The Collaborative International Dictionary
Tappet motion
Tappet \Tap"pet\, n. (Mach.)
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.
Tappet motion, a valve motion worked by tappets from a reciprocating part, without an eccentric or cam, -- used in steam pumps, etc.