O-ring Failure

When it comes to fluid-power systems, O-rings are the most commonly used seals. However, elastomeric O-rings are not like most of the other materials that designers and engineers encounter. And the reason for this is because O-rings must deform to function properly.

As the name of the O-ring implies, they are round. O-rings are installed into the cavities that are known as glands and then compressed. The resulting 0 clearance within the gland provides the seal that then blocks the flow of gases and liquids. This simple arrangement has served many fluid-power systems well, however, success will still require careful selection, design, and installation procedures.

O-rings can commonly fail in their applications because of the combined adverse effects of many environmental factors. Experience with these systems has shown the most common causes of O-ring failure can be:

  • The incorrect O-ring size
  • The improper gland design, which allows for too much or too little compression, not enough space for displacement under the compression, or a tolerance stack up
  • The improper O-ring installation
  • The inadequate O-ring lubrication
  • The incompatibility between the O-ring elastomer and environmental elements that it must contract

All of the different stresses that act on O-rings can be quite complex and difficult to evaluate. Therefore, both the O-ring size and compound should be tested in the real environment of its service. Below is an example of a common type of failure that can occur:

Failure without visible evidence on the seal

The failure pattern

Of the many different types of seal failure, this one is among the most difficult to diagnose because of the result of the problem is not visible on the actual O-ring.

The problem sources

Insufficient compression, eccentric-shaped components, tolerance stack-up, any parting lines and/or flash left on the O-ring from the molding process, and an improper volume relationship between the seal and the gland.

At Fuzion Trading, we supply the very best quality hydraulic seals and O-rings. For more information on our products, visit our website at www.fuziontrading.co.za.