Eccentricity

Eccentricity is often confused with unbalance because it also manifests as increases in vibration at the shaft rotational rate (1x) in the vertical and horizontal axes. The difference is that you cannot solve an eccentricity problem by balancing the rotor. You can see this clearly in the video.

One way to determine if the problem is unbalance or eccentricity is to check the rotor with a dial indicator. If you turn the rotor by hand, it will not move in the radial directions if it is unbalance. It will move if it is eccentricity. (It will also move if it is a bent shaft - read more about that here: https://zencovibrations.com/diagnosin...  )

You might also be wondering why your attempts to balance the rotor are not working. One explanation could be that the rotor or, a component mounted on the rotor, is eccentric.

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