Investigation of leakage contribution from different air seal components

Abstract: Mountain biking is a sport where riders bike on trails, varying in slope and difficulty. Mountain bikes are generally equipped with suspension on the front wheel and often also on the rear. Some types of rear shocks use pressurized air for a spring action instead of the traditional metal coil. Air is sealed inside the shock’s air can by means of X-ring seals, providing a spring force on the wheel. It is of great importance that the sealing system performs as intended so the air spring does not quickly lose pressure during use. An experimental plan is conducted in an attempt to estimate the effects of seal dimension, lubrication and surface roughness on air leakage for more robust shocks. Accelerated tests were performed in a dynamometer, believed to repeatedly cause significant wear on the shock’s air seal within 24 hours. Nineteen tests were carried out, for a duration up to 72 hours, with variations to test parameters such as stroke length and frequency. The expected failure modes did not occur in any of them. Eleven tests showed no signs of failure while the other eight failed due to unexpected components breaking or wearing out. The shock’s main seal was found to wear out faster than the air seal, causing leakage within the air spring, between its positive and negative air chambers. This unforeseen failure needs further examination with tests conducted on more shock types.