Pressure is the force applied perpendicularly on a unit area of a surface. There are three types of pressure as absolute pressure, gauge pressure and differential pressure. Absolute pressure is the measurement we take against a perfect vacuum, which uses an absolute scale. Gauge pressure is measured against ambient air pressure while differential pressure is the pressure between two points. We use different units for the measurement of these three types.
What is Bar?
Bar is the unit of measurement we use to measure absolute pressure. It is a metric unit of pressure, but it does not come under the SI unit system. One bar is exactly equal to 100,000 Pa (slightly lower than the atmospheric pressure at sea level). As a derivative, millibar is also in use as a common unit. Some other units derived from bar includes the followings:
Moreover, one bar is approximately equal to 0.987 atm, 14.50 psi (absolute) and 750.06 mmHg. Often, we give the atmospheric air pressure in millibars. Here, the standard atmospheric pressure at sea level is 1013.25 millibar. Furthermore, many engineers use the term bar rather than Pascal because, in Pascal unit system, we have to work with large numbers.
What is Barg?
Barg is the unit for the measurement of gauge pressure. Gauge pressure is measured against the ambient pressure. Therefore, it is equal to absolute pressure minus atmospheric pressure. Moreover, barg is the unit for the measurement of the pressure given by absolute pressure minus atmospheric pressure.
What is the Difference Between Bar and Barg?
Bar is the unit of measurement we use to measure absolute pressure while barg is the unit for the measurement of gauge pressure. So, this is the key difference between bar and barg. When we consider the relationship between absolute pressure, gauge pressure and atmospheric pressure, we can obtain absolute pressure by gauge pressure plus atmospheric pressure. However, for gauge pressure, it is absolute pressure minus atmospheric pressure. For example, the unit “bar” is useful when taking measurements in a vacuum while the unit “barg” is important when taking the measurements in the presence of atmospheric pressure.
Summary – Bar vs Barg
Bar is the unit of measurement we use to measure absolute pressure, while barg is the unit for the measurement of gauge pressure. Thus, this is the key difference between bar and barg.
1. “Pressure Measurement.” Wikipedia, Wikimedia Foundation, 12 June 2019, Available here.
1. “ReifendruckPruefen” By JEG14 – Own work (Public Domain) via Commons Wikimedia