Question 392General Subjects - Assistant Engineer
70% to passWhich 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?
APacked stuffing box glands are subject to wear, but mechanical seals are not.
BPacked stuffing box glands must be cooled by the liquid being pumped, but mechanical seals do not require cooling.
CIf 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.
DThe sealing surface of a mechanical seal is parallel to the shaft, but the sealing surface of a packed gland is perpendicular to the shaft.
AI Explanation
The correct answer is C. The main difference between a stuffing box gland and a mechanical seal is that if the packing in a stuffing box gland fails, the leak can be temporarily stopped by tightening the gland. However, if a mechanical seal fails, the entire seal must be replaced to stop the leakage, as there is no way to "tighten" a mechanical seal. The other options are incorrect because: A) Both stuffing box glands and mechanical seals are subject to wear over time. B) Mechanical seals can be designed to operate without external cooling, depending on the application. D) The orientation of the sealing surface is not the primary difference between the two sealing methods.
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