Definition
A one-way check valve consisting of a thin, flexible flap (the reed) that opens under pressure differential to allow flow in one direction and closes against a seat to block flow in the opposite direction. In aircraft systems, reed valves are commonly found in pneumatic and vacuum systems, small two-stroke engines, and some pump assemblies.
Plain English
A simple flap-style valve that lets air or gas flow one way only. Pressure pushes the flap open; when the pressure drops or reverses, the flap snaps shut against its seat and blocks backflow.
Context Anchor
Seen in aircraft maintenance descriptions of pumps, compressors, vacuum systems, air systems, and some fluid systems where flow must move in only one direction.
Derivation
Named after the reed in a musical instrument like a clarinet or harmonica — a thin strip that vibrates and flexes under airflow. The valve works the same way: a thin flexible flap that bends to let flow through, then springs back to seal.
Why Pilots Care
If a reed valve sticks open or breaks, the system loses its one-way control — backflow occurs, pressure can't build, and the affected system (vacuum, pneumatic, or fuel/air in a small engine) stops working correctly.
Analogy
A reed valve works like a light flap over a small hole: push from one side and it lifts open; push from the other side and it seals shut.
Intuition Check
Do not picture a round hand-operated valve with a knob. A reed valve works automatically because a thin strip bends with pressure.
Example Sentence 1
The technician inspected the reed valve for cracks or warping, since a damaged reed would let air leak back through the pump.
Example Sentence 2
In the two-stroke engine, the reed valve opens during the intake stroke to admit the air-fuel mixture.