6 4 



SCIENCE OF SUCCESSFUL THRESHING. 



the cylinders are abreast and each piston connected to a 

 separate crank; the "trunk," in which two pistons of the 

 same size are connected by an enlarged rocT or trunk, the 

 high-pressure cylinder being in the form of an annular ring 

 between the pistons, and the low-pressure at the ends of the 

 long cylinder which is the same bore throughout; and the 

 "tandem," having one cylinder behind the other, with both 

 pistons on the same rod. The latter has proved to be the 

 type best adapted for use on farm and traction engines. 



The Woolf Compound. The illustration below 

 shows a sectional view of the "Woolf '-tandem-compound 

 cylinder now used on "Case" compounded engines. Its oper- 

 ation is as follows : The steam from the boiler enters the 

 valve, (which is hollow), through the large opening at the 



FIG. l8. SECTIONAL VIEW OF "WOOLF" COMPOUNDED CYLINDER. 



crank end, passes through the valve and out at the narrow 

 opening near the head end, which, as the valve moves, alter- 



