CHAPTER LX 

 THE STEAM ENGINE 



Mounting. Steam engines used in agricultural work are 

 usually mounted directly upon the boiler, making with the 

 boiler a complete power plant, as in the case of a portable or 

 traction engine. An engine mounted upon a masonry foun- 

 dation is said to be a stationary engine. All such engines do 

 not differ essentially in construction. 



Principle. The steam engine consists fundamentally of 

 a cylinder containing a close-fitting piston. This piston is 

 connected through a piston rod to a crosshead and in turn 

 through a connecting rod to a crank on the engine shaft. The 

 crosshead is operated between guides. The steam is admit- 

 ted at the ends of the cylinder through valves contained 

 within the steam chest. The proper 

 action is given to the valves by an 

 eccentric on the engine shaft, con- 

 nected either to the valve rod, which 

 extends into the steam chest in the 

 case of a nonreversing engine, or to 

 the reversing mechanism on a revers- 

 ing engine. As steam enters the 

 cylinder it pushes on the piston and 

 causes it to move. After the piston 

 has completed a part of the stroke, the valve closes, but the 

 expanding pressure of the steam in the cylinder enables it to 

 perform additional work on the piston. At the end of the 

 stroke the steam is released, and the pressure is applied to the 

 opposite side of the piston. This is all done automatically 



Fig. 247. A sectional view 

 of the cylinder and steam 

 chest of a simple engine. 



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