So, Whats the deal with the ramp?

[HyeOnMaple]

I'm in the middle of cutting and fitting my franken-arch and I wondered, what's up with the ramp?
Why are all the professional arches designed with a gradual rise from the fire box to the end of the last pan?
Does it not serve the purpose as well if not better to send the fire straight up to the first (last) pan in the que, and then let it travel close to the pans the rest of the way down to the stack?
Or do I not want to have that much direct fire right under where I will be drawing off?
Or is it some other reason?

Thanx,

[Starting Small]

It is to get the heat to touch as much of the bottom pan as possible instead of the heat leaving the stack without actually touching the pan which does us no good.

[spencer11]

and if you have a raise flue(drop flue to) pan it helps push the flames/ smoke up into the flues

[wiam]

The new high output arches have a straight up wall at the back of the firebox.

[maple flats]

My arch, with High Pressure Air Over Fire has a wall straight up to about 5" below the pans, then a short ramp up to even with the bottom of the raised flues (less 1/4"). I tried going higher by 2" at one point but the boil was so violent directly above that area that the resulting geysers shot so high I lost a large amount of sweet into the hood drain channel. Then I lowered the wall 2 inchest and got much better performance, with a more uniform boil in the entire flue pan. I think I had too much of a good thing.
If you were to look at my arch from the outside you might think the ramp was about 30" long, starting just about 6" above the grates. In fact it is only half that length and it starts about 12" higher.

[LukeDawg11]

I think Mark was asking why not have the ramp start closer to the front pan rather than concentrating the flames at the back. Is there a reason not to have front pan get too hot?

[RileySugarbush]

My 2x6 drop flue has a home built arch with AOF and now ramp. Straight up to even with the bottom of the flues. That wall is still under the syrup pan since it is an old half pint pan at 33" It drops down to an inch below the flues for the rest of the arch. Works great! It even worked good with only AUF when first built.

I think a ramp is more important with natural draft.

[Stamford sugarmaker]

When you say "natural draft" do you mean no blower?

From what I have seen, unless you do not have access to electricity the blower is almost essential for maximum efficiency.

What is the thinking on this?

Peter

[spencer11]

When you say "natural draft" do you mean no blower?

From what I have seen, unless you do not have access to electricity the blower is almost essential for maximum efficiency.

What is the thinking on this?

Peter
yeah he means no blower, i dont have a blower on mine(not enough $$ for this year) but i had my ash door open fully and had a huge draft

[RileySugarbush]

When you say "natural draft" do you mean no blower?

From what I have seen, unless you do not have access to electricity the blower is almost essential for maximum efficiency.

What is the thinking on this?

Peter

Natural draft = no blower. Stack draws air through. The ramp may be more important to make that work well. Years of empirical design has cause the ramp to evolve on the arch design.

With the addition of forced draft, the whole situation changed.

My opinion :

AUF = higher output, higher wood consumption. Efficiency not changed much in terms of wood per gallon of syrup.

AOF = Higher rate and higher efficiency.

[backyard sugaring]

I could be wrong, but i believe the ramp forces the heat up onto rear pan. The front pan should be plenty hot being under the fire box. Good luck to all of you. Lee

[TerryEspo]

What is AOF ?
Last week I had to ask what AUF was, now I will be confused if AOF is air OVER fire. I thought the air had to be under the fire to be efficient ??? I am so confused !!:confused:

Terry

[weekendboiler]

you got it aof = air over fire

[TerryEspo]

Oh grrr. Can someone tell me then some people signature says they have both AUF and AOF. How is that possible ?

Terry

[weekendboiler]

I personally dont have either but a friend of mine has both his aof is mounted on the door (used for loading wood in) and the auf is mounted under the arch on the backside of the ash drop.

[HyeOnMaple]

So, if I just go in 24" and then straight up, add a little AOF, and keep the flame tight to the rest of the pans, I should be in good shape?

[RileySugarbush]

Short explanation:

AUF helps burn wood faster. Just like blowing on a fire. The fire is hotter and burns more wood while boiling faster. It is a great first step in increasing your evaporation rate.

AOF is something entirely different. When wood burns, combustible gasses are created and if there is not enough oxygen, they go up the stack unburnt. If you have a good natural draft or AUF this can be pretty dramatic. Have you ever seen that turbo/afterburner affect at night at the top of your stack? That is the hot unburnt gasses reigniting when they hit the oxygen in the fresh air. It is a waste to burn them up there!

AOF introduces just the right amount of oxygen right above the fire so the gasses burn more completely right there and the extra heat is available to evaporate water. But there is a trick. You can't just open a vent and let air in over the fire. That extra slug of cool air won't mix and burn the gases, it just cools part of your exhaust and reduces your boil. Try running a well set up natural draft arch with the door open and you can observe that cooling effect.

The trick is to get just the right amount of oxygen introduced right above the fire and mix it really well to get the gasses to burn right there. AOF uses high pressure blowers, usually at least one HP, and small nozzles to jet high speed air into the area above the fuel. It's touchy. My first attempt didn't do anything but make noise. Properly set up, you get improved fuel efficiency along with increased evaporation rate. My set up now uses 16 nozzles with about 3/8" openings and the air shoots out of them at about 80 MPH. But only about 100CFM. It works well, and we get good rates of evaporation and use less wood.

[HyeOnMaple]

The trick is to get just the right amount of oxygen introduced right above the fire and mix it really well to get the gasses to burn right there. AOF uses high pressure blowers, usually at least one HP, and small nozzles to jet high speed air into the area above the fuel. It's touchy. My first attempt didn't do anything but make noise. Properly set up, you get improved fuel efficiency along with increased evaporation rate. My set up now uses 16 nozzles with about 3/8" openings and the air shoots out of them at about 80 MPH. But only about 100CFM.

John, Is there a prescribed pattern for the nozzles? are the nozzles anything more than 3/8 nipples welded or screwed into 1-1/4" pipe? isn't it still a cold block of air coming into the box anyway?

Thanx,