Question 420General Subjects - 1st Asst/Chief

The correct answer is B) Mechanical unbalance. When vibration occurs at the same frequency as the motor's rotational speed, and the displacement in the radial direction is twice that of the axial direction, this is a classic indicator of mechanical unbalance. Mechanical unbalance occurs when the center of mass of the rotating assembly (e.g., motor, pump, or other equipment) is not aligned with the center of rotation. This creates an imbalance that results in vibration at the rotational frequency, with greater radial displacement compared to axial displacement. The other options are not the correct explanation for this vibration pattern. Loose foundation bolts would likely result in vibration at lower frequencies, a bent motor shaft would cause vibration at multiples of the rotational speed, and rubbing would generally produce vibration at higher frequencies.