Low vacuum (1013 to 1 mbar), also called rough vacuum or coarse vacuum, represents pressures 760 to 25 Torr. Flow in this range is viscous, as represented by most common fluids. Mechanical vacuum pumps are used for low vacuum, and represent the large majority of pumps in industrial practice.
Medium vacuum (1 to 10-3 mbar) represents pressures between 25 to 10-3 Torr. This is a transition range between viscous and molecular flow. Most pumps serving this range are also mechanical.
High vacuum (< 10-3 mbar) represents pressures between 10-3 to 10-9 Torr absolute. Flow in this region is molecular or Newtonian, with very little interaction between individual molecules. A number of specialized industrial applications, such as ion implantation in the semiconductor industry, fall in this range. Non-mechanical ejector or cryogenic pumps are usually used.
Ultra high vacuum (< 10-7 mbar) represents absolute pressures below 10-9 Torr. This is primarily for laboratory applications and space simulation. Keep in mind that a "perfect" vacuum-that is, a space with no molecules or atoms-is a purely theoretical condition. Only in interstellar space is this condition approached at all closely, and even there a few atoms per cubic meter will be found. In practice, all vacuums are partial.
|
Torr (mmHg)
|
mbar (10-"MPa)
|
psi
|
Inch Hg
|
atm
|
pa
|
|
1
|
1.33
|
0.01934
|
0.03937
|
0.00132
|
133.322
|
1 atm = 14.70 psi
1 bar= 14.50 psi
1 MPa=145 psi
1 in. Hg = 0.4912 psi
1 in. H20 = 0.0361 psi
1 torr = 0.01934 psi
1 Micron = 1.970 x 10-5
