Principles of naval engineering - Historic Naval Ships Association

Chapter 1-THE DEVELOPMENT OF NAVAL SHIPSWORKING BEAMCHAINCHAINWATER INJECTION VALVEPUMP RODSTEAM ADMISSION VALVEAUTOMATIC VALVEGEARDRAIN LINE-^t^T'jipw*^-:INJECTIONWATER PUMP"VERTICALLIFTPUMPFigure 1-1.— The Newcomen engine.147.1After the steam has forced the piston to itstop position, the steam valve is shut and a jet ofcold water enters the cylinder, condensing thesteam and creating a partial vacuum. Atmosphericpressure then causes the down stroke(work stroke) of the piston.As the piston comes down, the working beamis pulled down on the cylinder side. As the beamrises on the pump side, the pump rod also risesand water is lifted upward. As soon as the pressurein the cylinder equals atmospheric pressure,an escape valve in the bottom of the cylinderopens and the condensate is dischargedthrough a drain line into a sump.The use of automatic valve gear to controlthe admission of steam and the admission ofcold water made the Newcomen engine the firstself-acting mechanism since the invention of theclock. In the earliest versions of the Newcomenengine, it is most likely that the admission ofsteam and cold water was controlled by themanual operation of taps rather than by automaticgear. The origin of the automatic gearis a matter of some dispute. One story has itthat a young boy named Humphrey Potter, whowas hired to turn the taps, invented the valvegear so that he could go fishing while the enginetended itself. This story, although persistent,is considered "absurd" by some serious historiansof the steam engine,^James Watt, although often given credit forinventing the steam engine, did not even beginworking on steam engines until some 50 years^See, for example, Eugene S. Ferguson, "The Originsof the Steam Engine," Scientific American . January1964, pp. 98-107.