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.

[wlatrout]

Thanks for the input. I'll be working with it today, trying modifications. Next week looks like good sap weather.

[wlatrout]

Today I changed the air gap under my back pan to a straight 1 1/2 " That gives me 30 in. going to a stack of 28". Next boil will be with sap ..Hoping that will be Mon. or tue. Thanks for the help.

[wmick]

I read this fairly quickly and may have missed it... Probably a silly question, but how deep is your sap in the pans?
Too deep and it will take forever (if ever) to get to a raging boil...

If you still have problems after your next try, maybe try taking the blower off and just let the natural draft work on it?? I really don't have any experience with the fan force draft, but I think it is possible to have too much... forcing the un-burnt gasses out of the firebox too quickly?? Just a thought?

and one more question.... Are the sides of your firebox bricked? I presume so, but its not noted in your sketch. In your sketch the firebox seems quite large for the size of pans.. ... You want to make sure you are reflecting the heat back into the fire, with brick, to ensure full ignition of the gasses.

[wlatrout]

I made and installed a float box, and it is at 1 5/8 " of sap in the pan . The arch is fully bricked and insulated. Yesterday I raised up the extension floor up to within 1 1/2 " of the bottom of the pan. Bought a moisture tester and checked some of my wood supply. It runs from 6% to 14%. Going to get some cutoffs from the cabinet shop to burn with it. Looks like midweek I should try it.

[wlatrout]

One other question I was thinking today is would it be better for the boil process to reverse the pans,with the short pan in front?

[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.

[wlatrout]

Today I made my first sap boil Overall it worked great It boiled much faster then it did before the conversion . Had a rolling boil in the 2 runs on the left side of the front pan , but the right or finishing run boiled but not as vigorous as the other 2. The back pan with a divider running crosswise yust boiled but not hardy. Over all I am pleased. Just need some input on why the rt. front is not as vigorous. Try to keep the wood even across the fire box.

[Cjadamec]

Your draft blower is mounted in the front and pushing the fire towards the back of the evaporator. That's likely why you have a slightly colder spot in the front. You could try looking into how your draft enters the fire box and possibly make a baffle to force the air under the grate and under the fire rather than rise up in front of the fire creating a cold zone by the front wall of the fire box.

[wlatrout]

Thanks I'll try that.