Pressure

Pressure
The pressure of a gas on a boundary surface equals to the  force exerted by the  gas on an area of a real surface divided by that area. For example a gas or a liquid in a container forces a pressure perpendiculary to the container walls; same proceeds from a firm body on its surface.

Pressure units
Nowadays the legal pressure units are Pascal as the SI unit, abbreviation Pa, and bar as a special unit designation.

p = F/A 

1 bar=1000 mbar=10-5  N⁄m2 = 105 Pa.The unit commonly used in vacuum technology is the mbar.

Pressures and their translation
PascalmbarTorrpsi
Pa10,01

0,00750065

0,00014504
kPa1.00010
7,500650,14504
Mpa1.000.00010.0007.500,65
145,04
bar100.0001.000

750,06

14,5032
mbar10010,75006
0,0145032
Torr133,3221,33310,01934
psi6.894,868,9551,7151

 

Definitions and Units

Absolute pressure
In vacuum engineering the absolute pressure is standard, what means the pressure measured in relation to the absolute vacuum.

Ambient pressure
The ambient pressure p_amb is the atmospheric pressure on the Earth´s surface.

Normal pressure
The normal pressure is according to DIN 1343 p_n = 1013,25 mbar.
The normal temperature ist T_n = 0°C = 273,15 Kelvin

Normal conditions refer to the established standard temperature T_n and standard pressure p_n of a solid, liquid or gaseous substance.

Gauge pressure
In technology and everyday life relative pressure is used, i.e. the pressure in relation to the current ambient pressure p_amb.