Ask the Experts

We are experiencing seal failure on equipment at our plant that is used primarily outdoors. We checked and rechecked seal dimensions, etc. The new seal operates properly for a while, but over time it fails. Any suggestions?

Both static and dynamic seals exposed to atmospheres containing ozone and other air pollutants can be subject to failure due to cracking. This failure mode is marked by the appearance of many small surface cracks perpendicular to the direction of stress.

Ozone attack of the polymer chains causes the O-ring cracking. The solution is to employ O-ring elastomers that are resistant to ozone attack. Click here for a chemical compatibility table that can assist you in your selection.

What do I need to know about the effect of temperature when considering the proper material for my seals?

Over time, excessive heat degrades O-ring materials physically and/or chemically, which may render them non-functional. Excessive heat is known to cause O-ring materials to both swell and harden, taking a permanent compression set (deformation of shape) within the gland.

Cold temperatures, without proper material selection to resist the effect of extreme cold, results in O-ring shrinkage and possible leakage due to reduction in surface contact. Extreme cold also effects O-rings by making them brittle and less flexible.

For optimum sealing performance, always attempt to keep the O-ring application within the temperature ranges listed on the individual material data sheets shown. Click here for a Material Selection Guide.

What is a back-up ring and how should one be used?

A back-up ring is a washer like device of a relatively hard, tough material installed in the gland on the downstream side of the O-ring to prevent O-ring extrusion into the diametrical gap while under pressure. When using only one back-up ring, be sure to install it on the low pressure side of the O-ring.

Ask the Experts yourself.

If you've got sealing questions, you can ask the experts at Apple Rubber for answers. Visit our web site and submit your question or questions using our Engineering Assistance Request form and we will respond as quickly as possible.