572 



MACHINES, WORK, AND ENERGY 



683. The Modern Steam Engine. The construction and 

 operation of the modern steam engine is shown in Fig. 357. 

 The governor controls the speed of the engine by controlling 

 the rate at which the steam enters the cylinder. The governor 

 belt running from the shaft of the flywheel causes the gov- 

 ernor to revolve. As the speed increases, the heavy balls, 

 owing to centrifugal force (Art. 622), tend to swing farther 

 out, i.e., revolve in a larger circle. As they do so they force 

 the cut-off valves down, thus reducing the flow of steam. 



FIG. 357. The modern steam engine. 



As the flow of steam decreases, the force with which the 

 piston is driven becomes less and the speed of the flywheel 

 is lessened. As the speed of the flywheel becomes less, the 

 cut-off valves again rise admitting more steam. Thus the 

 speed of the engine is automatically controlled. 



After passing the governor cut-off valves, the steam enters 

 the steam chest, S-C. From the steam chest it passes through 

 the port, P, into the right-hand end of the cylinder. The 

 steam pressure then forces the piston to the left. The steam 

 in the left end of the cylinder escapes through the other port, 

 P, to the exhaust, E, whence it escapes to the air or the 

 condenser. 



