vacuumpressure

Vacuum pressure is the pressure within a closed system that is significantly lower than the surrounding atmospheric pressure. In technical contexts it is usually given as absolute pressure (P_abs), the pressure relative to a perfect vacuum. The term is distinct from gauge pressure, which is measured relative to ambient air.

Common units include pascals (Pa) in the SI system; torr (mmHg), bar, and atmospheres. One atmosphere equals 101,325 Pa. One torr equals 133.322 Pa; 1 bar equals 100,000 Pa. Vacuum levels are typically described by ranges such as rough, medium, high, and ultra-high vacuum, each spanning several orders of magnitude in P_abs.

Rough vacuum extends roughly from atmospheric pressure down to about 1 Torr (133 Pa). Medium vacuum covers roughly 1 Torr down to 10^-3 Torr. High vacuum ranges from about 10^-3 Torr to around 10^-9 Torr. Ultra-high vacuum is below about 10^-9 Torr.

Vacuum is produced using pumps and sealed chambers. Positive-displacement pumps can evacuate from atmospheric pressure to the mid range; turbomolecular and ion pumps provide high to ultra-high vacuum. Cryopumps and hybrid systems are also used. Proper system design includes minimizing leaks, bake-out to remove adsorbed gases, and using clean materials.

Pressure is measured with vacuum gauges chosen for the target range: Bourdon and Pirani gauges for rough to medium vacuum; cold cathode and ion gauges for high to ultra-high vacuum. Some gauges provide multiple readouts or require calibration; measurements are often expressed in Pa or Torr.

Vacuum pressure is critical in processes such as electron microscopy, surface science experiments, thin-film deposition, semiconductor manufacturing, vacuum distillation, vacuum packaging, and space simulation tests.