MAPLE SIRUP PRODUCERS MANUAL 



41 



PN-mi 

 Figure 75.— The hot steam causes a natural draft and 

 does not require air intake ports. 



light wooden frame of gable design made from 

 1- X 4-inch pitch-free lumber (spruce or bass- 

 wood). The aluminum sheets are cut to size and 

 are attached by aluminum nails to the inside of 

 the wooden frame, completely covering the 

 wood so that it is not exposed to the steam. 

 Galvanized iron should not be used, since the 

 acidic gases in the steam will quickly corrode 

 and dissolve the zinc coating. 



A satisfactory pitch of the gabled cover is 6 

 inches to the foot, or 30°. The walls of the cover 

 should be 6 to 8 inches high to provide adequate 

 headspace for the free boiling sap. A trap door 

 should be placed over the flue (back) pan to 

 permit inspection and skimming. However, the 

 tight cover has practically eliminated the need 

 for skimming. This is no doubt due to the 

 absence of air ft-om the steam-filled area above 

 the boiling sap. 



The pipes for the stack or steam vent should 

 be made of the same lightweight metal, and 

 they can be fabricated in any sheet-metal shop. 

 The stack should be placed over the flue or sap 

 pan, because that is where inost of the steam is 

 generated. The stack should be fastened at its 

 base to the evaporator cover. It should be long 



enough to extend up to and through a hole in 

 the roof of the building to 1 foot above the ridge 

 of the roof. 



The opening in the roof should be 1 inch 

 larger in diameter than the stack, so that the 

 stack can be moved freely. The diameter of the 

 stack is not critical; however, it must be large 

 enough for the steam to escape readily. Stacks 

 of different diameters are required for different 

 size covers, as follows: 



5 14 I ig 



5 20 I 



' For covers over flue pans use next larger diameter; 

 for covers over sirup pans use next smaller diameter. 



For evaporators with two or three sections, it 

 is easier to construct separate covers with indi- 

 vidual steam stacks for each section. 



To remove the cover, hoist it and the at- 

 tached steam stack vertically — push the stack 

 up through the roof opening — by means of a 

 I'ope attached to eye bolts at each end of the 

 ridge pole of the cover. Pass the rope through 

 pulleys located overhead and then down to a 

 windlass mounted at a convenient height on 

 the sidewall of the evaporator house. 



I^ocation of" K\a|><n-ator 



The evaporator should be located directly 

 under the ridge of the roof and centered under 

 the hood (if an open hood is used). The founda" 

 tion for the evaporator arch should be made of 



