Definition
A fitting or device installed in a fluid line that intentionally limits the rate of flow in one or both directions. Restrictors are used in hydraulic and pneumatic systems to control the speed at which an actuator moves, to slow the operation of a component, or to balance pressure between two sides of a system.
Plain English
A small part placed inside a line carrying fluid or air that slows the flow down on purpose, so something connected to it moves or reacts more gently.
Context Anchor
Seen in aircraft maintenance descriptions of hydraulic, fuel, pneumatic, and instrument systems, especially where flow must be slowed or controlled.
Derivation
From the Latin 'restringere', meaning 'to bind back' or 'hold back'. The aviation use keeps that idea directly: the device holds back the flow rather than stopping it completely.
Why Pilots Care
Restrictors keep system components from slamming or operating too quickly, which protects the airframe and gives predictable handling of gear, flaps, and other moving parts.
Analogy
A restrictor works like a faucet opened only partway: the pipe may be full, but the small opening controls how fast the liquid can pass.
Intuition Check
Do not think of a restrictor as an accidental blockage. A restrictor is an intended, correctly sized limit; a blockage is unwanted and can cause a malfunction.
Example Sentence 1
A restrictor in the landing gear up-line slows the gear retraction so it does not slam into the wheel well.
Example Sentence 2
Fuel system restrictors prevent excessive pressure from reaching the engine-driven pump.