O-ring applications are categorized by the type of motion that is happening between the two surfaces. Static applications involve sealing between two parts that do not move. Dynamic sealing refers to applications where the two parts are moving in relation to each other. The following drawings depict static and dynamic sealing. Used in situations involving reciprocating, rotating or oscillating machine movement relative to the o-ring, dynamic seal performance may be substantially affected by a number of operating environmental factors. Such factors include: seal swell in fluids, surface finish of metal parts, lubrication, system pressure, thermal cycling, o-ring squeeze, o-ring stretch and friction As many of these factors are interrelated, it is important to consider ALL of the in dynamic sealing situations. Rubber Fab highly recommends pretesting in specific dynamic applications to determine acceptable life cycle.