TABLE OF CONTENTS Industry has grouped pressures below atmospheric level into [1]:
| Range of Pressure | |
|---|---|
| Rough vacuum | 760-1 torr |
| Medium vacuum | 1-0.001 torr |
| High vacuum | 0 001-10-7torr |
| Ultra-high vacuum | 10-7torr and below |
Rough vacuum is used in about 90% of the chemical, petrochemical, and other processing industries. This range generally includes vacuum distillation, filtration, crystallization, drying, reaction, and others. Medium vacuum is most applicable to molten metals degassing, molecules distillation, freeze drying, and others. High and ultra-high ranges are most useful for thin films, research, and space simulation.
For reference, note that the unit of vacuum measurement is torr.
| 1.00 torr | = 1mm mercury (mmHg), abs |
| 25.4torr | = 1 in. mercury (in. Hg) |
| 750.1 torr | = 1 bar |
| 1.868 torr | = 1 in. water at 4 C (in. H 2O) |
| 760 torr | = 1 standard atmosphere (atm) (at sea level) |
| Absolute pressure | = barometric pressure at location - vacuum |
Statements about vacuum can be misleading when a clarification is not included. Vacuum refers to the "degree of emptiness" of a process system. A perfect vacuum represents an absolute zero of pressure, which is technically unmaintainable. A vacuum system indicates a system that can be a matter of the degree to which the system approaches absolute zero pressure. To create a vacuum in a fixed system, it is necessary to draw out or pump out the air in the volume. When part of the air is removed, the system has a partial vacuum. For example, when a 15-in. Hg vacuum...
