128 



SCIENCE OF THRESHING. 



with the shaft center. Tt therefore follows that this 

 center, O, describes a circle around the shaft, and the 

 diameter, W ', of this circle is the throw of the eccen- 

 tric. The eccentric strap, 10, which surrounds it, and 

 the eccentric rod, u, will consequently travel back 

 and forth a distance equal to this diameter. The 

 radius of this circle is the radius of the eccentric. 

 The eccentric is in effect a crank and reciprocates the 

 valve stem and valve. The connection between the 

 eccentric and valve stem may be made in a number of 

 ways. 



THE SLIDE VALVE. 



The D-slide valve is the most common of the 

 valves used to distribute steam in the engine cylinder. 

 A section of such valve is shown in the figure in its 

 central position, pp are the steam ports, oo the 

 bridges, E the exhaust port, ST the valve seat. The 

 flanges of the valve, ab and cd, are seen to be wider 

 than the ports which they cover. Of this extra width 

 the parts ee are called the outside lap, and the parts 

 // the inside lap. F is the valve stem connecting 

 with the eccentric. 



As the motion of the valve is given by the eccen- 



