Poppet valve
WordNet
noun
(1) A mushroom-shaped valve that rises perpendicular from its seat; commonly used in internal-combustion engines
WiktionaryText
Noun
- A valve (as in an internal combustion engine) which consists of a sliding shaft with a disk on the end (the disk being shaped to alternately plug and unplug a matching port) and which is operated by springs and possibly cams interacting with the shaft.