Three types of pump systems: positive displacement, momentum transfer, and entrapment.
Positive Displacement Pumps
Positive displacement: Uses 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
Momentum transfer: Uses high speed jets of dense fluid or high speed rotating blades to knock gas molecules out of the chamber.
Capture gases in a solid or adsorbed state.