Stem seal is traditionally considered the most critical pressure containment boundary of a valve; in fact on top of the criticality of physical parameters of process fluids (Pressure,
Temperature…) and its chemical aggression, stem gasket shall also withstand repeated
dynamic strokes.
Stroke may consist on pure linear (rising stem valves) or rotational (quarter turn valves)
movement; sometimes linear and rotational movements are simultaneously combined.
Each of the above stroke movements is characterized by unique friction/wear/abrasion conditions, therefore stem gaskets may need different design features and they shall be manufactured with materials specifically selected to better suit the operations; but all the different stem gasket designs do have a unique goal: they should be, from the point of view of tightness, comparable with all other static gaskets placed on valve pressure boundary.