In what part of a pump can you find the packing or mechanical seal?

The correct answer is the stuffing box, as it is specifically designed to contain the packing or mechanical seal that prevents leakage of liquid out of the pump. The stuffing box houses the packing material, which is made of various materials such as graphite or PTFE, and is sealed around the shaft to minimize wear and prevent fluids from escaping. In many mechanical seals, they provide an effective barrier against leakage, especially in applications involving high pressures or temperatures.

In contrast, the casing serves as the outer shell of the pump, housing the internal components but not specifically containing the sealing method. The impeller is the component that moves the fluid, and while it plays a critical role in the pump's operation, it does not incorporate the packing or mechanical seal itself. The motor powers the pump but is separate from the fluid containment and sealing functions necessary to prevent leakage.