CHAPTER VII. 

 THE VALVE-GEAR. 



.HE 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 trac- 

 tion 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 

 invented 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 certain intervals. 

 Consequently, the economy of a steam engine depends 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. If the valve be allowed 



