ECONOMICAL USE OF FUEL IN CEEAMEBIES. 25 



develop after the setting has been in operation it can be stopped 

 easily with asbestos rope and fire-clay mortar, as previously described. 

 When the front is broken it is difficult to repair and when badly 

 broken should be replaced with a new one. Care should be taken to 

 construct the masonry so as not to allow the intense heat of the 

 furnace to be conducted to the cast-iron front. 



Fire and ash-pit doors are often badly fitted, warped, or broken, 

 allowing too much cold air to enter the furnace. While it is neces- 

 sary for air to be admitted at those points, the doors should fit 

 tightly, and the volume of air admitted should be under the control 

 of the fireman. 



Flue doors seldom close tight, or if they are capable of being 

 closed tight the fireman often neglects to do so. As the hot gases 

 leaving the tubes impinge directly upon these doors, they are often 

 warped and broken from excessive heat, thus allowing the entrance 

 of air at that point. 



With the horizontal return-tubular boiler it is very common to 

 find that the weight of the boiler has caused the settling of the brick 

 arch, thus leaving an opening between the end of the boiler and the 

 top of the brickwork, through which the hot gases from the furnace 

 pass directly to the stack instead of taking the path from the, fur- 

 nace through the combustion, chamber and the boiler tubes, resulting 

 in a high stack temperature. This short circuiting of the flue gases 

 causes a large loss of heat in the stack with a corresponding decrease 

 in furnace efficiency. 



Almost invariably the opening through the wall of the setting 

 through which the- blow-off pipe passes is made larger than necessary, 

 thus allowing cold air to enter the combustion chamber and lower the 

 temperature of the gases and consequently reducing the effective 

 draft. The door and frame of the clean-out door arc more often 

 than not found to be cracked or badly fitted. The back arch is forced 

 back, due to the expansion of the boiler, until there is a permanent 

 opening between the end of the boiler and the arch, through which 

 large quantities of air pass directly to the boiler tubes. The back 

 wall of the setting is very often cracked from the- expansion of the 

 boiler at the points indicated in figure 5. 



While the foregoing are the places in the setting of a horizontal 

 return-tubular boiler where air leaks occur most frequently, there 

 are other points through which outside air finds its way into the 

 furnace and combustion chamber. The side walls of the setting 

 frequently develop cracks, and the entire brickwork is more or less 

 porous and allows air tb " soak " through even though there are no 

 visible openings. It is obvious that in order to obtain reasonable 

 economy in a boiler plant the air leaks must be stopped. 



