A valve opened by the action of a cam and closed by a spring.
When open, the sealing surface of the valve is moved away from a seat. When closed, the sealing surface contacts the seat to shut off the flow. Poppet valves are used extensively as pneumatic controls and as intake and exhaust valves in most internal combustion engines.
The clearance between cam, tappet and valve must be slowly taken up and valve slowly lifted, at first, if noise and wear is to be avoided. For the same reasons the valve cannot be closed abruptly, else it will ′bounce′ on its seat.