Difference between revisions of "Poppet valve"

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m (New page: right|thumb|175px|Poppet valve & components A '''poppet valve''' is a valve consisting of a hole, usually round or oval, and a tapered plug, usually a disk sh...)
 
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==Etymology==
==Etymology==
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 ''poupe''. The use of the word ''poppet'' to describe a valve comes from the same word applied to [[marionette]]s, which &ndash; like the poppet valve &ndash; move bodily in response to remote motion transmitted linearly.<ref>[http://www.merriam-webster.com/dictionary/poppet '''Poppet''' at Merriam-Webster]</ref><ref>[http://www.merriam-webster.com/dictionary/puppet '''Puppet''' at Merriam-Webster]</ref> In the past, "puppet valve" was a synonym for ''poppet valve'';<ref>[http://www.websters-online-dictionary.org/Pu/Puppet+valve.html '''Puppet valve''' from 1913 Webster's dictionary]</ref><ref>[http://patimg1.uspto.gov/.piw?Docid=00339809&homeurl=http%3A%2F%2Fpatft.uspto.gov%2Fnetacgi%2Fnph-Parser%3FSect1%3DPTO1%2526Sect2%3DHITOFF%2526d%3DPALL%2526p%3D1%2526u%3D%25252Fnetahtml%25252FPTO%25252Fsrchnum.htm%2526r%3D1%2526f%3DG%2526l%3D50%2526s1%3D0339809.PN.%2526OS%3DPN%2F0339809%2526RS%3DPN%2F0339809&PageNum=&Rtype=&SectionNum=&idkey=NONE&Input=View+first+page U.S. Patent No. 339809, "Puppet Valve", issued April 13, 1886]</ref> however, this usage of "puppet" is now obsolete.
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 ''poupe''. The use of the word ''poppet'' to describe a valve comes from the same word applied to [[marionette]]s, which &ndash; like the poppet valve &ndash; move bodily in response to remote motion transmitted linearly.<ref>[http://www.merriam-webster.com/dictionary/poppet '''Poppet''' at Merriam-Webster]</ref><ref>[http://www.merriam-webster.com/dictionary/puppet '''Puppet''' at Merriam-Webster]</ref> In the past, "puppet valve" was a synonym for ''poppet valve'';<ref>[http://www.websters-online-dictionary.org/Pu/Puppet+valve.html '''Puppet valve''' from 1913 Webster's dictionary]</ref><ref>[http://patimg1.uspto.gov/.piw?Docid=00339809&homeurl=http%3A%2F%2Fpatft.uspto.gov%2Fnetacgi%2Fnph-Parser%3FSect1%3DPTO1%2526Sect2%3DHITOFF%2526d%3DPALL%2526p%3D1%2526u%3D%25252Fnetahtml%25252FPTO%25252Fsrchnum.htm%2526r%3D1%2526f%3DG%2526l%3D50%2526s1%3D0339809.PN.%2526OS%3DPN%2F0339809%2526RS%3DPN%2F0339809&PageNum=&Rtype=&SectionNum=&idkey=NONE&Input=View+first+page U.S. Patent No. 339809, "Puppet Valve", issued April 13, 1886]</ref> however, this usage of "puppet" is now obsolete.


