|
The molecular drag stages in the modern day turbomolecular pumps are employed to improve the pumping efficiency in the continuum viscous region. The design of the drag stages consists of stationery helical pumping grooves cut into the surface of a cylinder surrounded by a close-fitting smooth cylindrical bore spinning concentrically about the cylinder. During operation, the molecular drag stages act as a dynamic gas seal preventing the back streaming of the oil vapors entering the process system from backing pumps. An experimental evaluation of dynamic gas seal effect has been made which is in close proximity of the theatrically computed values. At the end, advantages of the dynamic gas seal in the turbo-molecular pumps are presented. |