Definition
A pressure-limiting device in a hydraulic or pneumatic system that opens automatically when fluid pressure exceeds a preset value, venting fluid back to the reservoir or to a lower-pressure line, then reseating once pressure drops to a safe level. In landing gear hydraulic systems it protects pumps, lines, seals, and actuators from damage caused by over-pressurization.
Plain English
A safety valve that lets pressure escape if it gets too high, then closes again once pressure is back to normal. It stops the system from being damaged by too much force building up inside it.
Context Anchor
Seen in landing gear system discussions, especially hydraulic gear systems where pressure is used to extend or retract the gear.
Derivation
From 'relief' (to ease or lessen) and 'valve' (a device that controls flow). The name describes exactly what it does: it relieves excess pressure by opening a flow path.
Why Pilots Care
Protects the hydraulic system from over-pressure damage, ensuring reliable landing-gear operation during every takeoff and landing.
Analogy
Like the small valve on a pressure cooker that pops open to let steam escape when pressure inside gets too high.
Intuition Check
Relief does not mean comfort here. It means releasing excess pressure from a system. A relief valve is usually automatic; the pilot does not normally open it by hand.
Example Sentence 1
When the landing gear reached the fully retracted position, the hydraulic relief valve opened to bleed off excess pressure and protect the system.
Example Sentence 2
During the preflight walk-around the mechanic verified that the landing-gear relief valve was free of leaks and properly seated.