Definition
The hardened, ring-shaped surfaces in the cylinder head of a reciprocating aircraft engine against which the intake and exhaust valves close. When a valve is shut, its face presses firmly against the matching valve seat to form a gas-tight seal, preventing the loss of compression and combustion gases from the cylinder.
Plain English
The metal rings inside an engine cylinder that the valves press against when they close, sealing the cylinder so combustion pressure doesn't leak out.
Context Anchor
Seen in aircraft piston engine maintenance, especially during cylinder inspection, valve work, and troubleshooting for rough running or low power.
Derivation
From 'seat,' meaning the place where something rests or sits firmly. The valve 'sits' on its seat each time it closes, just as a door rests against its frame to seal an opening.
Why Pilots Care
Worn or damaged valve seats can cause loss of engine compression, leading to power loss or engine failure.
Analogy
Think of a pressure cooker lid pressing into the rim of the pot. The rim is the seat; if the rim is dented or rough, steam escapes. Same idea inside a cylinder.
Intuition Check
Do not picture passenger seats. Valve seats are not places for people; they are the sealing surfaces where engine valves close.
Example Sentence 1
During the cylinder overhaul, the mechanic ground the valve seats to restore a clean sealing surface.
Example Sentence 2
The mechanic replaced the valve seats after finding cracks during the cylinder inspection.