Which of the following statements represents the main difference between a stuffing box gland and a mechanical seal for sealing the shaft of a centrifugal pump?

Correct Answer: Option C — If packing fails, the pump can be kept running temporarily by tightening the gland, but if a mechanical seal fails it must be totally renewed to stop the leakage.

Stuffing boxes utilize adjustable packing that can be compressed to compensate for wear, allowing temporary operation. Conversely, mechanical seals rely on precision-lapped faces; once these faces are damaged or the secondary seals fail, the unit loses its sealing capability entirely and requires a complete overhaul to restore functionality.