Remade evaporator.

[wlatrout]

I posted earlier about my changes. I can't get to a boil. If someone could look back at that post with the pictures [I couldn't get then rotated] and give me some ideas .I would be forever grateful. Thanks in advance .

[ecolbeck]

My ideas are:

1. Fire isn’t hot enough. Your previous post mentioned stack temp of 500 degrees. See if you can crank it to 900. Make sure your wood is well dried, etc.
2. Based on your drawing there may be too much space underneath rear pan. Reduce the space to 1.5-2.0 inches and see if that helps.

I would not try to block off the stack opening with bricks. Attempts to block the flow of flue gasses with dampers etc, are misguided. You do, however, want to push those flue gasses up against the bottom of the pan as much as possible.

[Cjadamec]

Lots of things going on there.

What size stack do you have going out your roof? If its a 6" stack you are going to want to bring the air gap under the entire back pan to be around 1-1.5 inches. An 8" stack would be 1.5-2.5 " of air gap. Don't worry about the opening in your transition piece its the air gap under the pan that makes all the difference.
Are you using clean dry seasoned wood? Is it split down to wrist size pieces? Are you building the fire big enough? You are looking for 600+F for stack temps. Is your blower fan big enough?
What part of the pan/s isn't boiling? The whole thing or just the back pan?
Are you doing anything to pre-heat your sap?

[wlatrout]

6" stack through the roof. wood stored inside from last year. 2 1/2 " at front of back pan and 1" at back of back pan. Exhaust opening is 3" x 20". Is that too much opening going to the 6" pipe?

[ecolbeck]

Its possible that a 1" gap under the pan is too narrow. The area of the opening should be approximately equivalent to the 6" stack area.

I think that the exhaust opening size is irrelevant.

See if you can get a rip-roaring, face melting fire going and see what happens.

[Cjadamec]

The Gap under your pan sounds like it is correct for a 6" stack. You are looking for 28 square inches of air space or slightly larger when you multiply the wide of the arch by the height of the air gap.

What does the smoke coming out of the stack look like when you try to get a really hot fire going? All the signs are pointing to a fire that is isn't big enough or hot enough. I would start looking into if you are feeding enough air into the fire and feeding the fire enough wood.

[Keitha333]

Looks like it things should be fine with your design, I would focus on your airflow. It either isn't getting enough and can't get hot enough or your fan is blowing too much and blowing the heat out the stack.

[wlatrout]

Thanks for the reply.

[maple flats]

I wonder if the slope you have under the rear pan should be all of the way to under the stack base? On every evaporator I've had (3 over the years) that space pushing the heat up ended a few inches (3-5") before the stack base. All of my evaporators had a very hard boil, with or even without a blower. I suggest you try removing that ramp at about 3" before the base stack begins, at that point have it drop down about 6 or even 8". Be sure to have brick under that lower area too, to protect the arch floor.
How are you reading the stack temperature, with a probe in the lower end of the 6" stack or just using a surface mount, or a IR non contact on the base stack?
I suspect in your attempt to push the exhaust out you are squeezing or restricting it right under the base stack.

[wlatrout]

Dave, The restricted area goes to the stack base. I will go back in and drop it down and see how it reacts. I am using a non contact temp. reader.