24 



BULLETIN 747, U. S. DEPARTMENT OF AGRICULTURE. 



on account of lack of air to burn them will cause smoke. The smoke 

 thus formed will issue from all cracks and openings in the setting 

 and bo'iler doors, which should be marked for repairs. 



Another method is to go over with a lighted candle the outside 

 surface of the setting around the boiler front, flue doors, clean-out 

 doors, and other points where air leaks are liable to occur. Where 

 leaks occur the flame of the candle will be drawn in, due to the 

 inrush of air. In order to make the flame more sensitive, the candle 

 may be placed in a box having both ends open, one end of the box 

 being moved over the surface of the setting. 



Ifter finding the leaks the openings should be packed with 

 asbestos rope saturated with fire-clay mortar. The rope should be 

 forced well into the crack and the latter pointed up with the mortar. 

 After all the leaks have been stopped several coats of a good quality 

 of heat-proof paint should be applied to the entire setting. The paint 

 effectually seals all small cracks that may have escaped detection 



and also prevents 

 the absorption of air 

 through the walls, 

 clue to the porosity 

 of the bricks. 



A large part of the 

 excess air which en- 

 ters through cracks 

 in the walls of the set- 

 ting does little or no 

 good in completing 

 the combustion of 

 the fuel. Air enter- 

 ing at the rear of 

 the setting or into 

 the uptake, breeching, or chimney not only has no effect on the 

 combustion of the fuel but cuts down the draft at those points and 

 makes it difficult to get the necessary volume of air through and 

 over the fuel bed. It is very important, therefore, that all parts of 

 the setting, uptakes, breeching, and chimney be made tight. 



Figure 6 shows the points where air leaks are most commonly 

 found in a horizontal return-tubular boiler and its setting. 



The cast-iron boiler front is a frequent source of air leaks, as it 

 is frequently warped or broken, clue to the heat from the furnace, 

 and often it is not placed in position properly, cracks through which 

 the air passes being left between the front and the brickwork. 

 When installed the space between the front and the brickwork 

 should be carefully filled with cement mortar. Should a crack 



p IG . (;. — Common sources of air leaks in horizontal 

 return-tubular boiler settings. 



