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High Bridge Pottery

Gas Kiln Design

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My friend has this gas kiln that we fired a few days ago, the pots actually came out really nice but the design of the thing is confusing me.

 

It has six burners, three on the front and back side. The flue goes out the bottom at the back but it also has a damper on the top not in the chimney  :blink:

 

I have never seen anything like this before. I am not even sure anything was going out the flue at the bottom. The damper is a flap like thing that you open and close.

 

No idea how we fired it with good results. Started with the flap slightly open and went up to 1000 degOnly closed it slightly to start reduction. If I completely shut it then the temperatures started dropping.

 

It seems strange and I am not sure what the gasses are doing when they go in, I feel they are all exiting through the top of the kiln.

 

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I'm not quite sure what kind of draft  :huh: Yes they are the burner ports on the back with the flue. They are flipped on the front so two on the left and one right. Venturi burners that look a lot like this, not sure about their specs though, and the top two don't work.

 

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It hit cone 10 in about 12-13 hours with us being cautious.

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Its a car kiln of strange design.Have fun as it seems to work well.Never seen an updraft downdraft combo.I would not use the flap on the roof at all. Down draft uses heat and flame more effecently.

Mark

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So it's only firing off of two burners, one on the back wall and one on the front wall, or are the other two burners on the front wall working?

 

Is the downdraft flue open or closed? How tall is the chimney- just to the top of the kiln or up and out the building?

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4 out of the 6 burners work, the bottom and middle ones on the front and back. Downdraft flue is open and has a chimney to the top of the kiln which sits under a big hood that covers both the top flap and the chimney that goes out through the roof.

 

 

I was thinking about the possibility of changing it into a cross draft but closing the top hole and leaving the burners as they are could work. I would probably need to add a damper into the back flue?

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It's a really odd design, for sure. All I can figure is that the downdraft flue is acting as an intake for the updraft. Was there a cold spot down by the downdraft exit flue? Who built it?

 

Maybe Baymore will have some insight.

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The stack is like a Giel kiln (only as high as the kiln)

His kilns are downdraft and are venturi 

I do not know why you would change to a crossdraft as the chimney is in place-just put a damper in it.

how even did this fire?

Mark

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It seemed pretty even but I can't say 100% as there was only cones in one spot. Next time I will get cones all over the place to properly see how it fires. All reduction seemed even across the kiln besides right in the middle. 

 

To make a cross draft I was thinking that it would only involve moving the burners at the back to the front but getting holes in the fibre would be a bad idea. Better to leave them all as they are and add damper to chimney

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If you were firing with the top vent open from the beginning, maybe you never established enough 'draw' through the chimney and the kiln was functioning as an updraft.

I would try one firing with the top closed, using just the chimney damper for control (assuming that it's not blocked, is big enough and long enough to draw properly - Olson's book gives ratio figures). It might be that the kiln has been re-engineered to an updraft because of chimney limitations. My first downdraft had the chimney built into the back, it looked elegant but never got good airflow. Rebuilt with a bigger and longer chimney, even added a galvanized extension, and then it drew properly.

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Close the top vent. It is confusing the draft. Place cones all over esp. at back bottom. Might be a great little kiln. Too early to tell.

You do not want to make a cross draft. Stick with the burner placement you have.

TJR.

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After attempting another firing it turned out the previous owner had blocked the flue. Weird, kicking myself that I never thought to look. Needed to think these thoughts before turning it on. Boneheaded mistake. Not thinking properly as it is not my kiln or studio. Shouldn't have gone with the second firing before looking it over. I do learn best from my own mistakes so noted and remembered  -_-

 

Surprised we are not all dead. All very light headed halfway through firing as we forgot to open the doors like last time. Gassed ourselves bad.

 

Glad to still be here :D not sure how many heavy metals entered my body although I had to leave half way through at about 800 degoC so probably none.

 

On the positive side, I pan roasted some coffee over a fire and it tastes great :D

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Doesn't look like bad design for home built. It's a downdraft for sure. I'd suspect that the designer added the top flue for some additional control over the firing.

Not a bad thing. That, and possibly for candling the kiln.

I'd open both flues and crack the door, peep holes out, while you candle up to about 500-700 degrees, then close the peeps and the door.

This will give you some time to watch it, make sure the burners are working properly, and if one goes out the extra unburned fuel will escape.

 

Once it gets up to 1000 degrees you can star your gradual climb. Shouldn't take more than 8-10 hours to reach ^10 plus some time for soaking (30-60 minutes) and/or reducing if desired.Take notes and experiment keeping in mind slow is better at first.

Take notes each time for gas/flu/air.

My schedule looks something like this, in columns:

Time - Tank % (I use propane) - Gas - Flue -Air - Temp - Notes

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