Definition
A poppet-type valve in the cylinder head of a reciprocating engine that opens during the exhaust stroke to allow burned combustion gases to leave the cylinder, then closes to seal the cylinder during the intake, compression, and power strokes. Aircraft engine exhaust valves operate at very high temperatures and are often hollow and partially filled with metallic sodium, which liquefies in flight and transfers heat from the valve head to the stem.
Plain English
A small valve at the top of each engine cylinder that opens to let the hot, used gases escape after each burn, then closes again so the next mixture can be compressed and burned.
Context Anchor
Seen in aircraft engine descriptions, maintenance discussions, compression checks, and troubleshooting for rough running or loss of power.
Derivation
From Latin exhaurire, meaning 'to draw out' or 'empty'. The exhaust valve is literally the door through which the engine empties its cylinders.
Why Pilots Care
Ensuring the exhaust valve functions correctly prevents engine damage and maintains power output during flight.
Analogy
Think of it like a small automatic door at the exit of a room. It opens at the right time to let the used air out, then closes so the next event can happen in a sealed space.
Intuition Check
Do not confuse the exhaust valve with the exhaust pipe or muffler. The exhaust valve is inside the engine cylinder and controls when burned gases are allowed to leave.
Example Sentence 1
During the exhaust stroke, the exhaust valve opens and the piston pushes the burned gases out of the cylinder.
Example Sentence 2
A stuck exhaust valve can cause a loss of power and rough running in the aircraft engine.