Failure Pattern: Easily identi ed by a marked increase in seal dimensions and occurring in both static and dynamic situations. Results in a reduction of physical properties and can result in improper sizing between seal and gland. Dynamic applications are especially prone in that friction accelerates seal failure.
Problem Sources: Like a sponge, the seal absorbs the surrounding uids and swells to the point of malfunction because of incompatibility between seal compound and system environment (i.e. chemical incompatibility, high humidity, etc.).
Suggested Solutions: Employ a chemically compatible O-ring material.
Failure Pattern: Generally found on long stroke, hydraulic piston seals, the surface of the O-ring exhibits a series of deep, spiral 45 degree angle cuts.
Problem Sources: Caused when some segments of the O-ring slide while other segments simultaneously roll. At a single point on its periphery, the O-ring gets caught on an eccentric component, or against the cylinder wall, causing twisting and development of 45 degree angle, surface cuts. Contributing Conditions Include: Eccentric components... Wide clearance combined with side loads... Uneven surface nishes... Inadequate lubrication... Excessive O-ring material softness... Too slow stroke speeds.
Suggested Solutions: Check for out-of-round cylinder bore... Decrease clearance gap... Machine metal surfaces to 10-20 micro-inch nish... Improve lubrication (consider internally-lubed O-rings)... Increase O-ring material hardness and/or cross section... Employ anti-extrusion back-up rings.