As the name implies, spiral failure results when the O-ring develops spiral surface cuts. These cuts typically recur at regular intervals along the seal’s exterior. At its most basic level, spiral failure results from instability of the seal, which is unable to adequately hold its intended position within the gland. Generally seen in long-stroke hydraulic or pneumatic (piston and rod) seals, spiral failure is most likely to occur in O-rings with a large inside diameter (I.D.) to cross-section (W) ratio.

This is because the O-ring doesn’t have enough strength to resist the twisting forces that naturally develop during dynamic movement. Part of the O-ring rolls as part of it slides, and this spiraling motion causes the cross-section to be twisted and cuts to develop on the seal’s surface.

Other factors that may also contribute to spiral failure include uneven surface finishes, lack of proper lubrication, and installation error. Figure 137 is an example of O-ring failure due to spiraling.

Possible solutions to spiral failure include using 1) as large a seal cross-section as possible, 2) harder compounds, 3) smoother surface finishes, and 4) lubrication. In some cases, it may be preferable to use an alternate seal cross-section that will be more stable within the gland. For more information on O-ring alternatives, see Exploring Other Options.