Back pan won’t boil

[MiMappleMan]

I have a 3x7 evaporator with a 3x3 flat syrup pan and a 3x4 back pan. I had fabricated the arch with the goal of drop glue back pans, so from the bottom of the back pan to the bottom of the arch is about a 7” gap. The whole arch is insulated with ceramic blanket.

No matter what I try, I cannot get the back pan to boil at all. It gets the sap scorching hot, but the most I get is a few bubbles close to the front of the pan. Last night, with seasoned wood split 2” wide pieces, I only had an evaporation rate of around 17 gph, which is nowhere close to what I should be expecting from a rig this size? Any ideas of how to increase that rate to something not so depressing? Would filling in that 7” gap so there’s only a tiny room between the pan and bottom of arch really make that much of a difference?

On a side note, anyone selling a 3x4 drop flue can send a message my way


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[ecolbeck]

You are correct. Increase the height of the ramp so that its closer to the bottom of the pan. Probably a couple of inches would suffice.

[SmellsLikeSyrupNH]

Ive been told to try to not have more than an inch and a half and even all the way to the stack try and make the space as small as possible so that the heat stays on the pan as long as it can before going up the stack.

do you have a blower? Might need one OR maybe its blowing too hard and you are blowing your heat right out the stack.

[BAP]

Under the flue pan, pull your insulation back, then fill it up with Vermiculite or sand, then cap it off with the insulation to hold it in place. Leave 1/2-1” gap between the flues and insulation. That will force the heat threw the flues.

[berkshires]

I have a 3x7 evaporator with a 3x3 flat syrup pan and a 3x4 back pan. I had fabricated the arch with the goal of drop glue back pans, so from the bottom of the back pan to the bottom of the arch is about a 7” gap. The whole arch is insulated with ceramic blanket.

No matter what I try, I cannot get the back pan to boil at all. It gets the sap scorching hot, but the most I get is a few bubbles close to the front of the pan. Last night, with seasoned wood split 2” wide pieces, I only had an evaporation rate of around 17 gph, which is nowhere close to what I should be expecting from a rig this size? Any ideas of how to increase that rate to something not so depressing? Would filling in that 7” gap so there’s only a tiny room between the pan and bottom of arch really make that much of a difference?

On a side note, anyone selling a 3x4 drop flue can send a message my way


Sent from my iPhone using Tapatalk

From everything I've read, you want the space under your back pan to have the distance from the bottom of the pan to the top of the arch below it such that it makes an area the same as the area of your flue pipe.

So assuming for the moment that you have an 8" flue pipe, that's 2 pi r squared, or 100 square inches. To get the same area under your pans, if your pan is 3' wide, that's 36" times a little less than 3". So you have more than double the distance between your pan and your arch that you should.

Cheers,

Gabe O

[berkshires]

Under the flue pan, pull your insulation back, then fill it up with Vermiculite or sand, then cap it off with the insulation to hold it in place. Leave 1/2-1” gap between the flues and insulation. That will force the heat threw the flues.

He doesn't have a flue pan.

GO

[ecolbeck]

From everything I've read, you want the space under your back pan to have the distance from the bottom of the pan to the top of the arch below it such that it makes an area the same as the area of your flue pipe.

So assuming for the moment that you have an 8" flue pipe, that's 2 pi r squared, or 100 square inches. To get the same area under your pans, if your pan is 3' wide, that's 36" times a little less than 3". So you have more than double the distance between your pan and your arch that you should.


Math correction (nerd alert). There was an extra 2 in the formula.
Area of a circle is pi * r^2
For an 8” pipe the radius is 4.
Therefor area is pi * 4^2 = 16*pi = 50ish square inches.
This suggests that the gap under the pan should be just under 1.5”.

[berkshires]

Math correction (nerd alert). There was an extra 2 in the formula.
Area of a circle is pi * r^2
For an 8” pipe the radius is 4.
Therefor area is pi * 4^2 = 16*pi = 50ish square inches.
This suggests that the gap under the pan should be just under 1.5”.

Thank you! I was confusing it with the formula for the circumference, which is 2 pi r. Sorry for the misleading post! Just goes to show I shouldn't try to remember middle school math 40 years later without checking my memory!

So yes, ecolbeck is right, you're off by a factor of four, not just two as I suggested (assuming an 8" stovepipe).

GO