CHAPTER VII 



THE VALVE-GEAR 



THE mechanism that operates the valve of an engine 

 is known as the "valve-gear." On stationary or 

 portable engines, which are only required to run 

 in one direction, the valve gear consists simply of an 

 eccentric on the crank shaft (to which the valve stem is 

 connected by means of the eccentric-rod), and a guide to 

 keep the valve-stem in alignment. As traction engines 

 must be run in both directions, a reversing- valve gear is 

 required, which necessarily renders the valve gear more 

 complicated. There have been numerous mechanisms in- 

 vented for this purpose, but most traction engines are 

 equipped with either the "link" or the Woolf reverse, as 

 these are almost the only ones that have withstood the test 

 of time. 



It is apparent, that, in order to use steam econom- 

 ically, it must be allowed to pass in and out of the cylinder 

 at precisely the right moments, and during 1 certain inter- 

 vals. Consequently, the economy of a steam engine de- 

 pends almost entirely upon the valve-gear, which should, 

 therefore, be kept in good repair. The ease with which 

 the valve is moved, depends largely upon its lubrication. 



