What does seat leakage mean in valve terminology?

• A. Leakage around the seat that prevents sealing
• B. Leakage past stem packing
• C. Leakage due to external piping
• D. Increase in torque

Answer: (A)

Seat leakage is when fluid finds a path around the sealing interface between the valve’s closure element and the seat, so even with the valve fully closed, there is a leak past that seal. The closure member (disc, plug, or ball) must press tightly against the seat to form a true shutoff, but wear, damage, debris, or imperfect seating can leave tiny gaps that allow flow. This is why it is described as leakage around the seat that prevents sealing.

Leakage past stem packing would be along the stem seal instead of the seat interface, outside piping leaks involve external connections, and an increase in torque points to sticking or binding rather than a flow path through the seating surface.