I. Positive Displacement Vacuum Pumps (Most Commonly Used)

1. Rotary Vane Vacuum Pump (Most Common)

• Driven by a motor, an eccentric rotor rotates.
• Vanes on the rotor are thrown out by centrifugal force and fit tightly against the inner wall of the pump chamber.
• During rotation, the chamber volume on one side increases → gas suction.
• The chamber volume on the other side decreases → gas compression → gas exhaust.
• Through repeated cycles, gas is continuously removed from the vessel, and the pressure drops steadily.

2. Reciprocating Piston Vacuum Pump
   Similar to a piston engine:

• Piston moves downward → intake valve opens, drawing in gas.
• Piston moves upward → compresses gas, pushing open the exhaust valve for discharge.
• Continuous reciprocation achieves vacuum pumping.

3. Roots Vacuum Pump

• Two figure-8 shaped rotors rotate synchronously in opposite directions.
• The clearance between the rotors and the pump chamber is extremely small with no contact.
• During rotation, gas is forcibly “swept” from the inlet to the outlet.
• It does not achieve high vacuum on its own and is often used as a booster pump in conjunction with a backing pump.

II. Momentum Transfer Vacuum Pumps (For High Vacuum)

Diffusion Pump

• Pump fluid is heated to generate high-speed downward jets of oil vapor.
• Gas molecules collide with the high-speed oil vapor, gain momentum, and are carried toward the outlet.
• Oil vapor condenses and recirculates, while gas is removed by a backing pump.
• Capable of achieving high and ultra-high vacuum levels.

Turbomolecular Pump

• Equipped with high-speed rotating turbine blades.
• The linear velocity of the blades approaches the thermal motion velocity of gas molecules.
• Strikes gas molecules and transports them directionally.
• Clean and oil-free, widely used in precision instruments and semiconductor manufacturing.

III. Principles of Other Types

• Liquid Ring Vacuum Pump: An eccentric impeller rotates, forming a rotating liquid ring with water; gas is sucked in and exhausted via volume changes. Suitable for pumping gas containing water vapor and dust.
• Ejector Vacuum Pump: Uses high-speed fluid (water/steam) for entrainment to remove gas. Features a simple structure with no moving parts.
• Adsorption / Ion Pumps: Capture gas molecules using adsorbent materials or electric fields, used in ultra-high vacuum and miniature vacuum applications.