Due to the necessarily high rotational speeds, the rotors of turbomolecular pumps require precise balancing, i.e., achieving coincidence of inertial and rotational axes. The importance of a balanced rotor and the effect of unbalance on the performance of the pump is discussed. The detection of unbalance and the measurements of amplitude and phase of vibrations are considered. Selection of vibration detecting transducers, stroboscopic and digital instrumentation, and data acquisition computers for the printing of results will be covered. Unbalance can be corrected by different methods: addition, removal, or displacement of masses. A four‐leafed balancing device is described and a computer‐assisted balancing method is illustrated utilizing a transfer function associating unbalance and vibration. In addition, the following subjects are considered: deformation problems, flexible rotors, nonlinear behavior with increasing rotational speeds, temperature drift, and artificial aging.

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