208 



GENERAL SCIENCE 



is attached, and of course many changes have been made 

 in the mechanism of the engine itself, but there has been 

 no change in principle. 



The operation of a double-acting steam engine can be 

 understood from the diagram shown in the illustration. 

 The steam generated by the fire, F, in the boiler, B, passes 

 through the pipe, P, into the steam chest, C, and thence 

 through the passage, 0, into the cylinder, N, where its 



THE PARTS or A STEAM ENGINE 



pressure forces the piston, 5, to the left. It can be seen 

 from the diagram that, as the driving rod, R, moves 

 toward the left, the eccentric rod, H, which controls the 

 valve, V, moves toward the right. When the piston has 

 reached the left end of its stroke, the passage O will have 

 been closed, while the passage D will have been opened, 

 thus permitting the steam to flow into the left end of the 

 cylinder, which will force the piston to the right and 

 force the spent steam on the right of the piston out 

 through the exhaust pipe, E. The eccentric rod, H, 

 moves the double valve in the steam chest, which opens 

 and closes the passages and D alternately at just the 



