^ Jacques Mouchly, Valve and Valve Gear for Locomotives and Other Engines, U.S.The steam engine explained and illustrated. A History of the Growth of the Steam Engine. Archived (PDF) from the original on Octo. ^ 'A Handy Guide to Clinton Engines' (PDF).Archived from the original on 18 March 2018. ^ ' Puppet valve from 1913 Webster's dictionary'.North Chelmsford, MA: Courier Corporation. Dyke (1921), Dyke's Automobile and Gasoline Encyclopedia, St. The poppet valves also gave the locomotive a distinctive 'chuffing' sound. The poppet valve was also used on the American Pennsylvania Railroad's T1duplex 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. Such a condition occurs when changing gear. Worn valve guides and/or defective oil seals can often be diagnosed by a puff of blue smoke from the exhaust pipe on releasing the accelerator pedal after allowing the engine to overrun, when there is high manifold vacuum. Because the valve stem extends into lubrication in the cam chamber, it must be sealed against blow-by to prevent cylinder gases from escaping into the crankcase, even though the stem to valve clearance is very small, typically 0.04-0.06 mm, so a rubber lip-type seal is used to ensure that excessive oil is not drawn in from the crankcase on the induction stroke, and that exhaust gas does not enter the crankcase on the exhaust stroke. Although a better heat conductor, an aluminium cylinder head requires steel valve seat inserts, where a cast iron cylinder head would often have employed integral valve seats in the past. For certain applications the valve stem and disk are made of different steel alloys, or the valve stem may be hollow and filled with sodium to improve heat transport and transfer.
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