ABSTRACT
The molecular drag pumps are designed with different geometrical configurations, but their pumping effect is based on the same physical principle, which is the momentum transfer from fast-moving surfaces to gas molecules. The smaller backup pumps contaminate vacuum less. Turbomolecular pumps have been designed with horizontal and vertical constructions. The mechanical bearings of turbomolecular pumps can be lubricated by lubrication fluids and special greases with low vapour pressures. Turbomolecular pumps are available with standard constructions for pumping ordinary gases as well as construction for pumping corrosive gases. Turbomolecular pumps can be equipped with magnetic levitation of the rotors on the high-vacuum side for smaller pumps. The larger pumping area consequently yields the larger pumping speed. The pumping speed also depends on the mass of gas molecules. Regenerative vacuum stages combined with high-vacuum Holweck stage can discharge gases into the atmospheric pressure and can achieve high vacuum.
