Copper wrap on stack as preheater

[Dean Poirier]

Just wondering if anyone has tried wrapping copper pipe around there stack to act as a preheater. Would this work or would the sap get TOO hot before entering the back pan.

[michiganfarmer2]

Ive been thinking about the same thing. Ive heard that the sap will boil right in the copper tubing though. Ive thgouht abut maybe keeping the copper a few inches away from the stack somehow

[maplecrest]

i tryed it with 3/8 copper tube put 50 feet around base of stack. and it did not work. would have to be inside stack to be effective

[jtiefert]

We're experimenting with this idea this year. We've only boiled twice, so there are still some bugs to work out.

From the holding tank -> ball valve -> 15' of 3/8" copper wrapped -> needle valve -> batch pan

It needs to be an open system as we've experienced some blow-back into the holding tank.

We added the needle valve with the intent of filling the tubing and trickling the sap into the pan. We still haven't found the sweet spot where we can maintain the level in the pan and not have it boiling in the line.

There are only a few variables to play with - volume in system and flow rate. We're playing with the flow rate.

Sap comes out warmer than it was going in, and it's not killing the boil. We're doing something right.

[Yellzee]

I've been doing this for a few years. Wraps around about 3 times and works great.

I have a valve to adjust the flow and keep it easily at a steady stream without losing my boil.

if I slow it down too much.. or try to shut it off to clean/empty the pan I get issues with it boiling/burning in the line.. so I just fill the tank with water and let it drip slow onto the ground while I do this

[mathprofdk]

This is really interesting. I have this as part of my plan in this post (http://www.mapletrader.com/community/showthread.php?p=145547#post145547). It's starting to sound pretty complicated. Maybe the tin can sitting on the edge of the pan would be better!

@jtiefert: Why the needle valve at the end? Was the sap just flowing too quickly and not warming up? It seems like the length that's coiled would just need to be adjusted according to your stack heat.

@Yellzee: Could you explain the problem with shutting off your valve? Are you talking about whatever sap residue is in there burning? Couldn't you just run some water through to clean it out (let it steam) and then call it good? What's the risk of letting it get hot while empty?

It's also interesting that we have both ends of the spectrum - maplecrest couldn't get it warm even with 50' of copper, and michiganfarmer2 has heard about it getting too hot. It sounds really dependent on your particular system - how hot the stack gets.

~DK

[Kev]

when i did it every time I had it dialed in it worked great. then as the season got later the sap going in was much warmer and I was back to too much heat in the coils.
so it was a never ending proccess that got way to frustrating.

[jtiefert]

We decided to put a needle valve to have 'finer' adjustment of the flow out. Our evaporator would not keep up with uninhibited flow.

Due to vertical space constraints, our 'helix' is not perfect and limits our options for adjusting the number of wraps.

After running out the sap - we've purged / rinsed the lines with water and have let that steam out. We didn't see any problems with doing it this way.

Now I'm going to have to dig out my old heat transfer book... If I still have it.

[Yellzee]

IF I shut off the valve some sap stays in the tubing as my sprial isn't exactly perfect as it boils off it spits out.. so yes, what I do is run some water through it then it's fine.

I find it interesting some folks have trouble with this.. I literally opened a small pack of tubing, wrapped it around the stack and stuck a valve on it so I could adjust the flow. No problems ever getting the mix of flow vs. temp right, I just adjust the valve until it is running right. Maybe I got luck or it's something to do with my set up.

I'll try to remember to take a picture of my set up tonight

[Double-D Farm]

Last year I ran about 6' of 1/2" copper tube inside the stack from the head tank and adjusted the tube discharge valve (into the evaporater pan) to equal my evaporation rate. A problem was that the flow rate had to be increased regularly to make sure steam was not spurting out just after re-firing. I solved that buy increasing flow but then the pan started filling slowly higher than my 2-3" depth. So had to watch it.
Also, if your head tank empties out while still boiling you have to add enough water in head tank to continue tube flow until the boil stops. This water I just diverted into a pail to make hot washing water. Always keep the tube flowing!

[Goin'Broke]

I tried it ,helped a little but heard from someone else who had trouble with it. If it gets too hot it could cause a vapor lock and sap will not flow. Good luck

[barkeatr]

I did that with my half pint it works well. I had it plumbed with a brass screw valve at the end so i control rate. I wrapped the coil just a little loose and that seemed to help it from getting to hot. I would swing it to a pot sometimes when i did not want to add cold sap but at the same time you cant stop flow or it will boil in the pipe. I usually had two copper lines one cold line not going around stovepipe and one that did...

[Maplebrook]

Here is a picture from my old evaporator. 2 runs of 25' each with small valves at the end to control drip into the pan. Would boil sap if flow was slowed too much. Worked great!

[woodsmith]

I used this method to great effect; on my old barrel stove I used 1/4" copper tubing around the 6" flue pipe, wrapped around 3 or 4 times and then wrapped the coil with fiberglass insulation held in place with steel wire. You have to boil at a fast enough rate to keep the sap moving through the coil but it can be done. Sap came out of the tubing too hot to touch. You just have to experiment with number of times going around the flue and how fast you feed the pan.

[wnybassman]

What happens when you get to the end of the sap supply? I don't imagine letting the coil go dry is a good idea? I've often thought this method of preheating, but that question always stopped me.

[sniperdodo]

once you have run out of sap, just open the valve at both ends to allow air movement and the copper will be fine

[wnybassman]

once you have run out of sap, just open the valve at both ends to allow air movement and the copper will be fine

I guess I wasn't really worried about the copper itself, but more of the sap residue on the inside of the pipe burning to a crisp. Maybe this isn't a concern.

[Maplebrook]

The sap residue will burn to a crisp. The next boil, get the coil hot again and then let the cold sap run through. It will "hiss and spit like a pissed viper" (credit to who for this famous qoute???) and then clear out and work fine. Catch the spittins' in a pot so it doesn't land in the pan. You're back in business!

[Buckshot]

Look at my pics in my avatar that's how i do mine. 100 feet of copper.
I have use it twice, works good. Any rise of temp of sap is good
because it won't steal energy from your evap.

[ca2devri]

Guys,

This discussion made me decide to try this. I have some 3/8" soft copper lying around. But: how do you wrap the copper tightly around the stack? Any hints for how to do this easily without crimping the copper?

Chris

[Buckshot]

very slowly and if you kink it can be squeezed out some what with channel locks

[Maplebrook]

Trial and error...Here's what I finally did.
The stack for the evaporator was 8". I took an 7" diameter piece of stove pipe and wrapped the copper around the smaller pipe. As it was hard to bend the tubing tight to the pipe, by the time this was done it just had to be sprung slightly to slip it over the 8" pipe.
The preheater was 2 - 25' runs of tubing. I straightened them out and laid them on the floor, used small band clamps to hold them together, and rolled the pipe along the floor and coiled the tubing around.

[cjmiller272]

I wouldnt see why you cant put a valve at head tank, then a tee with one end going toward stack the other end as an open breather extending above the head tank. Then open valve accordingly, err on shorter length of tube to prevent scorching before it exits into the pan. With no bottom valve, line is never storing sap on stack and with valve being before tee any expansion/steam just vents out the top.

[lfdiaff]

My plans were 3/8s as well. I plan on using a 8" stack so that bend shouldnt be to bad. If it starts to kink fill it with water and freeze it.

[Starting Small]

I purchased a 2 X 3 mason with a preheater. Is there any benefit of doing this and having the tubing empty into the preheater?