A shaft can be bent during shipping, installation, etc. Bent shaft generates high vibration and creates a lot of stress on other components during operation. If there is no action taken, catastrophic failure will result. It is therefore important to be able to recognize such a fault.
Bent shaft can be identified by measuring vibration on one of the bearings. The dominant vibration is normally at 1X if the bend is near the center of the shaft. We will see 2X vibration if the bend closer to the coupling. We can still misinterpret this data from misalignments or any other types of faults. Vertical and horizontal axis measurements will also often reveal peaks at 1X and 2X, but the key is the axial measurement. Phase measurement is a good test used to diagnose a bent shaft. The phase at 1X measured in axial directions on the bearings will be 180o out of phase. This confirms that the fault is bent shaft.