FAA Powerplant Written Practice Test

Which type of valve prevents oil from entering the main accessory case when the engine is not running?

1. Butterfly valve

2. Check valve

3. Solenoid valve

4. Regulating valve

The correct answer is: Check valve

The check valve is specifically designed to allow fluid to flow in one direction while preventing backflow. In the context of an aircraft engine’s oil system, the check valve prevents oil from leaking into the main accessory case when the engine is not running. This is crucial for maintaining proper oil pressure and ensuring that the oil system is functioning correctly when the engine starts. The check valve's operation helps to keep oil pooled where it is needed for lubrication once the engine is active, thus preventing potential damage that could arise from oil stagnation or improper flow distribution while the engine is off. The other types of valves mentioned do not fulfill this specific function. A butterfly valve typically regulates flow and is not designed to prevent backflow. A solenoid valve is electrically controlled and may be used in various systems but does not inherently possess backflow prevention capabilities. A regulating valve is designed to maintain a specific pressure or flow rate rather than to prevent backflow. Hence, the check valve is the correct answer for managing oil flow in this context.