7 SCIENCE OF SUCCESSFUL THRESHING 



to run dry, the valve gear is subjected to an immense amount 

 of unnecessary work, which soon wears it, so that the valve 

 does not move as it should,, and the engine becomes wasteful 

 in its use of steam. The valve should be well lubricated at 

 all times, the wearing parts of the valve-gear should be 

 oiled frequently and every precaution taken to keep the valve- 

 gear in first class condition. The wear should be taken up 

 as fast as it appears so that the parts are not allowed to 

 pound. 



The Woolf Valve-Gear. The Woolf valve-gear possesses 

 advantages over the other devices used for reversing trac- 

 tion engines, which entitle it to rank as the most popular and 

 satisfactory means for this purpose known at the present 

 time. It is very simple, consisting of a single eccentric, the 

 ''strap'' of which is extended to form an arm; to the end 

 of this arm is pivoted a block, which slides in a guide con- 

 nected to the hand lever and pivoted in such a way that the 

 angle of the block's path depends upon the position of the 

 hand lever; the eccentric rod transmits the motion from the 

 eccentric arm, (to which it is connected), to the valve stem 

 through a rocker arm or guided "slide." It will be seen 

 that the angle of the "block guide" determines the amount 

 of travel of the valve. By placing the reverse lever at or 

 near the center of the quadrant, the reverse gear acts as an 

 efficient brake in controlling the engine when descending 

 hills, or at any time when it is desirable to suddenly check 

 the speed of the engine. This reverse allows of "hooking 



