IIO SCIENCE OF SUCCESSFUL THRESHING 



The Blower. The blower consists simply of a pipe 

 leading from the boiler to a nozzle in the smoke-stack. In 

 the pipe is a valve for shutting off the steam. On traction 

 engines usually a rod is fitted to this valve, allowing it to 

 be operated from the platform. The blower is intended 

 for use only in raising steam, when the engine is not 

 running. When the engine is running, its exhaust is dis- 

 charged into the smoke-stack, creating what is known as 

 "forced" draft, as distinguished from "natural" draft, 

 which is due only to the height of the chimney. When an 

 engine has been running and is temporarily shut down 

 the blower should not be used unless the entire grate sur- 

 face is covered with burning fuel. If the blower be used 

 soon after shutting down and the grates are not entirely 

 covered with burning fuel, cold air will pass through the 

 dead places in the grates direct to the tubes, cooling them 

 suddenly and rendering them liable to leak. 



The Fusible Plug, sometimes called the "safety-plug" 

 or "soft-plug," is intended to melt and prevent the crown- 

 sheet from injury by low water. However, 

 it cannot be entirely relied on, for the upper 

 end is apt to get coated with lime or scale 

 and render it useless. It should be taken out 

 two or three times during the season and 

 scraped clean, and a new plug should be put 

 FUSIBLE PLUG in or the old one refilled at the beginning of 

 3N> each threshing season. In screwing the plug 



