Help balancing between pans - 2x8 raised flue

[Willen]

I’ve been a flat pan guy, until this year. I’ve been running a new to me Waterloo-Small 2x8, raised flue 2x6 back pan and flat 2x2 finishing pan on front. No blower, approx 15’ of stack, 2 float boxes. I run about an inch in the front pan, and an inch over the flues, and often struggle to maintain a hard boil in the rear pan without boiling over the front. I’ve found I need to watch the wind direction, and really chuck the wood in to the back of the fire box, even up the ramp so it’s under the front of the raised flue pan. So maybe I need some more stack for a better draw?

Also noticed that I need to keep the volume of syrup in the front pan down, as the float box can leak a bit, then I end up with more liquid that expands higher.

Draft door is between half open and fully closed. Wood is dry and split small. Feeding RO concentrate, around 6 Brix.

Experience and suggestions appreciated!

[TapTapTap]

Maybe you need a blower on the arch. We find that our blowers not only fuel the fire but also move the heat to the flue pan more efficiently. And we can adjust the blowers to concentrate the heat.

Ken

[Brian]

How tall is the stack it should be at least twice as tall as the evaporator is long. A 2x8 should have a stack at least 16 tall.

[BAP]

Also to add to Brian’s comment about the stack, it should also be taller than anything else on your roof. You don’t have a damper in your stack do you? If so, don’t use it, stack should be wide open. As Ken pointed out, sounds like you need more air flow to the fire to keep pushing the heat back in the evaporator.

[johnallin]

I’ve been a flat pan guy, until this year. I’ve been running a new to me Waterloo-Small 2x8, raised flue 2x6 back pan and flat 2x2 finishing pan on front. No blower, approx 15’ of stack, 2 float boxes. I run about an inch in the front pan, and an inch over the flues, and often struggle to maintain a hard boil in the rear pan without boiling over the front. I’ve found I need to watch the wind direction, and really chuck the wood in to the back of the fire box, even up the ramp so it’s under the front of the raised flue pan. So maybe I need some more stack for a better draw?

Also noticed that I need to keep the volume of syrup in the front pan down, as the float box can leak a bit, then I end up with more liquid that expands higher.

Draft door is between half open and fully closed. Wood is dry and split small. Feeding RO concentrate, around 6 Brix.

Experience and suggestions appreciated!

Have you cleaned the bottom of the raised flue pan? I have 2x6 Leader Patriot with raised flues..they're hard to clean unless the pan is pulled off the arch.
Drop flues are much easier to clean with a brush while in place. Maybe they're all sooted up?

[ecp]

Another possible thing could be the insulation below the flue pan is to low and not forcing the fire up into the flues.

[Brian]

I guess we are all saying is you need more draft. This will move the heat back under the flu pan and all are valid points. All of these things matter. Good luck

[johnallin]

I guess we are all saying is you need more draft. This will move the heat back under the flu pan and all are valid points. All of these things matter. Good luck

Looks like Willem has 15' of stack.
Another 3' section may make all the difference...but I'd still make sure the flues are fairly clean.
That heat under the front pan has no where else to go but up and out.
Sure sounds like it's not being transferred to the flue pan.
Just my 2 cents.

[nhdog]

i'm not an expert, but if you have a good boil going on the front pan you must have good heat in the fire box and in order to get the heat going anyplace it must go out past the sap pans flues. what does your stack temp read ? if it is good than your fire side on the flues are too dirty to transfer the heat thru to the sap or the heat is not being forced up thru the flues. i don't know about your waterloo but on my lapierre raised flue small evap, the blanket insulation over the ramp must be touching the bottom of the flues this ensures the heat goes where it is supposed to go. there has been lots of suggestion so this is just more food for thought.

[johnallin]

i'm not an expert, but if you have a good boil going on the front pan you must have good heat in the fire box and in order to get the heat going anyplace it must go out past the sap pans flues. what does your stack temp read ? if it is good than your fire side on the flues are too dirty to transfer the heat thru to the sap or the heat is not being forced up thru the flues. i don't know about your waterloo but on my lapierre raised flue small evap, the blanket insulation over the ramp must be touching the bottom of the flues this ensures the heat goes where it is supposed to go. there has been lots of suggestion so this is just more food for thought.

You’re more of an expert than you think.
Checking stack temp is a great indicator and agree 100% with the flues being dirty.

[maple flats]

A couple of things I notice. On my 3x8 I never had such an issue, but I did find it important to have the wood split wrist size, fill every 7 minutes by a timer, before I added AOF, (high pressure air over fire). To do that I made a manifold that I mounted all aroundthe top on the inside of the firebox. The manifold was only 2x2" tubing even though instructions from Proctor Maple Research stated 3". In the manifold I had a 1/4" nozzle every 6" each was pointed down towards the opposite side where the grates met the side wall. The nozzles went all of the way, from one side of the left door (It had 2 doors) around the firebox to the side of the right door, each blew into the fire. The blower was a high pressure unit with paddles not a squirrel cage, it had good pressure not high volume.
Befoe I did that, after dark I always saw a large ball of fire just above the top of the stack. That was wood gas reigniting as it got more oxygen and not fire traveling the length of the evaporator and up the stack. Doing that accomplished a couple of things, my evaporation rate increased, while my wood consumption dropped. I was then burning the wood gas under the pans and not above the stack where it did no good. I then went from every 7 minutes fueling to every 9 minutes, all by using a timer. My wood consumption fell by about 10% if I recall and my evaporation rate climbed about 15%. Those changes got the flues pan boiling hard, where it had been somewhat poor before that.
Read the article I've made a Sticky in the front of the Evaporator threads. I think you will find, if you do it, that your issues will go away, you will boil faster and use less wood. However, unless you get lucky like I did, high pressure blowers are not cheap, mine came from a factory that had closed and it was free. When I sold that evaporator the whole system went with it.
My new evaporator is being converted to oil fired and is only a 2x6 raised flue.

[Willen]

Thanks all. Flues are clean, the ramp is up to 1” below the bottom of the flues, maybe this should be higher?
I will add another section of stovepipe, but I never have flames out of the stack.
I suspect the main culprit is a combination of being in the lee of the gable of a taller abutting building, and a flip top rain cap, which seems to slightly back pressure the pipe during certain wind directions, as my burn/ draw really varies some days