Gland Overfill

With a similar appearance to extrusion, gland overfill failure mode also has the unique, “tails” of O-ring material. The difference is the tails extend out from both corners of the groove, and, if significant, you may see the round O-ring cross section now resembles a square.

Overfill is caused by too much O-ring in a groove, which results in the gland being overfilled. There are a number of root causes, including:

• The groove is too shallow for the thickness of the O-ring
• The groove is too narrow, more like a square than a rectangle
• Application fluids cause the O-ring material to swell more than the groove width allows
• Application temperatures cause the O-ring material to expand, more than the groove width allows. This occurs with FFKM seals at high temperatures
• The wrong O-ring (too thick) was placed in the groove, or the groove was cut the wrong size

Parker recommends a gland design where the O-ring has a maximum material condition gland fill of 90%. This allows a bit of space for the O-ring to swell due to thermal expansion or volume change. This guidance can be stretched to 95% for applications where the expected fluid swell is low, or high temperature thermal expansion is limited. The Sizing and Selector guide has a feature which allows you to design for high temperature thermal expansion or expected volume change due to fluid interaction.