WordNet records no synonym and no antonym for butterfly valve. It is the only member of its synset, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
a valve in a carburetor that consists of a disc that turns and acts as a throttle
Synonyms, antonyms and the broader and narrower relations for butterfly valve come from Princeton University’s WordNet. Full sources and licences.