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, the development of 45 degree angle and surface cuts.
Contributing Conditions:
- Eccentric components
- Wide clearance combined with side loads
- Uneven surface finishes
- 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 finish
- Improve lubrication (consider internally-lubed o-rings)
- Increase o-ring material hardness and/or cross section
- Employ anti-extrusion back-up rings