Seal Stability

Dynamic stability is integral to a seal’s performance, allowing the lip to effectively contact the sealing surface, eliminating rocking and pumping effects and promoting an even wear pattern at the sealing contact point. Instability can create leakage and seal damage. A typical instability malfunction known as “spiral failure” can occur when o-rings are used in reciprocating applications. Due to frictional forces that occur while the system is cycling, the o-ring will
tend to roll or twist in the groove, causing leakage and even possible breakage. A square geometry will tend to resist this better than a round profile, but is not impervious to instability failure. Rectangular geometries provide the best stability in dynamic applications.

Other less obvious factors that influence the stability of a seal are:
• Percent gland fill
• Hardness or stiffness of the seal material
• Rough surfaces which create high friction
• Cross-section (larger is better)
• Design features of a seal (i.e. stabilizing lip, nonsymmetrical design). Figure 2-8 illustrates how
design features can make a seal more stable. In the first FEA plot, the seal is centered in the gland and does not incorporate a stabilizing lip. In the second plot, the seal is loaded against the static gland and includes a stabilizing lip. Stability has been enhanced by the design changes.