Editing Poppet valve (section)

== Usage in steam engines ==
[[File:PuppetValve.png|right|thumb|upright|Balanced poppet valve from U.S. Patent 339,809. High pressure steam enters at ''A'' and exits at ''B''. The valve stem ''D'' moves up to open the valve discs ''C''.]]

[[James Watt]] was using poppet valves to control the flow of steam into the cylinders of his [[beam engine]]s in the 1770s. A sectional illustration of Watt's beam engine of 1774 using the device is found in Thurston 1878:98,<ref name="Thurston 1878 98">{{Cite book|last=Thurston|first=R.H.|title=A History of the Growth of the Steam Engine|year=1878|publisher=Appleton & Co.|location=New York|pages=[https://archive.org/details/cu31924031167632/page/n123 98]|url=https://archive.org/details/cu31924031167632}}</ref> and Lardner (1840) provides an illustrated description of Watt's use of the poppet valve.<ref>{{Cite book|last=Lardner|first=Dionysius|author-link=Dionysius Lardner |title=The steam engine explained and illustrated|year=1840|publisher=Taylor and Walton|location=London |pages=[https://archive.org/details/steamengineexpla00lardrich/page/189 189]–91 |url=https://archive.org/details/steamengineexpla00lardrich |url-status=live |archive-url=https://web.archive.org/web/20131004215524/http://archive.org/details/steamengineexpla00lardrich |archive-date=2013-10-04}}</ref>

When used in high-pressure applications, for example, as admission valves on steam engines, the same pressure that helps seal poppet valves also contributes significantly to the force required to open them. This has led to the development of the balanced poppet or [[double beat valve]], in which two valve plugs ride on a common stem, with the pressure on one plug largely balancing the pressure on the other.<ref>Jacques Mouchly, Valve and Valve Gear for Locomotives and Other Engines, U.S. Patent 1,824,830, issued Sept. 29, 1931.</ref><ref>Herman G. Mueller, Steam Engine Valve, U.S. Patent 1,983,803, issued Dec. 11, 1934.</ref> In these valves, the force needed to open the valve is determined by the pressure and the difference between the areas of the two valve openings. [[Frederick Ellsworth Sickels|Sickels]] patented a valve gear for double-beat poppet valves in 1842. Criticism was reported in the journal Science in 1889 of equilibrium poppet valves (called by the article the "double or balanced or American puppet valve") in use for paddle steamer engines, that by its nature it must leak 15 percent.<ref>Criticism by E.N. Dickerson in lecture to the Electric Club of New York 17/01/1889, reported by Science vol.13 No.314, Feb 8 1889 p.95 [https://www.science.org/doi/pdf/10.1126/science.ns-13.314.94 sciencemag.org]</ref>

[[File:231-E-41-d.jpg|left|thumb|upright=1.15|Oscillating poppet valve on one of Chapelon's rebuilt [[4-6-2]] locomotives]]
Poppet valves have been used on [[steam locomotive]]s, often in conjunction with [[Hugo Lentz|Lentz]] or [[Caprotti valve gear]]. British examples include:
* [[LNER Class B12]]
* [[LNER Class D49]]
* [[LNER Class P2]]
* [[LMS Stanier Class 5 4-6-0]]
* [[BR standard class 5]]
* [[BR Standard Class 8|BR standard class 8 71000 Duke of Gloucester]].

[[Sentinel Waggon Works]] used poppet valves in their steam wagons and steam locomotives. Reversing was achieved by a simple sliding [[camshaft]] system.

Many locomotives in France, particularly those rebuilt to the designs of Andre Chapelon, such as the [[SNCF 240P]], used Lentz oscillating-cam poppet valves, which were operated by the Walschaert valve gear the locomotives were already equipped with.

The poppet valve was also used on the American [[Pennsylvania Railroad]]'s [[PRR T1|T1]] [[duplex locomotive]]s, although the valves commonly failed because the locomotives were commonly operated in excess of {{Convert|160|km/h|-1|abbr=on}}, and the valves were not meant for the stresses of such speeds. The poppet valves also gave the locomotive a distinctive "chuffing" sound.

One poppet valve design was invented in 1833 by American E.A.G. Young of the [[New Castle and Frenchtown Turnpike and Railroad Company|Newcastle and Frenchtown Railroad]]. Young had patented his idea, but the [[1836 U.S. Patent Office fire|U.S. Patent Office fire of 1836]] destroyed all records of it.<ref>{{Cite book|last=White|first=John H.|title=A History of the American Locomotive|year=1979|publisher=Courier Corporation|location=North Chelmsford, MA|pages=145}}</ref>