FAA Powerplant Written Practice Test

Which valve type is responsible for stopping oil from entering the main accessory case when the engine is not running?

1. Relief valve

2. Check valve

3. Solenoid valve

4. Bypass valve

The correct answer is: Check valve

The check valve is designed to prevent the backflow of oil, ensuring that it does not enter the main accessory case when the engine is not operating. This function is crucial because, during times when the engine is not running, oil can flow backward through the lubrication system, potentially leading to issues such as oil leakage and contamination of engine components. The check valve allows oil to flow in one direction only—toward the engine where it is needed for lubrication—while effectively blocking any reverse flow when the engine is off. This one-way operation is essential for maintaining proper oil pressure and integrity within the engine system, as it ensures that oil remains in the appropriate parts of the engine without spilling into areas that could cause inefficiencies or damage. Relief valves, by contrast, are typically designed to regulate pressure in the system and do not serve the function of stopping oil from flowing back. Solenoid valves control the flow of fluid via electrical signals and are generally used for different operational scenarios. Bypass valves are employed to redirect oil around a filter or other component but do not prevent backflow when the engine is not running. Thus, the check valve is the component specifically tasked with stopping oil from entering the main accessory case in inactive conditions.