FAA Commercial Pilot Airplane (CAX)Aircraft SystemsHard
A hydraulically actuated retractable landing gear system includes a valve that opens automatically to relieve excess pressure caused by thermal expansion of fluid trapped in the actuator lines after the gear is locked. What is this valve called?
- ASequence valve
- BThermal relief valve
- COrifice check valve
- DPriority valve
Show answer & explanationAnswer & explanation
Correct answer: B. Thermal relief valve
A thermal relief valve prevents damage from pressure buildup caused by fluid expansion in a closed hydraulic line (e.g., due to temperature increase after the gear is locked). Sequence valves control the order of gear/door movement, and priority valves control the order of system function priority, neither of which addresses thermal expansion.
Why the other options are wrong
- A. Sequence valves control the timing order of gear and door actuation, not pressure relief.
- C. An orifice check valve controls flow rate/direction, not thermal pressure relief.
- D. Priority valves ensure one function gets hydraulic pressure before another.
Hydraulic Thermal Relief Valve
A valve that opens to release excess pressure caused by thermal expansion of fluid trapped in a closed hydraulic line, protecting components from damage.
- Protects trapped fluid lines from heat-induced pressure buildup
- Distinct from sequence and priority valves
- Common wherever fluid can be isolated in a closed line, e.g., locked gear actuators
Memory trick: Trapped fluid heats up and needs a release valve, not a sequencer.