Contact with brake fluid inevitably causes either seal swelling or shrinkage to some degree, depending on the elastomeric compound. This results in excessive or insufficient compression and leads to seal failure. Swell or increase in volume is also usually accompanied by a decrease in hardness, which causes a reduction in abrasion and tear resistance and may allow seal extrusion under high pressure. Also, seal failure due to swelling is accelerated in dynamic applications because of the heat generated from friction.
Ethylene Propylene, when specifically compounded for brake fluid service, is the elastomeric compound of choice. It allows a relatively nominal amount of swell while attaining service temperatures to 250°F. With the addition of different types of brake fluid, please contact Apple Rubber for assistance in the matching of elastomer compound to service fluid. Some automobiles use mineral oil-based brake fluids which can attack EP rubber.