==Operation==
==Operation==
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==Internal combustion engine==
==Internal combustion engine==
[[Image:Four stroke engine diagram.jpg|thumbnail|right|175px|Components of a typical, [[four stroke cycle]], DOHC piston engine:<br>(E) Exhaust [[camshaft]],<br>(I) Intake camshaft,<br>(S) [[Spark plug]],<br>(V) Valves,<br>(P) [[Piston]],<br>(R) [[Connecting rod]],<br>(C) [[Crankshaft]],<br>(W) Water jacket for coolant flow.]]
[[Image:Four stroke engine diagram.jpg|thumbnail|right|175px|Components of a typical, [[four stroke cycle]], DOHC piston engine:<br>(E) Exhaust [[camshaft]],<br>(I) Intake camshaft,<br>(S) [[Spark plug]],<br>(V) Valves,<br>(P) [[Piston]],<br>(R) [[Connecting rod]],<br>(C) [[Crankshaft]],<br>(W) Water jacket for coolant flow.]]
''Poppet valves'' are used in most [[piston engine]]s to open and close the intake and exhaust [[cylinder head porting|ports]] in the [[cylinder head]]. The valve is usually a flat disk of metal with a long rod known as the ''valve stem'' out one end. The stem is used to push down on the valve and open it, with a spring generally used to close it when the stem is not being pushed on. [[Desmodromic valve]]s are closed by positive mechanical action instead of by a spring, and are used in some high speed [[motorcycle]] and [[auto racing]] engines, eliminating '[[valve float]]' at high [[RPM]].
''Poppet valves'' are used in most [[piston engine]]s to open and close the intake and exhaust [[cylinder head porting|ports]] in the [[cylinder head]]. The valve is usually a flat disk of metal with a long rod known as the ''valve stem'' out one end. The stem is used to push down on the valve and open it, with a spring generally used to close it when the stem is not being pushed on. [[Desmodromic valve]]s are closed by positive mechanical action instead of by a spring, and are used in some high speed [[motorcycle]] and auto racing engines, eliminating '[[valve float]]' at high [[RPM]].


For certain applications the valve stem and disk are made of different steel [[alloy]]s, or the valve stems may be hollow and filled with [[sodium]] to improve [[heat]] transport and transfer.
For certain applications the valve stem and disk are made of different steel [[alloy]]s, or the valve stems may be hollow and filled with sodium to improve [[heat]] transport and transfer.


The engine normally operates the valves by pushing on the stems with [[cam]]s and [[Tappet|Cam follower]]s. The shape and position of the cam determines the valve lift and when and how quickly (or slowly) the valve is opened. The cams are normally placed on a fixed [[camshaft]] which is then geared to the [[crankshaft]], running at half crankshaft speed in a [[four stroke cycle|four-stroke]] engine. On high performance engines (e.g., [[Ferrari]] cars), the camshaft is movable and the cams have a varying height, so by axially moving the camshaft in relation with the engine [[RPM]], also the valve lift varies. See [[variable valve timing]].
The engine normally operates the valves by pushing on the stems with [[cam]]s and [[Tappet|Cam follower]]s. The shape and position of the cam determines the valve lift and when and how quickly (or slowly) the valve is opened. The cams are normally placed on a fixed [[camshaft]] which is then geared to the [[crankshaft]], running at half crankshaft speed in a [[four stroke cycle|four-stroke]] engine. On high performance engines (e.g., [[Ferrari]] cars), the camshaft is movable and the cams have a varying height, so by axially moving the camshaft in relation with the engine [[RPM]], also the valve lift varies. See [[variable valve timing]].
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===Valve wear===
===Valve wear===
In the early days of engine building, the poppet valve was a major problem. [[Metallurgy]] was not what it is today, and the rapid opening and closing of the valves against the cylinder heads led to rapid wear. They would need to be re-ground every two years or so, in an expensive and time consuming process known as a ''[[valve job]]''. Adding [[tetra-ethyl lead]] to the [[petrol]] reduced this problem to some degree as the lead would coat the valve seats, in effect lubricating the metal.  Valve seats made of improved alloys such as [[stellite]] have generally made this problem disappear completely and made [[Leaded gasoline|leaded fuel]] unnecessary.
In the early days of engine building, the poppet valve was a major problem. Metallurgy was not what it is today, and the rapid opening and closing of the valves against the cylinder heads led to rapid wear. They would need to be re-ground every two years or so, in an expensive and time consuming process known as a ''[[valve job]]''. Adding [[tetra-ethyl lead]] to the [[petrol]] reduced this problem to some degree as the lead would coat the valve seats, in effect lubricating the metal.  Valve seats made of improved alloys such as stellite have generally made this problem disappear completely and made leaded fuel unnecessary.