FAA Aviation Mechanic Airframe (AMA)Hydraulic and Pneumatic SystemsHard
On a transport category aircraft with two independent hydraulic systems, a technician learns that one system can be used to power a pump that pressurizes fluid in the other system without any fluid mixing between the two systems. What component performs this function?
- APriority valve
- BSequence valve
- CSelector valve
- DPower transfer unit (PTU)
Show answer & explanationAnswer & explanation
Correct answer: D. Power transfer unit (PTU)
A power transfer unit (PTU) uses fluid pressure/flow from one hydraulic system to drive a hydraulic motor that, in turn, drives a pump in a second, completely separate hydraulic system, transferring power without mixing the two fluids. This is used for redundancy when one system's pump has failed.
Why the other options are wrong
- A. A priority valve allocates fluid within a single system to essential functions, not across systems.
- B. Sequence valves control the timing order of actuators within a system.
- C. Selector valves direct flow to different actuators within one system.
Power Transfer Unit (PTU)
A device that transfers hydraulic power from one system to another via a motor-pump combination, without mixing the fluids of the two systems.
- Motor side driven by System A fluid
- Pump side pressurizes System B fluid
- Provides redundancy if one system's pump fails
Memory trick: PTU is a matchmaker pump — energy crosses, fluid never mixes.