66 



SCIENCE OF SUCCESSFUL THRESHING. 



in the chambered steam-chest cover, so that, when the valve 

 in the small steam pipe connecting this chamber with the 

 main steam-pipe is open, the live steam pressure against 

 the plugs holds the valve against its seat. 



To Take Apart the Compound Cylinder. To take out the 

 pistons for renewing the piston-rings or for other pur- 

 poses, first unbolt and remove the high-pressure cylinder. 

 Then loosen the jam-nut and unscrew the rod from the 

 cross-head by turning the pistons. The rod with the two 

 pistons and the center-head may now be pulled ut. In 

 replacing the cylinder, loosen the three, (or four), set-screws, 

 which hold the center-head in position, and after the high- 

 pressure cylinder is bolted in place, tighten them up in order 

 to hold the center-head in position and pr.event leakage. If 

 the asbestos gasket has been injured it will be necessary to 

 put in a new one. 



Center-Head Packing. Leakage around the rod, between 

 the two cylinders, is prevented by metallic packing, which 

 will, with sufficient lubrication, remain tight during the life 



of the engine. The 

 accompanying cuts 

 show a side and a 

 sectional view of 

 the metallic pis- 

 ton-rod packing 

 which is located 

 FIG. 21. THE CENTER-HEAD PACKING, in the center-head 



