Thoughts on getting boil in flue pan evened out

[MN Jake]

We have a 2x2 syrup and 2x8 drop flue. Front end of flue pan boils violently compared to the other seven feet. I'm sure that's somewhat normal but it seems to be affecting the float (inlet tube from float comes up close to the front). Basically I believe the uneven boil is causing a current that pushes back into the tube causing the float to perceive its full. We have been shutting the valve between the pans during firing to prevent surging and it works, getting fairly consistent draws although we'd like to eliminate that detail. We have kinks to work out with the stack and fire door and other minor details but would arch paper pinched between the pans solve that? Possibly dropped a couple inches down the front of the flues or is it other issues?

[Buddy 58]

I learned along time ago to build baffle walls with fire brick under my rear pan ( 3x7 ) flue pan raised flue . I leave about a 2 inch space between brick and flues . I have two separated by 2 & half feet - fire rolls up and over twice before the stack . No preheater , with good firing I get full rolling boil entire length of pan . Maybe this will be helpful to some of you .

[MN Jake]

I learned along time ago to build baffle walls with fire brick under my rear pan ( 3x7 ) flue pan raised flue . I leave about a 2 inch space between brick and flues . I have two separated by 2 & half feet - fire rolls up and over twice before the stack . No preheater , with good firing I get full rolling boil entire length of pan . Maybe this will be helpful to some of you .

I understand where you're going with that on a raised flue but the flues in my unit start right at the back of my firebox. So if I build a wall I would be forcing all the heat directly thru the start of the flues and would make the front end even hotter. I was told multiple time by several people to slope progressively tighter to the back. Not really sure what's right in this case.

[Buddy 58]

Sorry , didn't see you had drop flues in your display , I have run both styles and the only thing I know with drop flue is yes ramp it up good and fire !

[motowbrowne]

I think a video would be helpful in this case. My previous cooker ramped gradually from the firebox to the bottom of the flues. That one happened to be a 2x10. It boiled very hard up front, and not vigorously in the back, but it still boiled all the way to the end of the 8' flue pan.

My new cooker ramps very steeply up to the bottom of the flues. There may only be a foot or 16" of flue pan that allows the flame to enter the pan (raised flue). From there the arch is full to within an inch of the flues until it starts to ramp back down about 4' from the end of the pan. I've heard of people doing what Buddy 58 is talking about, but I've never tried it. My new rig boils very very well set up the way I described. I like the idea of making the heat go into the flues and stay there. It doesn't do you any good 4" below the flues in the arch, is my thinking.

The crazy boiling in the front is what you want. You don't want to have to slow that down. If it's interfering with your float, perhaps Jim would have some ideas for you. I know that on my old 2x10 there was a little deflector thing that made it so the sap filling the float box was calm, not surging from the boil. Perhaps you could do something like that. Another tip, I haven't seen your arch, but if you're getting a noticeable surge or rather lull from firing, try to fire quicker. Get the door open, get your wood in and get the door closed ASAP. Hopefully 20 seconds or so on a rig that size. If you have two doors only open one at a time. This will help reduce the temperature peaks and valleys inherent with a wood cooker.

Good luck, I hope you get it figured. Opening and closing the valve all the time sounds like a pain, and if you forget to reopen it once it could be bad.

[MN Jake]

Yes, we are trying to fire quicker but son of a gun it's hot when you open that door. Welding gloves help a lot but any exposed face cause me to back away for a second or two. Anyone try a chainsaw face shield or anything to help with that?

[motowbrowne]

Yes, we are trying to fire quicker but son of a gun it's hot when you open that door. Welding gloves help a lot but any exposed face cause me to back away for a second or two. Anyone try a chainsaw face shield or anything to help with that?

I've never used one myself, but I saw a video clip of someone firing a big rig with a clear face shield. I think that'd be preferable to the wire mesh ones. I bet it'd be nice. I know that when I've been cooking for several hours my face feels sunburnt. Door open and closed in the absolute minimum of time is paramount to getting your rig to run right.

[MN Jake]

Thank you, I respect your advice

[Sugarmaker]

Jake,
The mask might work? Sounds like you have fire in there to get a boil. How much stack do you have?
How deep are you boiling?
I would not recommend shutting off the valve between the pans!
On the sap tube coming to the front. Are you having the one open opposite the side going in to the front pan?
How often are you firing?
When you say surging at the float box what is happening?
Regards,
Chris

[MN Jake]

Jake,
The mask might work? Sounds like you have fire in there to get a boil. How much stack do you have?
How deep are you boiling?
I would not recommend shutting off the valve between the pans!
On the sap tube coming to the front. Are you having the one open opposite the side going in to the front pan?
How often are you firing?
When you say surging at the float box what is happening?
Regards,
Chris

Chris, we are running about 1 1/2" deep. Ran lower before but temp gauges were moving up and down a lot until we deepened it. Seemed to go away at an 1 1/2. Probes have always been a fuzz off the bottom of the pan. I have 17' of stack. I do need a couple more feet. I have same side reverse, all valves are properly open or closed to where we are drawing. The problem is the front end of the flues boil so violently it causes a current that rushes to the back. The float is in the back and the incoming sap is fed thru a stainless pipe laying in the boil which outlets a foot or so from the front of the flue pan, it is opposite of the side that runs to the syrup pan. The current forces sap up the pipe causing a surge when we open the door to load. (Boils settles down current stops and float thinks it's low in the pan)We load it get the door shut and about a minute later our syrup probes start dropping a couple degrees. The valve we were temporarily shutting is the feed from flue to syrup pan to prevent it from mixing to terribly.

[BAP]

If you have a 2x10 evaporator, you need at least 20' of stack to get good draft unless you have a AUF blower. If you don't have a blower, then you may not be getting enough draft sucking the heat to the back of your pans which also could be why it is so hot when you first open the doors. How much space do you have under your flues after the ramp? 1/2"-1" is plenty. Don't worry about the up and down in the flue pan float box as long as the sap stays at the correct depth in the pan.

[MN Jake]

Yes I need more stack. It is 12" so I don't think we're lacking on size but I need a couple more lengths. I'm not much more than an inch away after the ramp up. Do you guys use something that holds heat like sand or brick? Or just purely vermiculite or cer blanket under the flues?

[warners point]

Jakes

How wide is your stack at the base? It should 2 feet wide so your pulling heat across the entire width of your flue pan. You also need to lengthen your stack to improve your draft.

[MN Jake]

Jakes

How wide is your stack at the base? It should 2 feet wide so your pulling heat across the entire width of your flue pan. You also need to lengthen your stack to improve your draft.

It does widen to almost an inch from the sides. About 22" wide