3/8 preheater

[garyp]

Is making a preheater with 3/8 lines going into 1/2 headers to small to use, I have a 30'' x 5' flat pan and a 25' of 3/8 coil copper tubing to use.
Not to keen on the rap around the stack idea but like the idea of using the steam off the pan

[Paul VT]

It should work. With a flat pan your evaporation rate will be lower than a rig with a flue pan so should work fine. You should make some kind of a drip tray for it so all the condensation isn't going back into your pan.
Anything to warm your sap before entering your pan will help. I think your efforts building a preheater would better then wrapping coil around your stack.

[acerrubrum]

What is the main difference between the wrap around the stack and a manifold type preheater? Is the manifold type just better, more efficient? I'm thinking of doing either one for my 2 x 4 flat pan and I like the idea the coil wrap around the stack, and using some of the heat escaping out the stack, and not having to deal with the drips and vapor locks etc that seems to come with the manifold style.
The thing I can't figure out with the coil wrapped around the stack is how to match the coil diameter size, and number of wraps so I get enough sap to keep up with the evaporator and to have it hot enough. It seems like it could easily be not enough preheated sap, or too much and then it boils in the coil.

[vtwoody]

Main difference is manifold heated by steam (temp @212F), as opposed to coil around stack heated by 800F, 900F+?

I have a 2X4 dropflue and tried the coil around stack last year. Biggest challenge was keeping up with demands of pan. The 1/4 " or 3/8" line I used was not flowing fast enough to keep up with evaporation rate, especially once stack got heated up. Sap started getting warm and all of a sudden outlet end started spitting and steaming and flow stopped. Sap was being evaporated in coil (scorched plus no flow into pan) before it could get to outlet. Yes, I had an air release tube after sap tank and before coil went around stack to release pressure - didn't stop sap from being vaporized.

It's very likely I could upsize coil and have enough flow to avoid vaporization and keep up with demands of pan evaporation. the problem is the extreme temp of stack, as well as the variability of that temp. In the middle of boiling, you don't need one more thing to keep you eye on that could spell disaster.....

A little more work to do the manifold but I'm giving it a shot this year since I have a hood already. For a 2x4, or 2X6, it's not a lot of pipe, you avoid the concern of scorching and, with a hood that has a drip channel with outlet (necessary, apparently, top get much efficiency from a manifold pre-heater) you have a supply of clean, hot water.

Anything is better than nothing but scorched sap =nothing, lol....lesson learned through experience...priceless

[garyp]

Well found out that the 3/8 pipe is a little to small for my evaporator, at a little trickle temp was around 120 but my evaporation rate was a little greater and with more flow was about 60, so next year I will go with 3/4 pipe
Oh by the way I did make a hood for my preheater and works pretty good keeping drips away and steam in

[CTsugarMan]

So is a manifold simply a hood with some pipelines running through it that the SAP travels through on its way too the pan for boiling, but it arrives at the pan close to a boiling temp?

If so anyone have plans or pictures they can share
Thanks

[acerrubrum]

Vtwoody, thanks for the reply. It seems like you experienced the things I was concerned would happen. It makes a lot of sense about the temp variance in the stack, whereas the steam temp around a manifold would stay pretty even-I didn't think about that. I was leaning towards doing the coil wrap but now I think I'll think about it some more. I'd rather do some more thinking than deal with scorched sap. I'm also not crazy about testing the coil wrap during a full boil anyway.

[Scribner's Mountain Maple]

Good thread, I am facing a similar decision today. I have a question about what will give the most heat transfer? I currently have no hood, and no preheat. I do have a 3/4 " line coming from my tank that goes through a filter and then into my float set up. My arch is 4*12.

I have a 30-40' piece of 3/4 soft copper. Should I wrap around stack, or build some sort of Manifold? I have very little sheet SS that I could suspend above the pipe, and certainly I can put some sort of tray under it.

If I go with the stack, I don't think I would be able to wrap it more than 2-3 times. And if I go with stack should soft copper touch the stack or should I suspend away .5 ". I'm thinking that with the short piece of copper that vapor lock won't occur.??

I am not looking to spend money on more SS sheet material. However I do want to get my sap as hot as possible before it hits the pans.

Thanks