Question 312General Subjects - QMED

The correct answer is B) Water under positive pressure. Mechanical shaft seals used on water service pumps require a positive pressure water supply to the seal faces to ensure proper lubrication and prevent the buildup of foreign matter on the seal surfaces. The positive pressure helps push the water between the seal faces, keeping them lubricated and preventing contaminants from entering. Using water under negative pressure or oil under any pressure would not provide the necessary lubrication and could lead to seal failure.