60 



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



PN-4'H.l 



Figure S8. — A correctly positioned, single, high-pressure, 

 domestic-type burner will give the required heat for the 

 evaporation of the sap. 



If one burner is used, it should be mounted 

 far enough below the bottom of the pan so that 

 the radiant heat will be effective across the full 

 width of the pan. If construction of the arch 

 does not permit mounting the burner this far 

 below the pan (see table 5), then two or more 

 smaller burners mounted horizontally should 

 be used to insure heating the full width of the 

 pan (fig. 89). If the slope of the arch is such that 

 the undersurface of the flue pan cannot be 

 illuminated by the ball of fire (see chart 12), 

 boiling may not occur in the area not illumi- 

 nated. This is especially true of wood fuel 

 arches that have been converted for oil burn- 

 ers. To compensate for this, a supplementaiy 

 firebox can be constructed under the flue pan. 

 and another burner mounted; however, this is 

 not always satisfactoiy. 



\ftzzh' Tip 



For evaporators in which the length is ap- 

 proximately twice the width, the nozzle tip 

 should be at an 80° angle. For evaporators in 

 which the length is greater than twice the 

 width, the nozzle should be at a 60° angle. 

 Irrespective of the type of nozzle tip or the 

 angle, the burner must be adjusted so that the 



PN-47S5 



Figure 89. — When one large burner cannot be mounted 

 sufficiently far below the pan, two or more .smaller 

 burners can be mounted horizontally to give the re- 

 quired amount of heat without danger of producing hot 

 spots. 



correct amount of air is fed along with the 

 atomized oil to insure complete combustion. 

 This can be checked with a flue gas analyzer. 



Arvh 



,1 ( 



ihiisti 



( h 



The arch for oil fuel also serves as a support 

 for the evaporator pans and contains the com- 

 bustion chamber and the flue for the hot gases. 

 The arch should be located in the evaporator 

 house to provide an adequate working space 

 with room for installing supplemental arches as 

 the operation is expanded. The arch need not 

 be in the center of the evaporator house but 

 may be at one side. The concrete footings for 

 the arch should be on gravel and should extend 

 below the frostline. An all-masonry arch, with 

 external walls built of cinder block or brick, 

 may be built on the site, or the arch may be 

 prefabricated with exterior walls of sheet metal 

 on a cast iron and steel frame. In either case, it 

 must conform to certain minimum dimensions. 

 The interior construction is similar for both. 



Dinu-nsioiia <>/ trr/i.— The size (length and 

 width) of the arch is determined by the size of 

 the evaporator. It must be wide enough to 

 support the pans and long enough not only to 

 support the pans but also to hold the base of 

 the flue-gas stack. Chart 12 shows a masonry 

 arch for a 5- by 12- foot evaporator (9- foot flue 

 pan and 3- foot flat pan). The outside walls are 



