Preheater Hood Material

[ren46]

I'm in the planning stages of building a hood for my preheater assembly and was wondering if aluminum sheeting would be ok to use as a cheaper alternative to stainless steel. I plan on using rivets for assembling the sections together and already have the rivet tool and plenty of aluminum rivets on hand.

Ren

[whity]

Ours is all aluminum sheeting. With stainless rivets. hardest part was keeping it from oxidizing. Last fall I polished the whole thing and gave it a coat of high temp clear paint. Looks like new. Even after boiling a season.

[maple flats]

Aluminum is fine. My first 3 evaporators had aluminum hoods I made, the current one was going to except at the factory when I picked the new pans up they asked if I was interested in a SS hood. I said I was going to make an aluminum one but it turned out they had a SS demo, 1 yr old that had 2 very small dings in them and they offered them to me for $800, the original quote for the same thing when I was ordering the pans was a little over $1900. I thus bought the SS hoods, the price included 2 steam stacks @ 15" (the flue pan stack included an adjustable lockable damper) that went up 4'. I made the rest out of aluminum, 13" which suspends in the cupola and extends about 6-8" into the 15" SS stacks. I made a double layer pre-heater a couple of years later out of copper, it works quite well. I have a thermometer in the line going to the float box, it often reads about 170, higher would be better, but 170 is about 135 higher than what the cold sap was at.
When you make your hood, be sure to add a damper in the stack, then in operation slowly close it until some steam just starts to escape out cracks between the pan and the hood. From there, open it very slightly and lock it in position. The better the steam is trapped around the pre-heater the higher the sap temperature will get.
If memory serves me, I increased my boil rate by 16% adding the pre-heater.

[ren46]

Steve and Dave,
Thanks for the info. I'll use aluminum and fashion some sort of damper to control the steam. If it warms up the cold sap better than my old pan that sat on top I'll be happy!

Ren

[maple flats]

Just be sure to use as much copper (or SS) tubing as you can fit in the hood, the more the better. It will heat well. In my 3x5 flue hood I have a 1 x 1/2 manifold with 6 take offs in the 1/2". it starts low at one end and at a slight angle climbs to the other end where it is soldered to another manifold the same. The cold enters on one side and the warm exits the other side after going thru the 1/2" tubing. Then I have an elbow and s street ell and a vent TEE to rise to a second level where it enters a 3rd manifold. Then the tubing rises until it gets to the final manifold and the exit. Each of the 2 tiers rise 2.5" from one end to the other. I put a vent at each corner just in case but I've never had to vent even one in the years I've used it. The entrance and exit 1" tubes pass thru the hood. Between the head tank and the inlet to the hood, I have a valve to stop the flow, a tee and a drain valve which empties the feed line directly into the float box. On the exit it has a tee wihich turns the flow downward and mounted in that TEE is a thermometer to read the sap temp. I only used 1/2" copper and each length is 52", but with 12 pieces that length in the steam, plus 4 manifolds 15" long 1" x 1/2" (x6) I take the sap from about 35F up to 170F (however when I have just reversed the flow in the syrup pan, the first draw takes longer and the sap gets up to 180-185) except towards the end of a draw, when the temp falls to 115-120F. I think if I'd used 1 x 3/4 (x6) manifolds for more surface area and slower flow thru each tube I might have gotten another 20-30F. I might make that change at some point but for now I'll use what I have. For manifolds on earlier pre-heaters I just used street tees but on this one I bought like these for a more compact unit .supplyhouse.com/Sioux-Chief-678-20644-1-Copper-Manifold-w-1-2-Sweat-Loops-6-Outlets?gclid=EAIaIQobChMIvv_Djfnw1gIVAoxpCh1jrgot EAYYAyABEgLXY_D_BwE
Those are also available in 1.25 x 3/4 with 6 or 8 leads off, that I now think would have given better results.
More money spent now can yield bigger results for a long time.