A vacuum device or a vacuum pump is a device that removes gas molecules from a sealed volume in order to leave behind a partial vacuum.
Vacuum devices can be broadly categorized according to three techniques:
- Positive displacement pumps use a mechanism to repeatedly expand a cavity, allow gases to flow in from the chamber, seal off the cavity, and exhaust it to the atmosphere.
- Momentum transfer pumps, also called molecular pumps, use high speed jets of dense fluid or high speed rotating blades to knock gas molecules out of the chamber.
- Entrapment pumps capture gases in a solid or adsorbed state. This includes cryopumps, getters, and ion pumps.
- Others such as Venturi vacuum pumps and Steam ejectors