What is Considered a High Vacuum?Īny negative pressure significantly below standard atmospheric pressure (760 Torr/mmHg, 29.9 inHg or 14.7 PSI) is considered a vacuum. A perfect vacuum (100%) as measured in all units including PSI, mmHg, Torr, mbar or inHg, is 0. A perfect vacuum is nevertheless an inevitable theoretical reference point that we, for example, use when determining and comparing percentages of vacuum. Outer space comes close with just a few hydrogen atoms per cubic meter, but it never reaches zero and the same is true even in the most technically advanced vacuum systems on Earth.Īlthough a small volume may contain no particles for a very brief moment, there would still be quantum phenomena such as photons. A perfect vacuum, which can also be referred to as full vacuum or absolute vacuum, would be a volume that contains no matter whatsoever. For example, a vacuum lifting system may operate at around 60% of a total vacuum. In the so-called rough vacuum range, from atmospheric pressure down to 25 Torr, it is also common (and more practical) to define vacuum as a percentage of a full vacuum. Pascal (as in kilopascal/kPa) is the metric standard unit for pressure and is normally the unit used in scientific and technical papers. Outside of North America, the more common units are negative millibar and/or kPa (often both are used on gauges). In North America, it’s common to use inHg in the rough vacuum range, Torr in higher vacuum ranges, and microns (thousands of a Torr) for pressures reached by backing pumps.
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