Pre-heater question

[Harken]

I have a 2'x4' flat pan with a pre-heater pan that sits on top. How hot will the sap get in this pan? Would it be worth while adding a coil of tubing around the stack pipe ?

Thanks

Ken

[mapleman3]

Anything helps , you just have to be careful that you don't scorch the sap in the tube, if you cant process the sap fast enough it could burn in tubing and spit and sputter out.

[yooper]

Harken, I made a rig last year exactly like yours from what I can tell in the picture. I left a foot on the back of a fuel oil tank and have a 27" x 48" flat pan that fits it. I kind of wish I would have cut the whole thing in half though for a bigger pan, but...maybe later.

I use a steam pan for a preheater on mine. I have it pushed up against the back of the stove and dip from it into the pan. It doesn't take long at all and you can't put your finger in it and it starts to steam. If I remember right, I was getting around 10 gph last year with this setup.

[Brent]

I had a Leader Half Pint for the last 2 seasons and the preheat pan on it was about 8" wide and sat over the boiling pan. The sap in it never got more than just warn. (Boiling outside on the deck might have had something to do with that.)

Someone on the forum has a similar rig and made a bracket so the preheat pan hung out over the back, where the stack exits the arch. This did two things. It exposed the preheat pan to a lot of heat from the stack and it stopped the condensation from dripping back into the boiling sap.

If I was running the Half Pint this year I'd be making a bracket like this. I think you might need to put a real short extension on the horizontal part of the stack, and you might have to add a little bit of protection between the stack and the preheater so you don't get scorching at the surface of the preheat water. I got that when the preheat water level went down a bit.

Good luck with it

[Jim Powell]

Ken,

I also have a 2’ x4’ flat pan, but mine is propane fired, and not sure how well what I did will translate to wood fired. Mine was custom fabricated by GMB in Wisconsin. It is essentially their “Lil Shaver” design, but larger (2’ X 4’) and fitted with two 210,000 KW burners. The pre heater pan is 2’ x .75’ and holds about 3 gallons of sap I think. I could not find the pre heater on GMB’s website: http://www.gbmllc.com/evaporator.html but did find it on Andersons, which is who I purchased it from. The warming pans are pictured at the bottom of this page. http://andersonsmaplesyrup.com/index.php?main_page=index&cPath=106

What I did was I put a 3/8” Tee on the drain, and from the side arm I ran ½” copper tube over the side of the evaporator pan, and down to a small March Magnetic drive pump I got at a home brew supply house. It comes out of the pump and goes up to the inside of the frame that holds the pan, where it is Tee’d again, and then just runs around the inside of the frame, to a Tee on the other side where it goes down and around the frame, and back up to the other side of the warming pan. The copper tube is nested tightly on the inside of the 2” angle iron frame, and not really in direct flame. I can either just recirculate through one valve, or I can slowly add to the evaporator pan.

At this head it pumps about 6 gallons a minute, so it keeps the sap flowing. Andersons was also concerned about it boiling in the tubes, and I am careful about that. With propane, I have the luxury of just turning off the fire. Anyway, last year I could easily be adding sap that is from 180° to 200° F. I didn’t have any issues, well, at least not related to the pre-heater. I am positive it really allowed me to cook at faster than the 1 gal/ hr / sq. ft. rule of thumb everyone uses.

I have seen some discussion here about a pumpless preheating design that reminded me of a clever wood fired hot tub I had seen once. This must work if they can afford a website like this: http://www.dutchtub.com/ The design is given its own page as well: http://www.dutchtub.com/english00/c_design.php

Some sort of box around the tubing may help with heat transfer. The outside of the tube for heating the hot tub, can be touched even with a fire going on inside the coil. I would also consider a small recirulating pump as well, only because it will minimize the chance of boiling/burning inside the tubing, which is not a pretty though, especially at today’s copper prices.

I love this hobby, you get to tinker with all kinds of stuff, and end up with something sweet!