What is a Low, Medium, or High Vacuum?
Vacuums come in all shapes and sizes – and I am not referring to vacuum cleaners! Any local reduction in air pressure significantly below standard atmospheric pressure (760 mm of mercury, 14.7 pounds per square inch) is termed a vacuum (except by your local weather person who talks about ‘low pressure areas’). For convenience (and because there must have been a meeting of elder statesman with nothing better to do), the Torr in honor of some Italian named Torrecelli is used to designate a pressure of 1 mm of mercury I guess referring to ‘Torrecellis’ all the time would be too confusing. 🙂 The Vacuum Chart provides a nice instant summary of pump types, gauges, and applications, as a function of the level of vacuum. The following dividing lines between low, medium, high, and ultra-high vacuums are somewhat arbitrary but will be convenient for discussion: • Biosphere: 1 atm (760 Torr) to .5 atm. At sea level, the average pressure is about 1 atm. The weather person will talk about ‘inches
