Definition
The mechanically operated intake and exhaust valves located in the cylinder head of a reciprocating (piston) aircraft engine. Each cylinder typically has one intake valve, which opens to admit the fuel-air mixture into the combustion chamber, and one exhaust valve, which opens to release burned gases after combustion. The valves are opened by pushrods and rocker arms driven by the camshaft, and are closed by valve springs. Their precise timing relative to piston position is what allows the engine to complete its intake, compression, power, and exhaust strokes correctly.
Plain English
These are the small spring-loaded doors at the top of each cylinder. One lets fresh fuel and air in, the other lets burned gases out. They open and close in time with the piston so the engine can run properly.
Context Anchor
Seen in piston-engine systems, engine inspections, compression checks, and maintenance discussions about rough running or loss of power.
Derivation
The word valve comes from the Latin valva, meaning a leaf of a folding door. That image fits well — these parts act as small doors that swing open and shut to control what enters and leaves the cylinder.
Why Pilots Care
Valve condition directly affects engine compression, power, smoothness, and safety; failure can cause loss of power or engine damage.
Analogy
Think of each cylinder as a small room where a burn happens. The intake valve is the door that lets the fresh mixture in, and the exhaust valve is the door that lets the used gases out.
Intuition Check
Do not think of these valves as cockpit knobs or fuel shutoff controls. Here, valves are internal engine parts inside each cylinder area that control gas flow during engine operation.
Example Sentence 1
During the annual inspection, a differential compression test showed air leaking past the exhaust valve in the number three cylinder.
Example Sentence 2
Proper timing of the valves in the cylinders of an aircraft reciprocating engine ensures efficient power production on every stroke.