Which of the following could indicate imbalance in a rotating machine?

• A. Damaged impeller
• B. Worn bearings
• C. Misalignment
• D. Balanced impeller

Answer: (D)

Imbalance shows up as vibration because uneven mass distribution in the rotor creates fluctuating centrifugal forces as it spins. A damaged impeller directly changes the rotor’s mass distribution, producing an imbalance and resulting vibration, rough running, or abnormal wear—these are classic signs to look for. Worn bearings can allow more movement and vibration and may accompany imbalance, but they don’t themselves change the rotor’s mass balance. Misalignment also causes vibration from geometric offset and bending loads, not from an uneven mass in the rotor. A balanced impeller, by definition, minimizes imbalance, so it would not indicate imbalance. Therefore, a damaged impeller is the direct indicator of imbalance.