86 



SCIENCE OF SUCCESSFUL THRESHING. 



FIG. 28. SECTION 

 OF SIPHON. 



entering steam, to the bottom, where 

 it condenses in the chamber, and thus 

 effectually prevents any live steam 

 from reaching the spring of the gage. 

 The cap over the pipe falls when 

 the pressure is removed, making a 

 siphon, which is self-emptying, and thus 

 all danger of bursting by frost is over- 

 come. The cock should always be left 

 open. 



The Pop Safety Valve. The safety 

 valve opens when the pressure reaches 

 a certain point, allowing the excess 

 steam to escape .and closes 

 when the pressure has been 

 reduced a few pounds. The 

 valves are usually set at the 

 factory to blow off at one 

 hundred and thirty pounds. 

 If a change of pressure be de- 

 sired, unscrew the jam nut at 

 the top and apply the key, 

 provided for this purpose, to 

 the pressure screw. For more 

 pressure, screw down; for 

 less, unscrew. After having 



obtained the desired pressure, 

 FIG. 29. 



SECTIONAL VIEW OF POP VALVE, screw the .jam nut down tight 



