Question about vacuum and vacuum meter

[Micko]

I wonder why vacuum is sometimes measured in range from 0 to -1 bar. Is it because of it's measured relatively to normal atmospheric pressure?
I guess that normally, vacuum shoud be in range of 0 to 1 bar or something?
Can you help me understaning what terms "underpressure" and "overpressure" really means?
Thanks

 

[Ivan Seeking]

I wonder why vacuum is sometimes measured in range from 0 to -1 bar. Is it because of it's measured relatively to normal atmospheric pressure?

Yes, there is PSIG, or gauge pressure [or vacuum], and PSIA, or absolute pressure. Gauge pressure uses normal atmospheric pressure as zero. Absolute pressure is gauge pressure minus 1 bar. A measure of 0 PSIA [absolute] would be a complete vacuum.

I guess that normally, vacuum shoud be in range of 0 to 1 bar or something?
Can you help me understaning what terms "underpressure" and "overpressure" really means?
Thanks

Since you are starting with a gauge pressure of zero, which means that we are starting with atmospheric pressure [ 1 bar] as zero, anything lower than this would be negative, which is a vacuum.

Underpressure and Overpressure mean just what they say. If you have a system that operates between 1 and 2 bars, and you measure it operating at 3 bars, it would be 1 bar overpressure. If you measured it operating at 0.5 bars, it would be 0.5 bars underpressure.

 

[sir-pinski]

Yes, you are correct. Vacuum is often measured in the range of 0 to -1 bar because it is measured relative to normal atmospheric pressure. This means that at 0 bar, the pressure is equal to atmospheric pressure, and as the pressure decreases towards -1 bar, the pressure is considered to be in a state of vacuum.

The reason for this is because atmospheric pressure is typically the starting point for measuring pressure in most applications. So when we say something is at 0 bar, it means that the pressure is equal to the surrounding air pressure. As the pressure decreases below that, it is considered to be a vacuum.

As for your question about "underpressure" and "overpressure," these terms refer to when the pressure is below or above the normal atmospheric pressure, respectively. So when something is in a state of vacuum, it is considered to be underpressure, and when the pressure is higher than atmospheric pressure, it is considered to be overpressure.

I hope this helps clarify the terms for you. Let me know if you have any further questions.