Overgreasing a plug valve assembly is most likely to cause leakage at which interface?

Overgreasing a plug valve assembly is most likely to cause leakage at which interface?

• A. Between the seat and disc
• B. Between the segment and body
• C. Between the gland and stem
• D. At the handwheel

Answer: (B)

When a plug valve is properly sealed, the seal is formed by a segment sitting tight between the plug and the valve body. Overgreasing pushes lubricant into that tight interface. The extra grease creates pressure in the tiny clearance at the segment-to-body boundary, causing the segment to deform or extrude slightly and breaking the seal there. That creates a leakage path right at the segment–body interface, which is why this is the most likely place for a leak. Leakage at the gland–stem interface would come from packing problems, not from overgreasing the valve itself, and the seat–disc interface isn’t the typical path opened by excess grease in a plug valve. The handwheel location isn’t a sealing surface, so it wouldn’t be the leakage path.

When a plug valve is properly sealed, the seal is formed by a segment sitting tight between the plug and the valve body. Overgreasing pushes lubricant into that tight interface. The extra grease creates pressure in the tiny clearance at the segment-to-body boundary, causing the segment to deform or extrude slightly and breaking the seal there. That creates a leakage path right at the segment–body interface, which is why this is the most likely place for a leak.

Leakage at the gland–stem interface would come from packing problems, not from overgreasing the valve itself, and the seat–disc interface isn’t the typical path opened by excess grease in a plug valve. The handwheel location isn’t a sealing surface, so it wouldn’t be the leakage path.