Search results
Results From The WOW.Com Content Network
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.
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 ...
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 ...
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. In a conventional ...
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 ...
Poppet valve and sleeve valve: commonly used in piston engines to regulate the fuel mixture intake and exhaust; Pressure regulator or pressure reducing valve (PRV): reduces pressure to a preset level downstream of the valve; Pressure sustaining valve, or back-pressure regulator: maintains pressure at a preset level upstream of the valve
In August 1926, the London, Midland and Scottish Railway equipped four-cylinder 4-6-0 locomotive no. 5908 of the Claughton Class with Caprotti valve gear and poppet valves. . Following trials, nine more were rebuilt in 1928 with Caprotti valve gear, poppet valves and larger boilers, and also in 1928 ten others of the same class were given the larger boiler but retained the Walschaerts valve ...
The poppet valve's previous problems with sealing and wear had been remedied by the use of better materials and the inertia problems with the use of large valves were reduced by using several smaller valves instead, giving increased flow area and reduced mass, and the exhaust valve hot spot by Sodium-cooled valves. Up to that point, the single ...