How do vacuum pumps remove gas from below atmospheric pressure?

Vacuum pumps function as compressors that intake gas at pressures below atmospheric pressure, compress that gas, and discharge it at atmospheric pressure. Because gas occupies a much larger volume at low pressures, these pumps are often bulky.1

Various mechanisms are used to achieve this:

• Mechanical Compression: Devices such as reciprocating piston and rotary-vane pumps physically move and compress gas to exhaust it from an enclosed space.12
• Jet Ejectors: Steam jet ejectors use high-velocity steam to transfer momentum to the gas, which is then compressed through a diffuser.1
• Cryopumping: Cryopumps utilize extremely low temperatures—often using helium—to condense gases onto a cold surface, effectively removing them from the system.3

Because mechanical pumps can be limited by internal leakage or oil-related factors, they are often used in conjunction with other specialized pumping systems to reach the desired vacuum levels.2