86 



SCIENCE OF SUCCESSFUL THRESHING 



is on top, and pressing it against its seat. When the 



engine is running with 

 a light load, the pressure 

 is sometimes insufficient 

 to hold the valve against 

 its seat, in which case a 

 loud clattering noise is 

 made by the valve as it 

 rises from and returns 

 to its seat. To prevent 



FIG. 26. PIPE TO STEAM PLUGS. this, two steam plugs 

 are placed 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 Compounded Cylinder. To take 

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

 purposes, first unbolt and remove the high-pressure cyl- 

 inder. 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 

 out. 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 

 prevent leakage. If the asbestos gasket has been injured 

 it will be necessary to put in a new one. 



