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 A — 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.

Packed stuffing boxes allow for controlled leakage and adjustment via gland tightening while the pump is operational. Conversely, mechanical seals are precision-engineered assemblies; once the internal faces or secondary seals fail, the entire unit must be replaced, as they cannot be adjusted to compensate for wear or damage.