Tappet
Tappet , noun
(Machinery) A lever or projection moved by some other piece, as a cam, or intended to tap or touch something else, with a view to produce change or regulate motion. — G. Francis
Collocations (1)
Tappet motion , a valve motion worked by tappets from a reciprocating part, without an eccentric or cam, -- used in steam pumps, etc.