Which of the following is NOT listed as a pump seal type?

• A. Packing
• B. Throttle bushing
• C. O-ring
• D. Mechanical

Answer: (C)

In pump sealing, the main categories used to prevent leakage at the shaft are packing, mechanical seals, and throttle bushings. Packing uses braided material packed around the shaft in a stuffing box and relies on compression to seal. Mechanical seals are purpose-built assemblies with a rotating part and a stationary part that create a tight interface under pressure. A throttle bushing acts as a component in some seal arrangements to control clearance and leakage, helping manage how the seal performs under operating conditions.

An O-ring is a versatile seal element, but it isn’t typically treated as a primary pump seal type in this kind of taxonomy. O-rings are often used as secondary seals or static seals within a pump assembly or around flanges, rather than as the main method for sealing a rotating shaft in a pump. That’s why O-ring is the option that isn’t listed as a pump seal type in this context.