62 AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 



Table 5. — Inside dimensions of combustion chamber and stack diameters 



Distance 

 from center 

 burner 

 Burning rate of draft tube 

 oil (g.p.h.) to combus- 

 tion cham- 

 ber floor 

 (A) 



Minimum 

 height 



(B) 



(C) Distance 



between 

 Length for nozzle combustion 



angle of- 



chamber 

 and top 

 of arch 



(D) 



(E) 



Width for nozzle 

 angle of — 



80° 



Approxi- Minimum 



mate floor diameter of 



area stack 



Inches inches 



5 9 18 



6 9 18 



7 10 19 



8 11 19 



9 11.5 19 



10 12 19 



12 13 20 



14 14 21 



16 15 22 



18 16 23 



20 17 24 



22 18 25 



24 19 25 



Inches Inches 



Inches Inches 



25 

 27 

 29 

 30 

 32 

 33 

 36 

 39 

 41 

 44 

 47 

 49 

 51 



21 

 23 

 25 

 26 

 28 

 29 

 32 

 35 

 37 

 40 

 42 

 44 

 46 



Square 



inches 



450 



540 



630 



720 



810 



900 



1,080 



1,260 



1,440 



1,620 



1,800 



1,980 



2,160 



Inches 

 10 

 10 

 10 

 12 

 12 

 12 

 12 

 14 

 14 

 16 

 18 

 20 

 20 



corrosive deposits on the underside of the pan; 

 and (2) the ball of fire must be far enough below 

 the pan so that the acute angle of radiation 

 from the apex (ball of fire) to the extreme sides 

 of the pan is kept to a minimum (table 5). If the 

 ball of fire is too close to the pan, there is 

 insufficient space between the pans and the top 

 of the combustion chamber; and the angle of 

 radiation becomes too great. This results in 

 uneven heating across the width of the pan. 

 Overheating occurs directly over the fire. This 

 can be compensated for only by using more 

 than one burner mounted horizontally. 



Construction of Arch and I'onibiistion 

 C.httmher 



Arches may be made of sheet metal or ma- 

 sonry (chart 12). In arches made of either mate- 

 rial, the combustion chamber is free standing 

 within the arch and is constructed of insulating 

 firebrick. In sheet-metal arches the remainder 

 of the arch is lined with hard firebrick. The 

 combustion chamber is separated from the ex- 

 terior wall of the arch by an air space to allow 

 for expansion of the heated bricks. For the 

 same reason, there is an air space between the 

 hard firebrick liner and the exterior walls of the 



arch. The fill between the combustion chamber 

 and the rear of the arch must be of a nonpack- 

 ing material such as cinders. 



Size of Stack 



Since the oil burner is operated under forced 

 draft, the flue stack need not be as high or as 

 wide as when wood is the fuel. The size of the 

 stack is governed by the size of the oil burner 

 (table 5). 



With only one arch, it is recommended that a 

 complete evaporator, flat pan, and flue pan be 

 used. However, it is also recommended that the 

 flue pan be at least two-thirds the total length 

 of the evaporator. The flat pan serves as the 

 semifinishing pan in which the sap is raised to 

 a density of 55° or 60° Brix. The partly concen- 

 trated sap should be transferred from the evap- 

 orator to the finishing pan where the final 

 stage of evaporation is completed. Although sap 

 can be concentrated to sirup in the evaporator, 

 this practice is not advised. 



Installation of Multiple Arches 



To increase the capacity of the evaporator, 

 additional arches and pans can be added. Each 

 additional arch should be equipped with a flue 



