FAA Powerplant Written Practice Test

Why is a vent line equipped on an aircraft reciprocating engine oil tank in a dry sump lubricating system?

1. To allow oil to escape

2. To prevent pressure buildup

3. To regulate oil flow

4. To facilitate oil replacement

The correct answer is: To prevent pressure buildup

In a dry sump lubricating system used in aircraft reciprocating engines, a vent line is crucial for preventing pressure buildup within the oil tank. As the engine operates, the temperature of the oil can fluctuate, and if the tank were to become sealed without a vent, the rising temperature would cause the oil to expand, leading to increased pressure. This pressure buildup can create a risk of oil leaks, which could adversely affect engine performance and safety. By allowing air to enter the tank as the oil level changes and temperature varies, the vent line ensures that the oil tank can maintain atmospheric pressure. This design feature is essential for proper functioning, as it helps to prevent potential issues such as oil aeration and foaming that could compromise the lubricating properties of the oil. Furthermore, maintaining proper pressure ensures that the oil pump can effectively draw oil from the tank without the risk of cavitation, thereby ensuring the reliability of the lubrication system.