To prevent leakage at the point where the shaft protrudes through the case, either _________ are used to seal the space between these two.

• A. O-Rings
• B. Gaskets
• C. Epoxy Fillers
• D. Packing rings or mechanical seals

Answer: (D)

When a shaft passes through a casing, you need a dynamic seal that can accommodate rotation and the pressure of the fluid. Packing rings (in a stuffing box) compress around the shaft to reduce leakage while the shaft turns, and mechanical seals provide two mating surfaces pressed together to form a tight seal against rotation. These approaches are specifically designed for sealing the space around a rotating shaft.

O-rings and gaskets are typically used for static joints or surfaces with little to no movement; they’re not ideal for a rotating shaft through a case because they can wear, extrusion, or fail under ongoing rotation. Epoxy fillers aren’t suitable for a moving interface either, as they don’t provide a durable, serviceable seal around a rotating shaft.

So the best fit here is packing rings or mechanical seals.