Vacuum is a volume of space that is empty of matter. In the context of laboratory and factory, it is usually a sealed volume with very low gas molecules count, i.e., its gaseous pressure is much less than atmospheric pressure. The first repeatable vacuum created in a laboratory is by Evangelista Torricelli in 1643. He built the first mercury barometer and wrote a convincing argument that the space at the top was a vacuum. Today, a vacuum pump is used to achieve the vacuum status of a sealed container.
Vacuum pumps can be categorized according to the technique used to achieve vacuum:
Positive displacement pumps repeatedly expand a cavity to allow gases to flow into the cavity from the sealed chamber. They then seal off the cavity and exhaust it to the atmosphere. Common positive displacement vacuum pumps include Rotary vane pump, Diaphragm pump, Liquid ring pump, Piston pump, Scroll pump, Screw pump, Wankel pump, External vane pump, Roots blower, Multistage Roots pump, Toepler pump, Lobe pump.
Momentum transfer pumps (molecular pumps) use high speed jets of dense fluid or high speed rotating blades to knock gas molecules out of the chamber. Common Momentum transfer pumps include Diffusion pump and Turbo-molecular pump
Entrapment pumps capture gases in a solid or adsorbed state. Common Entrapment pumps include Ion pump, Cryo-pump, Sorption pump,
Non-evaporative getter.
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