Lowest negative pressure (vacuum) 2

[boboG]

Hi folks, can someone please help me with negative (gauge) pressure scales and vacuum? I know -1 bar gauge is 1 bar below atmospheric -vacuum (or almost) but does it make sense to say that a pressure gauge is ranged from 0 to (minus 2.5 barg)? If so what does this mean?

 

[25362]

http://www.engineeringtoolbox.com/pressure-d_587.html

 

[boboG]

thanks 25362, I get the idea but I still can't figure out what (minus 2 bar-gauge) means!!

 

[epoisses]

-1 barg = 0 bara, or an absolute vacuum (which does not exist but is at least meaningful)

-2 barg does not exist and is meaningful... unless you'd be using antimatter..?

 

[epoisses]

-1 barg = 0 bara, or an absolute vacuum (which does not exist but is at least meaningful)

-2 barg does not exist and is meaningless... unless you'd be using antimatter..?

 

[Compositepro]

A pressure gage that reads "gage pressure" is actually measuring the difference in pressure between the pressure sensing connection and the pressure outside the case of the gage. If a pressure gage mounted to a sealed tank reads zero and then the tank is submerged in 30 feet of water it would read minus 15 psig (or 15 psi of vacuum). People get confused thinking of vacuum because vacuum doesn't really exist. Think in terms of absolute pressure and everything makes sense.

 

[JStephen]

IE, a pressure gauge could be rated to -2.5 atmospheres. In normal applications, it would never see this- but could if it was in a pressurized container or submerged.

 

[25362]

For liquids under metastable conditions, one hears of negative pressures as in:

http://www.aip.org/pt/feb00/maris.htm

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

 

[sailoday28]

To add to comments of 25362 (Chemical),==normal fluid pressures, which are positive represent compression. A fluid exhibiting negative pressure is in tension.
Regards

 

[25362]

Allow me a digression in a parallel line of thought, there was once a discussion on pH, whether it could be outside the range 0 to 14. The answer to this issue is yes, pH values could be outside the 0-14 range which, BTW, is based on the Lowry-Br[ø]nsted model and at room temperature.