STEAM BOILERS 355 



back end of the grate and to a height equal to the bridge 

 wall. 



Some furnaces and fuels require different depths of 

 fire than others. The proper depth can be determined only 

 by trial. Fine coal and a poor draft require a thinner fire 

 than coarse coal and a strong draft. Engineers differ in 

 regard to the best methods for keeping up a fire. Some 

 suggest that it is best to keep the fresh coal near the 

 door, and when it has become coked push it back to the 

 rear, and again throw fresh coal in the front. By this 

 method there is an intense fire maintained at the back of 

 the furnace, and as the partially burned gases pass back 

 they are completely burned. The advantage of this 

 method lies in the fact that complete combustion is se- 

 cured ; consequently there is less smoke, but there is a 

 corresponding disadvantage in keeping the fire door open 

 so long and allowing the furnace to cool slightly. 



490. Cleaning. Do not clean oftener than necessary. 

 Keep the clinker loosened from the grates between clean- 

 ing times. When cleaning large furnaces, rake all the 

 fire to one side and then clean the grates. Rake a part 

 of the live coals back on this side and put on fresh coal. 

 When this is burning well clean the other side in the 

 same manner. To clean small furnaces, crowd the fire 

 back, clean the grates, then rake the fire forward again. 



491. Banking the fire. Fires are banked to keep the 

 steam from rising when there is a good fire, and also to 

 hold the fire over night. Banking a fire consists in cover- 

 ing the glowing coals with fresh coal or ashes. When 

 banking a fire for the night, crowd the coals to the rear, 

 then fill the front of the furnace with fresh coal, and open 

 the damper over the fire enough to carry off the gases. 

 All drafts should be kept closed. By banking a fire this 

 way it will gradually burn back toward the door, thus 



