Why Do O-Rings Extrude?
O-ring extrusion: A Quick Overview
An O-ring may look simple, but under pressure, a small amount of clearance in the wrong place can cause a big sealing problem.
One common failure mode is O-ring extrusion. (Estimated reading time: 3 minutes)
What Is O-Ring Extrusion?
Extrusion occurs when system pressure forces part of the O-ring into the clearance gap between two mating components.
As pressure increases, the elastomer can begin to push into that gap. Over time, the material may become damaged, creating a characteristic nibbled, torn, or chewed appearance along the edge of the O-ring.
Eventually, that damage can lead to leakage or complete seal failure.
What Causes Extrusion?
Several factors can increase the risk of O-ring extrusion:
- High pressure
The greater the system pressure, the more force is pushing the O-ring toward the clearance gap. - Large clearance gaps
More space between mating components gives the elastomer more room to extrude. - Soft O-ring materials
Lower-durometer compounds are generally easier to deform under pressure than harder materials. - Elevated temperature
Higher temperatures can soften some elastomers, making extrusion more likely. - Pressure cycling or movement
Repeated changes in pressure or component movement can accelerate damage once extrusion begins.
Can a Harder O-Ring Solve the Problem?
Sometimes.
Increasing the durometer of the O-ring can improve extrusion resistance. For example, moving from a 70 Shore A compound to a harder material may help in a higher-pressure application.
But hardness is only one part of the sealing system.
The correct solution depends on the operating pressure, gland dimensions, extrusion gap, temperature, media, and whether the application is static or dynamic.
When Should You Use a Backup Ring?
A backup ring is installed next to the O-ring to help prevent the elastomer from being forced into the clearance gap.
Backup rings are commonly used in higher-pressure hydraulic and pneumatic applications or whenever the combination of pressure and clearance creates an unacceptable extrusion risk.
Depending on the direction of pressure, an application may use a backup ring on one side of the O-ring or on both sides.
Look at the Entire Sealing System
When an O-ring repeatedly fails from extrusion, simply replacing it with another O-ring of the same size and material usually won’t solve the underlying problem.
The seal, gland, clearance, material hardness, pressure, temperature, and operating conditions all work together.
Understanding why the O-ring failed is often the first step toward choosing a better sealing solution.
Performance Seals works with customers to evaluate O-ring materials, sizes, backup rings, and other sealing options for industrial applications.
How Performance Seals Can Help
Have an O-ring that keeps failing? Send us the application details — or even a picture of the failed seal — and our team can help you determine what may be happening.
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Need Help with O-Ring Extrusion?
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