Principles of Operation

The turbomolecular pump is a bladed turbine that compresses gases. By the momentum transfer from the rapidly rotating rotor blades to the gas molecules the non-directed thermal motion of the molecules is changed to a directed motion. Hence, the pumping process in a turbomolecular pump results from the directed motion of the gas molecules from the inlet flange to the forevacuum port. In the molecular flow range- i.e. at pressures below 10-3 mbar (0.75 x 10-3 Torr) - the mean free path of the gas molecules is larger than the spacing between rotor and stator blades (typically some tenths of a millimeter). Consequently, the molecules collide primarily with the rotor blades with the result that the pumping process is highly efficient. In the laminar flow range- i.e. at pressures higher than 10-1 mbar (0.75 x 10-1 Torr) - the situation is completely different. The action of the rotor is diminished by the frequent collisions between the molecules. Therefore, a turbomolecular pump is not capable of pumping gases against atmospheric pressure and has to be backed by an adequate fore-vacuum pump. To create the directed motion of the gas molecules mentioned above the tips of the rotor blades have to move with supersonic velocity. Hence, a high rotational speed of the rotor is required. In case of LEYBOLD turbomolecular pumps the rotor speeds vary from about 36,000 rpm for large rotor diameters (e.g. TURBOVAC 1000, Å 20 cm (7.87 in.)) to 72,000 rpm for small rotor diameters (e.g. TURBOVAC 50, Å 6 cm (2.36 in.)

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Accessories:

• Fluids
• Intake filter
• Exhaust filter
• Gauge
• Maintenance kit
• Hose

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