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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.
Valves can be categorized also based on their function: Check valve or non-return valve, allows the fluid to pass in one direction only; Flow control valve, to maintain and control a variable flow rate through the valve; Poppet valve, commonly used in piston engines to regulate the fuel mixture intake and exhaust; Pressure-balanced valve
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.
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.
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 ...