What is "Relative Vacuum" and "Absolute Vacuum"

What Is Vacuum?

Vacuum theoretically means that the volume does not contain any substances. (There is no real vacuum in reality). Usually, the pressure in the container is lower than the normal atmospheric pressure (101325 Pa) is called a vacuum state.

The vacuum degree indicates the gas degree in a vacuum state, usually expressed in terms of pressure. In practical applications, vacuum degree is usually divided into absolute vacuum and relative vacuum.

Absolute vacuum is also called "absolute pressure", "ultimate vacuum". The values are all positive values. The smaller the number, the closer it is to absolute vacuum, that is, the higher the degree of vacuum. Usually absolute vacuums are suffixed with "abs.".

Vacuum degree from high to low:

2 mbar abs.> 100 mbar abs.> atm. (standard atmospheric pressure)


Relative vacuum is also called "relative pressure", "gauge pressure", "negative pressure". That is, the atmospheric pressure is used as the zero position, indicating how much pressure is lower than the atmospheric pressure. It is represented by a negative value. The larger the absolute value of this negative value is, the higher the vacuum degree is.

Relative vacuum is usually suffixed with "g".

Vacuum degree from high to low: -980 mbar g> -100 mbar g>atm. (standard atmospheric pressure)


Relative vacuum = absolute vacuum (absolute pressure) - atmospheric pressure

For example, the ultimate vacuum of a vacuum pump is 8 mbar abs., its relative vacuum is 8-1013 (standard atmosphere) = -1005.



The customer requires a vacuum of 0.08MPa, and the absolute vacuum of our vacuum pump is 160mbar. Can this vacuum pump be used?

Vacuum degree 0.08MPa is required, usually it means the dial pressure, that is the relative pressure. -0.08MPa g = -800mbar g. The absolute vacuum is -800+1013=213mbar. The absolute vacuum that the vacuum pump can achieve is 160mbar, which is higher than 213mbar, so it can meet the requirements.


If you want to learn more news about pumps and vacuum industry, please read these blog posts.


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