ECONOMICAL USE OF FUEL IN CREAMERIES. 9 



ordinary material is preferable to a hollow wall of the same total 

 thickness, especially if the air space in the hollow wall is near the 

 furnace side. 



While the solid-wall construction for boiler settings may be better 

 from an insulating standpoint than a wall of the same total thickness 

 containing an air space, in practice it is. advisable to build the walls 

 in two parts in order to assist in preventing the formation of cracks 

 by the expansion and contraction of the brickwork on the furnace 

 side of the wall. The space between the walls, however, should be 

 filled with some solid insulating material, such as mineral wool, 

 crushed brick, ash, or sand, as that kind of filling offers a higher 

 resistance to the flow of heat through the walls than an air space and, 

 furthermore, reduces air leakage into the furnace, which is a very 

 important feature affecting its operation. The air space, however, 

 should be kept so far as practicable from the furnace side. 



The construction of boiler settings differs widely in details, de- 

 pending on the type of boiler used and the local conditions, but the 

 principles governing it remain the same. The brickwork should be 

 substantial, so that it will not crack and crumble, conditions which 

 always produce air leaks and cause extensive repairs. The exterior 

 walls of the setting should be built of hard-burned brick, laid in 

 cement mortar, while the inside lining of the furnace and combustion 

 chamber should be of fire brick laid with fire-clay mortar, care be- 

 ing taken in both cases to use no more mortar than is absolutely 

 necessaiy. The fire brick should be thoroughly bonded into the 

 outer walls, but in such way as to allow replacing' if occasion de- 

 mands. The side walls of the furnace and combustion chamber may 

 be either vertical or tapered. In either case from 2 to- 4 inches 

 should be allowed on the sides of the boiler just below the water 

 line, so that the hot gases can circulate up to the point where the 

 setting meets the boiler, which is usually just below the water line. 

 The upper half of the boiler may be covered with a brick arch or 

 some nonconducting insulating material. When a brick arch is used 

 it is advisable to lay it over strips of wood about three-quarters of 

 an inch thick. When the boiler is fired these wooden strips are 

 burned out, leaving an open space between the boiler shell and the 

 arch through which the hot gases may circulate. Sand should be 

 spread over the arch to close any small crack that may occur and 

 also to act as an insulator. 



METHODS OF SUPPORT. 



Two principal methods of supporting horizontal return-tubular 

 boilers are employed. The one more commonly used, especially with 

 comparatively small return-tubular boilers, is to support the weight 

 on the walls of the setting by means of brackets bolted to the boiler 



82693°— 19 2 



