. The railroad and engineering journal . t are so arranged thatthe steam-ports, through which steam is admitted to the-cylinder, are each open during a portion only of the stroke ofthe piston. When it has moved through a part of its stroke,the port through which steam is entering the cylinder is closed,without allowing the steam which has been admitted to thecylinder to escape, until the piston has nearly reached the endof its stroke. Consequently when the steam is thus enclosed,or cut-olT as it is termed, its expansive action continues toexert a diminishing pressure against the piston until t
. The railroad and engineering journal . t are so arranged thatthe steam-ports, through which steam is admitted to the-cylinder, are each open during a portion only of the stroke ofthe piston. When it has moved through a part of its stroke,the port through which steam is entering the cylinder is closed,without allowing the steam which has been admitted to thecylinder to escape, until the piston has nearly reached the endof its stroke. Consequently when the steam is thus enclosed,or cut-olT as it is termed, its expansive action continues toexert a diminishing pressure against the piston until the exhaustport is opened. Thus, in fig. 20, it will be seen that the valvehas nearly closed the steam-port, although the piston has notyet reached the end of its stroke. Fig. 34 shows the valve onan enlarged scale in the position it occupies when the steam-port c is first closed ; and in fig. 35 the valve is representedafter it has moved far enough to begin to open communicationfrom the steam-port c 10 the exhaust-port v as indicated by. the dart d. While the valve is moving from the position inwhich it is shown in fig. 34 to that represented in fig. 35, it isevident that the steam-port - is covered by the valve, andtherefore during that period the steam is confined in the frontend of the cylinder and expands as the piston advances. Itthus exerts a pressure on the piston after the steam-port isclosed. As the piston advances, and the space or volumeoccupied by the steam in the cylinder is increased, the pressureof the steam is reduced as was explained in answer to ques-tion 42. Question 81. How can we know how mmh pivssuir is the steam during expansion ? Answer. As long ago as the year 1662 Robert Boyle, fromexperiments ton. Iiiml ilie siiring of air, discovered the lawthat • thepro^u, . ^-as ,it a temperotiiye varies inversely .I ihes ; or, as stated in answer to question 42, lh,\ .;., ;«, ,,.., ,v proportional to eaeh other. Thus,suppose we have a
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectrailroa, bookyear1887
