Definition
A valve in the cylinder head of a reciprocating engine that opens to admit the fuel-air mixture (or air alone, in fuel-injected engines) into the cylinder during the intake stroke, and closes to seal the cylinder during compression, combustion, and exhaust.
Plain English
The door at the top of an engine cylinder that opens to let the fuel-air mixture in, then closes so the mixture can be squeezed and burned.
Context Anchor
Seen in piston-engine aircraft engine descriptions, maintenance discussions, and troubleshooting for rough running or poor power.
Derivation
Intake comes from 'in' plus 'take' — literally the place where something is taken in. Valve comes from the Latin 'valva,' meaning a leaf of a folding door. So an intake valve is the door through which the cylinder takes in its charge.
Why Pilots Care
A stuck or leaking intake valve prevents the cylinder from filling properly, causing rough running, power loss, or complete engine failure.
Analogy
Think of it like a door that opens only at the right moment to let fresh air into a room, then closes so the room can do its job without leaking.
Intuition Check
Do not confuse the intake valve with the outside air inlet on the aircraft. The intake valve is an internal engine part that controls flow into a cylinder.
Example Sentence 1
On the intake stroke, the piston moves down and the intake valve opens to draw the fuel-air mixture into the cylinder.
Example Sentence 2
During the annual inspection the mechanic checked the intake valves for signs of carbon buildup or wear.