18 BULLETIN 747, U. S. DEPARTMENT OF AGBICULTUBE. 



FIRE DOORS. 



The fire doors should be of substantial construction and should fit 

 tight in order to prevent cold air from entering the furnace over the 

 top of the fuel bed. An adjustable opening having a clear area of 

 about 4 square inches per square foot of grate area should be pro- 

 vided in the door through which air may be supplied above the fuel 

 bed. The admission of air through these openings also tends to 

 keep the door from overheating and warping. 



UPTAKES. 



The smoke connections between the boiler and breeching are called 

 uptakes. These connections should be as straight as possible, with 

 ample cross-section area in order not to hinder the draft. The cross- 

 section area should be from 20 to 25 per cent greater than the com- 

 bined tube area, or approximately 25 per cent of the grate area. If 

 it is impossible to run the uptake connections straight to the breech- 

 ing, large, easy bends should be employed. Abrupt bends materially 

 reduce the draft. Uptakes are often fitted loosely to the smoke out- 

 let of boiler and to breeching, thus allowing cold air to enter and 

 cut down the draft. Care should be taken to see th-it these connec- 

 tions as well as all others are made tight. 



BREECHINGS. 



Breechings are the connections behveen the uptake and the chim- 

 ney. They should be run as straight as possible and bends, if un- 

 avoidable, should -be large and sweeping. Breechings may be hori- 

 zontal, but it is much better to have them rise from the uptake to 

 the chimney. Under no consideration, however, should they drop 

 below the horizontal. They should have a cross-sectional area of at 

 least 25 per cent greater than the combined tube area, or one-fourth 

 of the grate area. Round or square breechings are preferable to 

 broad, flat ones, as the resistance offered to the flow of gases is not so 

 great in the former as in the latter. In no case should a breeching 

 be used in which one dimension is twice that of the other. Both 

 uptakes and breeching should be tight and carefully covered with a 

 good quality of heat-insulating material. 



HAND FIRING OF BOILER FURNACES. 



Boilers employed in "the dairy industry arc generally small, al- 

 though ranging from the smallest size which is used on the dairy 

 farm to several hundred horsepower in the largest milk plants. The 

 great majority, however, range from 10 to 50 horsepower. The con- 

 ditions and methods of operation used in these small plants are 

 entirely different from those plants emploj'ed solely for the genera- 



