A friction pump, which is equipped with at least one actively controlled magnetic radial bearing, wherein, in order to satisfy the extreme requirements necessary through the tight tolerances of pump elements and an emergency bearing, the high rotational speed and the magnetic support,Sweage pumps &Sludge pumps a special control arrangement for the cooperation of rotor, positional sensors and the magnetic bearing control loop so that a safe operation of the pump at extreme requirements is assured in a simple manner without the use of any additional constructional elements. Friction pumps produce, in the range of molecular flow,BALANCING VALVES a constant pressure ratio and, in the range of laminar flow, a constant pressure difference. In friction pumps of the Gaede, Holweck or Siegbahn, construction type, for instance the pressure ratio in the molecular range as well as the pressure difference in the laminar range are especially high at very narrow gaps. Turbomolecular pumps, being a refinement of friction pumps of the earlier type of construction, produce a very high pressure ratio in the molecular range even at larger gaps. In the laminar range, however, they produce only a very small pressure difference. A friction pump constructed according to Holweck is, for instance, described in Comptes rendus Acad. Science 177 (1923) 43 and following. A friction pump of the type built by Siegbahn is described in the Archives of Mathematics and Astrology and Physics 30 B (1943). The basic construction and the mode of operation of a turbomolecular pump according to Becker are described in Vacuum Technology 9/10 (1966). The operational range of turbomolecular pumps is limited towards higher pressures, since they are only fully effective in the molecular flow region. This molecular flow region is bounded by that pressure, for which the average free travel length of the molecules comes down to the order of magnitude of the vessel dimensions. Therefore, turbomolecular pumps operation only in combination with pre- or fore-vacuum pumps, generally two stage rotary vane is now pumps. If, however, it can be achieved to extend the operating range of turbomolecular pumps towards higher pressures, the effort to produce the necessary fore-vacuum can be reduced. In that case, for instance, single stage rotary vane pumps, and after would be sufficient, or, the oil tight rotary vane pumps could be replaced by dry diaphragm type pumps. The present invention provides a friction pump with one or several pump stages for the conveyance of gases, wherein the support of the rotor is achieved by magnetic bearings with at least one actively controlled radial bearing. The radial position of the rotor relative to the housing or the stator arrangements is obtained or determined by position sensors. At least one mechanical emergency bearing exists, characterized in that the magnetic radial bearing, the position sensors and the controller arrangement for the magnetic bearing cooperate in such a way, that the geometric center of the rotor in the emergency bearing can be determined and the rotor can be centered in that position

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2012-01-19

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