Molecular Vacuum Pump

Working principle
The pumping principle of turbomolecular pump is a kind of vacuum pump, which transfers momentum to gas molecule by high-speed rotating rotor to obtain directional velocity, and is compressed and driven to the exhaust port and then pumped out for the front stage. Molecular pumps should satisfy two necessary conditions for transporting gases:
1. Turbomolecular pumps must operate in the state of molecular flow. Because when the pressure of the gas contained in a certain volume of container is reduced, the average free path of the gas molecule increases accordingly. At atmospheric pressure, the average free path of air molecule is only 0.06 um, that is to say, as long as a gas molecule moves in space at 0.06 um, it may collide with the second gas molecule. At 1.3 pa, the average free path between molecules can reach 4.4 mm. If the average free path increases to a distance greater than the distance between the vessel walls, the chance of collision between gas molecules and vessel walls will be greater than that between gas molecules. In the range of molecular flow, the average free path length of gas molecules is much longer than the distance between the blades of molecular pump. When the vessel wall is composed of a stationary stator blade and a moving rotor blade, more gas molecules will be injected into the rotor and stator blade, laying the foundation for the formation of directional motion of gas molecules.
2. The rotor blade of the molecular pump must have a linear velocity similar to that of the gas molecule. It is only at such a high speed that the gas molecules collide with the moving blades and change the random scattering characteristics for directional motion. The higher the speed of the molecular pump is, the more advantageous it is to increase the pumping speed of the molecular pump. Practice shows that the higher the velocity of gas molecules with different molecular weights, the more difficult it is to pump them out. Molecular pump is a kind of vacuum pump which transfers momentum to gas molecule by high-speed rotating rotor to obtain directional velocity, and then is compressed and driven to the exhaust port and pumped out for the front stage. This kind of pump can be divided into:
1) The gas molecule of the traction molecular pump collides with the high-speed rotor to obtain momentum, which is driven to the outlet of the pump.
2) The turbomolecular pump is pumped by the combination of the rotating blade and the stationary blade at high speed. This kind of pump usually works in the state of molecular flow.
3) Compound molecular pump is a kind of compound molecular vacuum pump, which is composed of turbine and traction molecular pumps in series.