What is the purpose of bypass valves?

• A. To regulate oil temperature.
• B. To measure oil pressure.
• C. To filter oil.
• D. Installed as a fail safe on components that could possibly cause a restriction in oil flow.

Answer: (D)

A bypass valve exists to keep oil flowing even when a component or path starts to restrict flow. In an aircraft oil system, staying lubricated is critical, so the valve opens when a potential restriction—like a clogged filter or a narrow passage—would raise the pressure drop too high. By providing a secondary path, it prevents oil starvation to bearings and gears and lets the system continue operating long enough for the issue to be addressed. It’s a protective measure, not something that regulates temperature, measures pressure, or filters oil. If the filter gets clogged, the bypass allows unfiltered oil to reach critical parts rather than stopping lubrication entirely.