WordNet records no synonym and no antonym for valve. It is the only member of each of its synsets, 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 structure in a hollow organ (like the heart) with a flap to insure one-way flow of fluid through it
device in a brass wind instrument for varying the length of the air column to alter the pitch of a tone
control consisting of a mechanical device for controlling the flow of a fluid
the entire one-piece shell of a snail and certain other molluscs
one of the paired hinged shells of certain molluscs and of brachiopods
Synonyms, antonyms and the broader and narrower relations for valve come from Princeton University’s WordNet. Full sources and licences.