Failure Pattern
Spiral failure is 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
Spiral failure is caused when some segments of the O-ring slide while other segments simultaneously roll. At a single point on its periphery, the O-ring becomes caught on an eccentric component, or against the cylinder wall, causing twisting and development of 45-degree angle, 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

O-RING RULE OF THUMB #1

A stretch greater than 5% on the O-ring I.D. is not recommended because it can lead to a loss of seal compression due to reduced cross-section. » Learn More