Imbalance in Overhung Machines
In a machine with an out of balance overhung, or cantilevered, rotor such as a fan will produce 1X vibration in the axial direction as well as some radial and tangential at the nearest bearing to the rotor. This is because the imbalance creates a bending moment on the shaft, causing the bearing housing to move axially. Examples of overhung rotors are close-coupled pumps, axial flow fans, and small turbines.

Overhung Rotor Imbalance
The bearing closest to the overhung rotor will usually show the highest radial 1X-vibration levels.
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