure reduction.

Weird people!!

Jim

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Sheva
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#3

Re: Mechanical Engineering

10/09/2014 3:52 AM

psig is pounds per square inch 'gage' : [lb/in²] gage

Gauge (gage): Pressure reading relative to current atmospheric pressure ≈ 1 bar

Which mean : Absolute pressure = gauge pressure + atmospheric pressure. For example :

psi = psig + 14.69

14.7 psi = 1 atm

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dhayanandhan
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#7

Re: Difference Between ATM (Gage) and PSIG

10/10/2014 4:27 AM

Dear Mr.aturner021,

This topic was discussed few times in this Forum.

1. Pl. refer the Standard Text Book

2. Pl. open the following link (which is in this CR4 FORUM) AND YOU WILL FIND A PLENTY OF DATA.

http://cr4.globalspec.com/search/sitesearch?do=show&srchobjs=t%2Cc&order=asc&fs=14&sort=textmatchrank&query=GAUGE%20PRESSURE%20AND%20ABSOLUTE%20PRESSURE

DHAYANANDHAN.S
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James Stewart
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#9

Re: Difference Between ATM (Gage) and PSIG

10/14/2014 12:47 PM

psig = pound per square inch gauge pressure (relative to the outside ambient pressure).

psid - pounds per square in diffenential pressure (between two points in a "closed" system).

atm = a unit of pressure (not in standard use now) but used to be defined as average sea level pressure at a specified location at a specified temperature. Bar has replaced that measurement in most all standard usage. A gauge that reads in "atm" would read approximately the same in Bar.

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