New Forced Air Evaporator

[1951oliver88]

I would like to build a new forced air Evaporator with AUF and AOF. Would anyone be willing to share their experiences and maybe answer these questions-

1. How large should the firebox be? - 2'x6' Arch

2. What have people used for blowers?

3. Anyone have a good door design including latch and hinges? Pictures or drawings would be great.


Thank You

[mol1jb]

Here is my 2x6 build with AOF/AUF: http://mapletrader.com/community/showthread.php?30942-2x6-Raised-flue-Arch-build/page2

To answer your questions
1. For AOF and AUF build I believe 2/3 the length of the arch. My firebox is 4ft long and as wide as the arch minus insulation and fire brick

2. Any high pressure blower will work. A cheap way to go is a bouncy house blower. I have had 2 seasons on mine and it has worked great.

3. Doors can be as simple or complex as you want. There are good pics of mine in the build thread.

Let me know if you have more questions on the build and I will answer as best as I can. One of the best places to start is knowing exactly how large your pans are so you can make all your rails to fit the pans exactly.

[maple flats]

For a 2x6 a 4' firebox is more than needed. My 3x8, factory built has a 3' deep firebox, I think most 2x6's will have about 26" to maybe 30" long fireboxes.

[Ghs57]

I can say that 18" is too small. I intended it to be 24", but forgot to allow for the insulation and fire brick. When I rebuild in the off season, I want at least 24" front to back in the chamber. Surprisingly enough, my small firebox works extremely well. The problem is in loading wood. Everything has to go in diagonally, and when you are running AUF/AOF, you don't want the door open any longer than a second or two. So tricky loading slows you down. And unless you are wearing gloves, risks burning the backs of your hands. Definitely will remove the hair. So, I agree with Dave.

EDIT: I forgot to add the bouncy house blower works great. It's outside in a plywood box, so not heard inside. I also used cast iron barrel stove door (insulted on the inside). Cheap and easy, and holding up well.

[mol1jb]

For a 2x6 a 4' firebox is more than needed. My 3x8, factory built has a 3' deep firebox, I think most 2x6's will have about 26" to maybe 30" long fireboxes.

Like everything there is varying opinions. I reread several older posts on firebox size and found some say firebox size should be 2/3's for gasification arches (AOF) and others say you don't need that much. And I have heard success on both sides.

In general theory of gasification arches you need a good sized fire box for everything to mix (gasses and incoming oxygen) and achieve complete combustion before they leave out of the fire box and go up the stack.

In my opinion it would be better to build the arch frame for the fire box on the large side and if you want to reduce it add more insulation and fire brick.

[1951oliver88]

Maple Enthusiast- how many gallons per hour are you able to evaporate?

[RileySugarbush]

My arch started life as a 2x6. It has since been stretched to a 2x8. Like others, I made the firebox a little short. It is about 20" deep and I wish it was 24. I should have stretched it on the front end and fixed that, but I didn't.


I agree that a bounce house blower is a good idea. Cheap, kind of quiet and reliable. 8" h2o pressure. Mine has been working fine for many years. It works better and is cheaper than the Dayton radial vane blower I replaced. I put mine in an enclosed wooden box so that it is a little quieter and I can shut off air quickly and completely with a simple inlet flapper. No need to mess with a power switch.

There are many ways to arrange the air system. I use a common outlet for over and under air. The under air doesn't require much pressure so I run that out of the blower and through a blast gate that throttles is desired flow rate. Over fire air is routed without throttling to a manifold that wraps around the firebox. The manifold has lots of cross sectional area so there is little pressure loss by the time it gets to the jets. There, the flow is limited by orifice size. I have 12 jets of about .25" diameter. At 8" of pressure, the jets are around 80 mph so give good mixing. There are some things I plan to change, but as it is, we evaporate at 60GPH and used about 1.2 full cords of mostly hardwood to get over 50 gallons of syrup on 3% sap.

[DocsMapleSyrup]

I built a 2x8 AUF/AOF (page 20 "2x8 arch build"). Photos and Firebox measurements are listed there. My fire box is 54" long. I followed the 2/3 the total length of the pan set but backed off to 54" once I layed out the arch on the floor. I believe I could have cut back another 6"; however, much shorter and I would be throwing wood into the drop flues. Remember to figure in your insulation and fire brick when determining the inside measurement of the firebox. I too use a 1 HP Koala bounce house blower and split my air between the AUF/AOF by using a blast gate and cutting down the AUF and let the rest go to AOF. I used 3/8" black pipe for my AOF outlets in the firebox and capped them and then drilled the caps to 1/4". I get a nice burn and keep my stack temp at 750-900 degrees. I can boil 80 GPH but have a hood and preheater

.

[TimJ]

...

3. Anyone have a good door design including latch and hinges? Pictures or drawings would be great.


Thank You

I made a small arch to use at the end of our season instead of chasing with water in the 2x6 we have (mostly I was looking for an excuse for a first welding project)

I have some pics of my door
Someone responded to me - since I had the same question about a door design

See this thread

http://mapletrader.com/community/showthread.php?33494-2x2-build-Looking-for-fire-door-and-stack-transition-plans-pictures-descriptions

A cam lock door is the best way to go IMO
Having used one on a Leader 2x6 arch before we moved to oil.

I might be able to find other pics for you

Here is a Leader arch and door - note that the handle for the cam lock does not cross the door to the frame as someone else posted in one of their pics - the cam lock is what holds the door in place - the handle just has to be set in position to keep the lock in place

19964

My build:

19965

19966

19967

19968

I bought a cam lock trailer door kit from etrailer.com

Something like this
https://www.etrailer.com/Enclosed-Trailer-Parts/Polar-Hardware/383200.html
You have to buy some 3/4" black pipe and weld it up

[TimJ]

There is a limit to the number of pics in one post - so here are two more in a new post

19969

19970

[ennismaple]

For reference: The fire box in our Force 5 (14 feet of pan in total) is about 6 feet from the inside of the door to the back of the box. We need to leave 12" from the door to the front of the wood to allow for air flow and you want space behind the sticks for air flow and to keep them from slamming into the fire brick.