page_title: Poppet valve
section_title: Steam engine
hierarchical_section_title: Poppet valve / Operation / Steam engine
caption_attribution_description: Français&#160;: La 231 E 41 à St-Pierre-Des-Corps le 29/08/1982.
context_page_description: A poppet valve is a valve typically used to control the timing and quantity of gas or vapor flow into an engine.
  It consists of a hole, usually round or oval, and a tapered plug, usually a disk shape on the end of a shaft also called a valve stem. The portion of the hole where the plug meets with it is called the "seat" or "valve seat". The shaft guides the plug portion by sliding through a valve guide. In exhaust applications a pressure differential helps to seal the valve and in intake valves a pressure differential helps open it. The poppet valve was most likely invented in 1833 by E.A.G. Young of the Newcastle and Frenchtown Railroad. Young patented his idea, but the Patent Office fire of 1836 destroyed all records of it.
context_section_description: James Watt was using poppet valves to control the flow of steam into the cylinders of his beam engines in the 1770s. A sectional illustration of Watt's beam engine of 1774 using the device is found in Thurston 1878:98, and Lardner (1840) provides an illustrated description of Watt's use of the poppet valve.
  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. 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. 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.
  Poppet valves have been used on steam locomotives, often in conjunction with 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 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 T1 duplex locomotives, although the valves commonly failed because the locomotives were commonly operated in excess of 160 km/h (100 mph), and the valves were not meant for the stresses of such speeds. The poppet valves also gave the locomotive a distinctive "chuffing" sound.
caption: Oscillating poppet valve on one of Chapelon's rebuilt 4-6-2 locomotives.
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