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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.
A desmodromic valve is a reciprocating engine poppet valve that is positively closed by a cam and leverage system, rather than by a more conventional spring. The valves in a typical four-stroke engine allow the air/fuel mixture into the cylinder at the beginning of the cycle and exhaust spent gases at the end of the cycle.
Poppet valve, commonly used in piston engines to regulate the fuel mixture intake and exhaust; Pressure-balanced valve; Pressure reducing valve, regulates the pressure of a fluid; Safety valve or relief valve: operates automatically at a set pressure to correct a potentially dangerous situation, typically over-pressure; Sampling valve
Most modern engines use poppet valves, although sleeve valves, slide valves and rotary valves have also been used at times. Poppet valves are typically opened by the camshaft lobe or rocker arm, and closed by a coiled spring called a valve spring. Valve float occurs when the valve spring is unable to control the inertia of the valvetrain at ...
The poppet valves are controlled by the rotating camshaft at the top. High pressure steam enters, red, and exhausts, yellow. The uniflow type of steam engine uses steam that flows in one direction only in each half of the cylinder. Thermal efficiency is increased by having a temperature gradient along the cylinder. Steam always enters at the ...
With traditional fixed valve timing, an engine will have a period of "valve overlap" at the end of the exhaust stroke, when both the intake and exhaust valves are open. The intake valve is opened before the exhaust gases have completely left the cylinder, and their considerable velocity assists in drawing in the fresh charge. Engine designers ...
The upper part of the valve stem, within the rocker box, is lubricated by oil. If this oil travels unchecked along the valve stem, engine HC emissions will become excessive. To control this, an elastomeric seal is fitted over the top of the valve guide. These may wear or stiffen with age, so are usually replaced whenever valves are removed for ...
A camless or free-valve piston engine is an engine that has poppet valves operated by means of electromagnetic, hydraulic, or pneumatic [1] actuators instead of conventional cams. Actuators can be used to both open and close valves, or to open valves closed by springs or other means.