FAA Aviation Mechanic Airframe (AMA)Hydraulic and Pneumatic SystemsMedium
An aircraft's hydraulic pump output drops significantly due to a partial pump failure. The system is designed so that flight control actuation continues to receive adequate flow while landing gear and flap operation are automatically restricted until flow is restored. Which component provides this function?
- ASequence valve
- BPressure-reducing valve
- CPower transfer unit
- DPriority valve
Show answer & explanationAnswer & explanation
Correct answer: D. Priority valve
A priority valve ensures that essential systems, such as flight controls, receive hydraulic flow before non-essential systems like landing gear or flaps when pump output or system pressure is reduced. It closes off flow to lower-priority subsystems until adequate pressure is restored.
Why the other options are wrong
- A. A sequence valve controls the order of operation within a single system (e.g., doors before gear), not priority between systems.
- B. A pressure-reducing valve lowers pressure for a specific subsystem, but does not prioritize flow allocation during low pressure.
- C. A power transfer unit transfers hydraulic power between two independent systems, not within one system's subsystems.
Priority Valve
A valve that automatically shuts off flow to non-essential hydraulic subsystems when system pressure drops, ensuring essential systems (like flight controls) retain adequate flow.
- Protects essential systems during low pressure/flow conditions
- Common in systems shared by flight controls and landing gear/flaps
- Reopens automatically once pressure is restored
Memory trick: Priority valve = 'VIP line' — flight controls cut to the front when pressure is low.