<P> The word poppet shares etymology with "puppet": it is from the Middle English popet ("youth" or "doll"), from Middle French poupette, which is a diminutive of poupée . The use of the word poppet to describe a valve comes from the same word applied to marionettes, which--like the poppet valve--move bodily in response to remote motion transmitted linearly . In the past, "puppet valve" was a synonym for poppet valve; however, this usage of "puppet" is now obsolete . The valve stem moves up and down inside the passage called guide, which is fitted in the engine - block . the head of the valve called valve face, is generally grounded to 45 degrees angle, so as to fit properly on the value seat in the block and prevent leakage </P> <P> The poppet valve is fundamentally different from slide and oscillating valves; instead of sliding or rocking over a seat to uncover a port, the poppet valve lifts from the seat with a movement perpendicular to the plane of the port . The main advantage of the poppet valve is that it has no movement on the seat, thus requiring no lubrication . </P> <P> In most cases it is beneficial to have a "balanced poppet" in a direct - acting valve . Less force is needed to move the poppet because all forces on the poppet are nullified by equal and opposite forces . The solenoid coil has to counteract only the spring force </P> <P> Poppet valves are used in many industrial processes, from controlling the flow of milk to isolating sterile air in the semiconductor industry . However, they are most well known for their use in internal combustion and steam engines, as described below . </P>

Types of valve arrangement in an internal combustion engine