Mechanical shaft seals used on water service pumps require lubrication of the seal faces to minimize deposits of foreign matter on those surfaces. Which of the following pressures and lubricants are required?

Correct Answer: Option B — Water under positive pressure.

Mechanical seals require a positive pressure fluid film between the faces to act as a lubricant and coolant. In water service pumps, this is typically provided by the pumped fluid itself or an external flush line, ensuring the seal faces do not run dry, which would cause rapid thermal degradation.