Introduction to Industrial Maintenance Practice Test

The key idea is how the seal medium actually stops leakage. A mechanical seal relies on two very smooth faces that are pressed together, forming a very thin gap that is kept lubricated by the process fluid. This faces-and-spring arrangement minimizes leakage and wear because the seal is a tight, boundary surface, not a packing material around the shaft.

In contrast, a packing gland seals by squeezing a braided packing material around the shaft with a gland follower. The seal works mainly by friction and compression of that rope-like packing, which can wear the shaft and leak more over time and typically needs periodic repacking or adjustment.

So the statement that best differentiates them is that the mechanical seal uses faces pressed together to prevent leakage, with lubrication provided by the pumped fluid. The other options either describe packing behavior instead of the mechanical-seal mechanism, claim identical operation, or claim no maintenance is needed, which aren’t accurate.