Looking for plumbing diagram for flue pipe sap heater

[Polish Wizard]

My search of this site failed to provide any diagrams or photos of a workable pre-heater for a simple gravity system.

So far my plan is to build a barrel stove evaporator.
I'd like to hang a 5-gallon bucket on the wall near the "ceiling" of this proposed tarp-covered shack, and allow gravity to drain the bucket through tubing to the flue stack.

I see bits of info suggesting pros and cons of wrapping copper tube around the flue stack to serve as a pre-heater, especially involving the potential for vapor lock.

Looks like some of the posters suggest wrapping the copper coil with the inlet low in the coil, and rising up the flue before discharging into the collection/cook pan.

There is discussion to install a tee somewhere in this plumbing to serve as a vent for any vapor to rise and expel without disrupting the sap flow.

I assume this coil should be wrapped in some manner to make the best use of heat from the flue.
Any idea how many wraps around a 6" flue would be sufficient and not too much?

Does anyone have any photos or diagrams that show the proper way to do all this, including a vent tube?

[Polish Wizard]

I'm surprised no one has any info to pass along.

[Bucket Head]

I experimented some time ago with a preheater like your describing. It really needs to be "covered" somehow. You need to trap the heat around the coil- you don't get enough contact to the stack for decent heat transfer through conduction. The cover maximizes convection. You may not get enough heat to need a vent. Experimentation is needed. Not a big deal to add one later.

I would not do the outlet higher than the inlet thing. You need to be able to completely drain it of sap, and flush it with water after each use, and that water drain completely. Old sap becomes nasty sap and you don't want that in the copper coil. And you don't need a frozen coil!

Hopefully others will chime in here with what length coil seemed to work well for them.

Good luck this season.

[nekgsa]

I used a pre heater like you're describing. There is a picture of it on the classified right now as the rig is up for sale again. It is the 2x4 with the copper wrapped pre heater. I never had it covered and the sap came out plenty hot into the flu pan. The guy I bought it from said he covered it with foil but that made it to hot and caused vapor locking problems.

[moeh1]

Here is a link with two different styles shown. There is a picture of a wrapped version and a link to Johnny's adjustable version.
http://mapletrader.com/community/showthread.php?19278-How-far-25-of-copper-goes.&highlight=stack+heater

[Polish Wizard]

Thanks for the great responses and links.
I don't know why my search for preheater failed to bring these same or similar links.

I guess "wrapping" with heavy aluminum foil would work, and won't need a fancy fabrication of oversize flue pipe as I first anticipated.
Certainly easy enough to remove aluminum foil if I find the sap gets too hot and boils in the tubing.

Any and all suggestions and concerns (not to mention photos) will be greatly appreciated.

In the next hour I'm leaving Pittsburgh, heading north to the second home. I plan to visit the Amish lumber mill for materials to build a temporary tarp shack before the weather gets rough, and then look into some food grade storage barrels for my anticipated sap collection this spring. And so it begins......

[lpakiz]

I had a preheater like that. One issue was what to do from the time the sap ran out until the batch was finished cooking. You might want to determine how much sap the preheater holds. Then, when you are out of sap, you would dump that much water into the 5 gallon bucket. When THAT water disappears from the bucket, divert the delivery over the side of the pan, into a catch pail, and keep recirculating that water, or new water, till the stack cools. This will prevent any sap from burning in the coils, and keep the coils themselves from getting too hot while you bring the batch to proper density.

[WESTVIRGINIAMAPLER]

Piece of copper tubing ran through your firebox works great as a preheater. Just have it so you can flush it with a little water at the end of the day and it will work great.

[maple flats]

Look up the album and posts by Johnny Cuervo, he made a great pre-heater on the outside of the stack. He describes how he did it and shows pictures. It is a great read. It was adjustable for heat so you could attain the desired temps.