FAA Powerplant Written Practice Test

What type of seals are commonly used in turbine engine main bearings?

1. Magnetic and rubber seals

2. Cleated and thermal seals

3. Labyrinth and/or carbon rubbing

4. Silicone and foam seals

The correct answer is: Labyrinth and/or carbon rubbing

The use of labyrinth and/or carbon rubbing seals in turbine engine main bearings is a well-established practice due to their effectiveness in preventing the leakage of oil and contaminants while allowing for some axial and radial movement. Labyrinth seals work by creating a series of grooves and ridges that form a complex path for the oil to navigate, which significantly reduces the possibility of fluid escaping from the bearing compartment. This design minimizes the fluid loss while maintaining the necessary lubrication of the bearings, which is critical for the engine's performance and longevity. On the other hand, carbon rubbing seals are designed to work with a rotating shaft, where a carbon face is held against the shaft, providing a nearly frictionless seal that helps contain engine oil. The properties of carbon allow it to withstand high temperatures and provide good wear resistance, which is essential in harsh turbine engine environments. These sealing methods are particularly important because turbine engines operate under extreme conditions, including high temperatures, speeds, and pressures. Ensuring a reliable seal contributes to both operational efficiency and the overall reliability of the engine.