The pressure in a fluid is defined as
"the normal force per unit area exerted on a imaginary or real plane surface in a fluid or a gas"
The equation for pressure can expressed as:
p = F / A (1)
where
p = pressure [lb/in2 (psi) or lb/ft2 (psf), N/m2 or kg/ms2 (Pa)]
F = force [1), N]
A = area [in2 or ft2, m2]
1) In the English Engineering System special care must be taken for the force unit. The basic unit for mass is the pound mass (lbm) and the unit for the force is the pound (lb) or pound force (lbf).
Absolute PressureThe absolute pressure - pa - is measured relative to the absolute zero pressure - the pressure that would occur at absolute vacuum. All calculation involving the gas laws requires pressure (and temperature) to be in absolute units. Gauge PressureA gauge is often used to measure the pressure difference between a system and the surrounding atmosphere. This pressure is often called the gauge pressure and can be expressed aspg = ps - pa (2)
where
pg = gauge pressure
ps = system pressure
pa = atmospheric pressure
Atmospheric PressureAtmospheric pressure is pressure in the surrounding air at - or "close" to - the surface of the earth. The atmospheric pressure vary with temperature and altitude above sea level.Standard Atmospheric Pressure (ATM) is used as a reference for gas densities and volumes. The Standard Atmospheric Pressure is defined at sea-level at 273oK (0oC) and is 1.01325 bar or 101325 Pa (absolute). The temperature of 293oK (20oC) is also used.
In imperial units the Standard Atmospheric Pressure is 14.696 psi.
A torr (torr) is named after Torricelli and is the pressure produced by a column of Mercury 1 mm high - equals to 1 / 760th of an atmosphere.
Pounds per square inch (psi) was common in U.K. but has now been replaced in almost every country except in the U.S. by the SI units. Since atmospheric pressure is 14.696 psi - a column of air on a area of one square inch area from the Earth's surface to the space - weights 14.696 pounds.
The bar (bar) is common in the industry. One bar is 100,000 Pa, and for most practical purposes can be approximated to one atmosphere even if
1 Bar = 0.9869 ATM
There are 1,000 millibar (mbar) in one bar, a unit common in meteorology.
1 millibar = 0.001 bar = 0.750 torr = 100 Pa
gauge
To convert from barG (gauge pressure) to barA (absolute pressure), you simply add atmospheric pressure to the gauge pressure. Assuming standard atmospheric pressure is around 1 bar, the conversion would be -0.02 barG + 1 bar = 0.98 barA.
Gauge pressure is what you get when you take the reading from your tire pressure gauge. Absolute pressure is the pressure inside your tires plus the atmospheric pressure, which is roughly; 14.7 psi, 101.3 kPa (kilo-Pascals), or one atmosphere. Absolute pressure measures all of the pressure on your tires, inside and out, whereas gauge simply measures the pressure inside the tire.
i need to explain what an absolute pressure gauge measures
The gauge pressure is the absolute pressure minus atmospheric pressure. If atmospheric pressure is considered to be 101 kPa, then the gauge pressure would be 219 kPa.
absolute pressure; gauge pressure; atmospheric pressure...
To convert between absolute pressure in kPa to gauge pressure in mm Hg, you can use the conversion factor of 1 kPa = 7.5 mm Hg. Therefore, if the required absolute pressure is 20 kPa, the corresponding gauge pressure would be 20 kPa * 7.5 mm Hg/kPa = 150 mm Hg.
if the gauge pressure is 206 kPa, absolute pressure is 307 kPa
If a gas has a gage pressure of 156 kPa its absolute pressure is approximately?
The gauge pressure is the difference between the absolute pressure and atmospheric pressure. If atmospheric pressure is approximately 101.3 kPa, then the gauge pressure would be 448.980 kPa (550.280 kPa - 101.3 kPa).
44.7 psi
The gauge pressure would be 448.955kPa.