raised or drop in flue

[damaille]

I am learning about the evaporators and how they work. What is the difference between a raised flue and a drop in flue? which is more efficient?

[waysidemaple]

A drop flue evaporator has one float box that controls the level of sap in both the flue pan and syrup pan. The flues on the flue pan actually sit down inside the arch. On a raised flue the flue pan and the syrup pan are controlled by two different float boxes, and the flues dont sit down in the arch. I have a drop flue 2 x 8, but if I had it to do over I would go with a raised because then I could run the flue pan much lower than the syrup pan and increase my evaporation rate. I think thats it in a nut shell. Im sure others will point out differences I missed.

Scott

[damaille]

Thanks Scott.... so a raised flue would increase evaporation rate and have more control?

[markcasper]

I have always believed you get a bit more evaporation from a drop, but a little more trickier to run.

[Ausable]

I am learning about the evaporators and how they work. What is the difference between a raised flue and a drop in flue? which is more efficient?

Will tell You the little I know -- Normally the flues are located on the Sap pans. The idea of flues is to expose as much surface area as possible to the heat and get the sap boiling quicker and more efficiently. The sizes and styles vary with the manufacturer and with the homemade rigs the sky is the limit. You understand the idea of the flow thru - the sap starts its adventure to syrupland back in one of the sap pans and winds its way thru the sap pans to the syrup pans and finally to the drawoff point in the last syrup pan.
OK - If You are standing in a Sugar House looking at the Arch and Evaporator (I'm talking about a traditional wood fired Rig where everything is not all covered up and you really can't see it) and You notice that the Sap Pans in back sit higher than the syrup pans in front - You are looking at a raised flue evaporator (The flues will be out of sight under the sap pans and the bottom of the flues will be about even with the bottom of the syrup pans). OK - We drive up the road and go into another Sugar House and at this place - all the pans on the evaporator look even and it is a factory rig - chances are this is a drop flue evaporator and the flues on this one hang lower and hang below the bottom level of the front syrup pans which are usually flat pans. OK - Now to answer Your question - Which is best - Raised or Drop Flue? My Friend - I have NO opinion - cause to answer that one would stir up a half dozen Hornets Nests and I just ain't brave or foolish enough to even try. --- Mike

[Jeff E]

I am not sure what would make you run deeper in the syrup pan with a drop flue. I usually run at 1.25 to 1.5" depth in my drop flue evaporator.

I like the idea of one less float box to keep track of, (sticking closed, or open) and the quicker flow response of an open channel between the sap and syrup pans. Quicker flow means less chance of scortching when you have big draw off of syrup, which seems to happen more often than it should in my sugar house. (after switching sides, after missing a firing by 2 minutes for whatever reason, and there a way to many reasons/excuses:lol:)

[damaille]

Thanks guys, I am looking into purchasing my first evaporator and leaning toward the Patrick Phaneuf 2x6. with not having any experience with these want to know what is the best set up to go with to last years to come without wishing I went with something else. I see here more and more get hooked and all of a sudden very quickly have to upsize to grow. I did 25 taps this year and will most definately have more than 200 for next season.

If anyone has any recommendations, I am all ears.


Thanks

[Gary R]

200+ buckets, or vacuum? If it's vacuum, you'll be boiling 10+ hours a day when the sap runs. estimate how much sap you'll get and how much time you have. Guess at about 10 gal. average per tap on woods trees buckets and maybe 25 gal. per tap average on vacuum on the same trees.

[Sugarmaker]

Drop flue vs Raised flue? I have only boiled on flat pans and drop flue pans. But there are a lot of raised flue pans doing a very nice job making a lot of syrup!
Try to get to a sugar house that has each and take a good look. They both need sap over the flues to operate very long.
Chris

[Thad Blaisdell]

On a 2x6 the difference is so small that it would make no difference, find a good used one and buy the one you can get a deal on. You would have to have a bigger rig to notice any significant difference.

[red maples]

I have a phaneuf drop flue 2x6 on 280 younger red maples on vacuum and the best week I had I got 250-310 gallons of sap a day for I think 7 days staright which = 7-10 hours of boiling a day just to keep up. on avarage I boil 35-38 GPH and if I really push it I have reached over 40 earlier in the season before the carbon builds up on the bottom by the end of the season in cuts down a little. thats with bone dry Pine. I was firing every 3-4 minutes but that was killing me so I just fill it heavy and let it go longer now. (much more enjoyable)

[red maples]

Sorry I give up I have tried several times and even tried private message keep getting a server error!!!! ????

Damille if you PM me your email I will give you some more info on my PHaneuf 2x6.

[DrTimPerkins]

Thanks Scott.... so a raised flue would increase evaporation rate and have more control?

The difference in evaporation rate in that case is due to running it shallower. The increase would be very small (especially in an evaporator that size), since it is only increasing evaporation a little bit in the syrup pan. Most of the evaporation takes plance in the flue pan.

For completeness sake in this discussion, there is also another style that is a hybrid between the drop and raised flue. It has both drop and raised flues. Leader Evaporator calls it the "Max" flue pan. Basic idea is to maximize surface area for heat exchange. Not sure whether other manufacturer's have anything similar, or what they're called if they do.