US Patent 7614844 Vacuum pumping arrangement

A regenerative pumping mechanism comprises a rotor having a series of blades positioned in an annular array on one side of the rotor, and a stator having an annular channel within which the blades rotate. In order to control the axial clearance between the rotor and the stator, an axial magnetic bearing actively controls relative axial movement between the rotor and the stator. This can allow the pumping mechanism to provide controllable axial sealing between the rotor and the stator, as opposed to radial sealing.