rballou@mnsinc.com on sun 10 nov 96
Has anyone else had any experience with the double venturi flue design?
I've also read Kirby Benson's post from yesterday. Also, has anyone tried
doing a test firing with a mostly empty kiln? I'd like to get some feedback
on the double venturi flue before I sacrifice a kiln load of pots to the
experiment. My kiln is built so that I can make temporary modifications to
the chimney and flue. My thought is to stack the kiln with enough shelves
so that I could place cones all over and put in a few pots so that I could
read the reduction. I should be able to reach temp quickly, but will it
tell me anything about evenness and reduction effects. Does the kiln need
the mass of the stack for this experiment to give me any meaningful
answers? Anybody have any thoughts on this idea?
Ruth Ballou
rballou@mnsinc.com
>----------------------------Original message----------------------------
>Jim:
>
>Lou's "Art of Firing" is a great book. A wealth of information. It and
>Rhodes "Kilns" and Olsen's "Kiln Book" are the three resources I use
>when designing and building kilns. There is one area of the book I'm not
>exactly sure of. It's Lou's contention that the double venturi flue box will
>work with any kiln design.
>
>As soon as I read "Art of Firing" I was so impressed I changed the exit
>flue and chimney to a soda kiln I constructed. That kiln is a 24 cu. ft. hard
>fire brick sprung arch downdraft. The burners are four "Alfred" type 2"
>pipe burners using natural gas. There are two on each side of kiln with
>bagwall deflecting/dispersing flame and heat.
>
>I reduced the size of the exit flue from the chamber and constructed the
>flue box and stack exactly as specified. It didn't work.
>
>I tried everything: oxidation, reduction, less gas(W.C.I), more gas, longer
>firing cycle, open damper, restricted damper, added to chimney stack. I
>even put blowers on burners, which I had never used before. Nothing
>worked. I fired it three times approximately 20-24 hour firing cycles and
>the highest temperature I achieved was cone 6 barely on the bottom.
>
>I went back to the 9" x 9" exit flue. I did stay with the flue box and stack
>design sans venturi which I think are excellent designs. The kiln works
>great. I fire to cone 7 in about 12 hours. Good even heat, atmosphere,
>and vapor.
>
>Has anyone else out there had a similar experience? I believe the MFT is
>an excellent kiln design. My experience makes me think the double
>venturi flue box only works with the MFT design and IFB materials.
>
>Rafael Molina
>Rmr3431@dcccd.edu
>
>>>> james & becca sydnor 10/09/96 09:45pm >>>
>----------------------------Original message----------------------------
>I,m in the process of building a down draft kiln, about 50cu/ft, 2600
>soft bricks, two forced air burners (about 375,000btu's a each). I have
>most of the design worked out, but I am using the design in the Nils Lou
>book for the burner port size, and most importantly the flue and
>chimney. He indicates that this design and size works well with a
>variety of kiln sizes. I was wondering if anyone has experience with
>this design and if so would that e-mail me about their opinion of the
>design.
>
>Thanks for the info
>Jim Sydnor
Marcia Selsor & Matt Benacquista on mon 11 nov 96
rballou@mnsinc.com wrote:
>
> ----------------------------Original message----------------------------
> Has anyone else had any experience with the double venturi flue design?
> I've also read Kirby Benson's post from yesterday. Also, has anyone tried
> doing a test firing with a mostly empty kiln? I'd like to get some feedback
> on the double venturi flue before I sacrifice a kiln load of pots to the
> experiment. My kiln is built so that I can make temporary modifications to
> the chimney and flue. My thought is to stack the kiln with enough shelves
> so that I could place cones all over and put in a few pots so that I could
> read the reduction. I should be able to reach temp quickly, but will it
> tell me anything about evenness and reduction effects. Does the kiln need
> the mass of the stack for this experiment to give me any meaningful
> answers? Anybody have any thoughts on this idea?
