What is true about packing in the stuffing box of a centrifugal pump?

In the context of a centrifugal pump, the packing in the stuffing box serves an important function in controlling leakage along the shaft. While the ideal scenario would be to eliminate all leakage for efficiency and safety, it is recognized that some leakage needs to occur to ensure proper lubrication and cooling of the packing material. Allowing a small amount of leakage minimizes wear on the pump's shaft and packing while maintaining a balance between effective sealing and the prevention of overheating.

The packing material is specifically designed to absorb and tolerate some liquid, which helps to create a seal while also enabling the fluid to cool the packing and the shaft. If the packing stopped all leakage entirely, it might lead to excessive heat buildup and eventual failure of the packing material, which could cause more severe operational issues.

Other options suggest either an unrealistic expectation for no leakage or unnecessary restrictions about the nature of the packing material. Packing does not need to be metallic; in fact, many centrifugal pumps use non-metallic materials for their packing due to their excellent sealing properties and resistance to corrosion, making them suitable for various applications.