Question about vacuum and vacuum meter

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SUMMARY

This discussion clarifies the measurement of vacuum in relation to atmospheric pressure, specifically addressing the range from 0 to -1 bar. It distinguishes between PSIG (gauge pressure) and PSIA (absolute pressure), explaining that gauge pressure uses atmospheric pressure as a baseline. A complete vacuum is defined as 0 PSIA, while underpressure and overpressure are defined based on deviations from atmospheric pressure. The terms are illustrated with practical examples of pressure measurements in various systems.

PREREQUISITES
  • Understanding of PSIG (gauge pressure) and PSIA (absolute pressure)
  • Basic knowledge of atmospheric pressure and its role in pressure measurements
  • Familiarity with the concepts of underpressure and overpressure
  • Knowledge of pressure measurement units, specifically bar
NEXT STEPS
  • Research the differences between gauge pressure and absolute pressure in detail
  • Explore the applications of PSIG and PSIA in various engineering fields
  • Learn about pressure measurement techniques and instruments
  • Investigate the implications of underpressure and overpressure in system design
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Engineers, technicians, and students in fields related to fluid dynamics, pressure systems, and instrumentation who seek to understand pressure measurement concepts and their practical applications.

Micko
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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
 
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Micko said:
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.
 

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