>
> Ruth Ballou
> rballou@mnsinc.com
Dear Ruth,
I fire all the time with double venturi system for the past 16 years.
I have found that a kiln should be stacked tighter in the front,
atll in the rear top, and about 9" across the bottom. I have
a 60 cu ft car kiln, a 48 cu ft hinged door sprung arch and a new
catenary cast soda kiln. The car kiln has three shelves on the
bottom 12x 24" with a 2" space at the front and 1" between the shelves
and 3" in the rear near the flu. The door is set inside with 2" of
fiberfax coated with rigidizer. This kiln has two monster venturi
burners and fires really sweetly with finger tip controls when you
move the damper or adjust the air or gas. Every kiln has a personality
and you must learn how to get along. It takes firing and stacking and
paying attention to the weather conditions, etc. Eventually you'll
become compatible and establish an understanding.
Marcia in Montana
--
Marci Selsor
Matt Benacquista
http://www.imt.net/~mjbmls/
mjbmls@imt.net
Dave and Pat Eitel on mon 11 nov 96
Ruth--
----------------------------Original message----------------------------
>Has anyone else had any experience with the double venturi flue design?
>I've also read Kirby Benson's post from yesterday. Also, has anyone tried
>doing a test firing with a mostly empty kiln? I'd like to get some feedback
>on the double venturi flue before I sacrifice a kiln load of pots to the
>experiment. My kiln is built so that I can make temporary modifications to
>the chimney and flue.
Raphael's experience was totally alien to my own. My kiln is 3 years old,
has about 50 feet of stacking space and has been fired 50-60 times. I used
the double venturi chimney design in Nils' book, and it works fine--just
like Nils says it does. I have no trouble hitting ^10 flat in 12-13 hours.
My feeling that doing a test firing with very few pots in it would not
yield significant results, since there would be not as much mass absorbing
and holding and radiating heat. If you don't want to risk pots, what about
putting firebricks in in theirk place--just standing and laying them around
as if they were pots?
Later...Dave
Dave Eitel
Cedar Creek Pottery
Cedarburg, WI
pots@cedarcreekpottery.com
http://www.cedarcreekpottery.com
Craig Martell on mon 11 nov 96
My kiln is a 66 cubic foot mft ( although I have a 6" rise sprung arch roof).
I pretty much built the kiln to Nils specifications, but the hot face
refractories are k-26 instead of k-23. I use propane and fire with 2 Big
Berthas with 7/64th orifices. I max them at 3psi. I usually use about 45
gallons of gas to reach cone 10 in 12 to 14 hrs.
I also use an Australian Oxyprobe. My experience with the double venturi is
that it works if the kiln is tight and free of excessive air leaks. I found
that the stack draw was less than I wanted until I packed the underside
perimeter of the car with fiber, during firing, to diminish air leakage
there. I also tightened up the body of the kiln by plugging leaks with fiber
and checked the oxyprobe periodically while I was doing this. I left the
damper setting constant (temp was about 2250 F.) and noticed the reduction
values dropping as I progressed with the plugging of air leaks. Of course
this procedure would make any kiln draw better but since I do have a double
venturi I thought it would be worth mentioning.
My advice on test firing would be to fill the kiln with ware. Kilns don't
fire and cool the same partially loaded. However, I wouldn't reccomend
firing a lot of time consuming pieces like teapots or something. Make
simple, faster pieces, if possible, and cut down your production time until
you have the kiln figured out. When you are test firing to find solutions to
problems with the kiln, you want the most accurate info that you can get. If
you fire partial loads and modify the kiln based on these firings you may get
totally different results when you go to full loads. This is only my opinion
based on the way I mapped out two gas kiln. Take it with the usual grain of
salt. I forgot to mention it earlier but Big Berthas are torch heads or weed
burners made by L.B. White Co. Onalaska Wi. They cost $35.00 each.
Kind Regards, Craig Martell-Oregon
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