AVM Powerplant Practice Test

Seals around a turbine engine’s main bearing must keep oil in place while withstanding extreme speeds and temperatures. The typical options are labyrinth seals and carbon rubbing seals. Labyrinth seals provide a non-contact barrier: the shaft passes through a chamber with a long, winding path that makes it very difficult for oil to leak out, and since there’s no metal-to-metal contact, wear and heat buildup are minimized. Carbon rubbing seals, on the other hand, use carbon-based seal faces that lightly rub against a mating surface to form a tight seal, offering excellent high-temperature performance and oil compatibility with controlled friction. Elastomer or silicone rubber seals aren’t favored here because they can degrade, swell, or lose dimensional stability under the combination of oil exposure and high temperatures found in the bearing area. Materials like Teflon-containing seals also don’t provide the reliable high-temperature, long-life performance required in this environment. So the usual choices are the robust, heat-tolerant labyrinth and carbon rubbing seals.