Definition
A mushroom-shaped valve used to control the flow of gases into and out of the cylinder of a reciprocating engine. It consists of a circular head that seals against a matching seat in the cylinder, and a long stem that rides in a guide. The valve is opened by a cam pushing on the stem and closed by one or more springs that hold the head firmly against the seat.
Plain English
A spring-loaded valve shaped like a mushroom that opens and closes the intake and exhaust openings in an engine cylinder. A cam pushes it open; a spring snaps it shut.
Context Anchor
Seen in aircraft piston-engine descriptions, engine inspections, and discussions of intake and exhaust valve operation.
Derivation
From the old English word 'poppet,' meaning a small figure or doll that pops up and down. The name reflects the way the valve pops open and shut as the cam rotates.
Why Pilots Care
Proper sealing and timing are essential for compression, power output, and preventing valve damage or engine failure.
Analogy
A poppet valve works like a sink drain stopper: when it sits down, it seals the opening; when it lifts up, flow can pass through.
Intuition Check
Do not think of a poppet valve as a valve that makes a popping sound. The important idea is that it lifts off its seat to open and sits back down to seal.
Example Sentence 1
The mechanic found a burned exhaust poppet valve during the compression check on the number three cylinder.
Example Sentence 2
Each poppet valve opens when its cam lobe pushes the lifter and rocker arm.