Pumping principle of turbo molecular pump

Turbo molecular pumps must work in molecular flow. Because when the pressure of the gas contained in a certain volume vessel is reduced, the mean free path of the gas molecule increases accordingly.

At atmospheric pressure, the average free path of the air molecule is only 0.06 micron, which means that a gas molecule may collide with the second gas molecule as long as it moves in space at 0.06 micron. At 1.3Pa, the mean free path between molecules can reach 4.4mm. If the mean free path is larger than the distance between the vessel walls, the collision probability between the gas molecules and the vessel walls will be greater than that between the gas molecules.vacuum-pump-oil

In the range of molecular flow, the average free path length of gas molecules is much longer than the distance between the blades of the molecular pump. When the wall is composed of a stationary stator blade and a moving rotor blade, more gas molecules will be injected into the rotor and stator blades, laying the foundation for the formation of the directional movement of gas molecules.