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I'll be in good position to learn more about the contributing factors to reduction.  My next firing will be the second with the oxyprobe.  I'm interested in your experience with venturi burners and adjusting primaries for reduction.  I typically run them in almost to the point of disrupting the flame at the beginning of reduction, 1600F.  One adjustment of gas and damper and then I leave them there all the way through the end of the firing.  The kiln climbs in reduction to cone 10 with only small adjustments to the damper.

I'm particularly interested in whether the primary adjustment really makes any difference.  Without the oxygen meter, I've just been doing it this way because I always have.

 

 

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I never adjust the air flaps.I leave them open and just use the damper-its so much easier.I do this on three of my kilns.

It was taught in art school this way by some Alfred graduates (my instructors) been doing it ever since . I like easy, the damper is your friend thats why its there, Much easier.

Edited by Mark C.
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13 hours ago, CactusPots said:

I'm particularly interested in whether the primary adjustment really makes any difference.  Without the oxygen meter, I've just been doing it this way because I always have.

 

Best way we have found to get maximum performance from these very burners was to set all air shutters equally at  half open or better and begin your fire. At body reduction time, Set reasonable gas and push into body reduction with the damper. Once in this mode with a consistent reading on the oxyprobe adjust each shutter 1/2 turn at a time for least amount of reduction on the oxyprobe. At this point these will have the maximum back pressure on them and adjustment of the primary air shutters will be super sensitive. Maximize the flow at this point which will minimize the reduction. Takes maybe 10 minutes .... and you are done ever moving these. (Mark them, jamb nut them)

Fine tuning these at this point maximizes  the efficiency of the burners and allows one to have the greatest power available through the firing as well as use the least amount of propane. For reduction using Venturi burners ........ gas and damper are The primary tools. Hyper tuning your primary air shutters Provides more available power at the top end of the firing should you need it. No better time to get this set As you note during ordinary firing turning these many turns in either direction seems to have no real effect.

Since these are venturis you will need to pick a best gas pressure to maintain a full volume reducing atmosphere in the kiln to minimize dead spots and some damper closure for desired reduction.  Unwanted air that enters and does not get diluted by the reducing environment is available oxygen capable of erasing your reduction. Strong flame from the sight ports will show just how pressurized your kiln is, especially the lowest port as there will be a pressure gradient from top to bottom in the kiln.

Experience will dictate the best gas damper position  (Referring to sight port jet size and oxyprobe reading) and for propane -  body reduction (high numbers .7-.8) probably will be difficult below 1600 degrees. For natural gas, this is probably closer to 1500 degrees. Never start any sooner than the self ignition temp of the gas being used so 1500 is probably absolute minimum.
 

Edited by Bill Kielb
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Once in this mode with a consistent reading on the oxyprobe adjust each shutter 1/2 turn at a time for least amount of reduction on the oxyprobe. 

If I'm expecting the reduction to drop (?)with this fine tuning, then I'm adjusting the primaries out?  The working assumption here is that the ideal position for the primaries is something greater than 50% open?

I was thinking to run the primaries all the way in the way I have been doing and then evenly adjust them out to see what happens.   I'm guessing that as I adjust them out, there will be a point when going any further effects no change.  That would be the optimum point?

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2 hours ago, CactusPots said:

f I'm expecting the reduction to drop (?)with this fine tuning, then I'm adjusting the primaries out?  The working assumption here is that the ideal position for the primaries is something greater than 50% open?

 

What we have observed is: Not necessarily, but start at full open or nearly closed if you are concerned. What you should notice is there is an ideal point where the reduction decreases as whatever little air flow passing that disc becomes more orderly, more laminar and more efficient for that burner at that pressure. It appears to be much easier to fine tune while the back pressure from reduction  on the venturis Is present and can often increase the reduction as the shutter is opened  further, go figure! So we have found it easiest to just adjust while in its most sensitive mode since you have the oxyprobe to guide you. I should add once this point was detected on one burner, then all were adjusted to be similar with more fine tuning from there. It has been fairly dramatic in our experience so pretty easy to get them optimized.

Edited by Bill Kielb
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One thing I should have added is since I bisque in my large car kiln about 99.9 of my wares I did adjust my air flaps to the optimum neutralizing atmosphere . I just leave them there during all firing. The damper on the down draft and my updraft does the reduction .

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  • 2 weeks later...

It doesn't appear any adjustment to the primaries makes an impact on the reading of the oxyprobe.  At my normal setting, I reach reduction temperature at 1600 with an oxy reading of 31.  My usual setting for reduction at that point reads 81  The kiln climbs about 100 degrees or so for the hour of heavy reduction with the bottom eventually passing the top (down draft).  Maybe it just doesn't matter.

I should watch and see if Geil ever does another firing workshop.  My kiln is more like his that any other.  Since it's a homemade job, maybe there are peculiarities.  

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49 minutes ago, Bill Kielb said:

Definitely telling you something if you can adjust your primary air fully closed and get no change dont you think?

Not cinched down, just to a few mm.  What would you say it's telling me?  I would guess the burners are able to draw all the air they want from the gap between the burners and the floor.

I'll have to get back into my kiln building reference books and see what the gap is supposed to be. 

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51 minutes ago, CactusPots said:

I would guess the burners are able to draw all the air they want from the gap between the burners and the floor.

About 50% of the air comes in as primary air as a result of the gas velocity shooting through a Venturi and 50% comes in around the burner penetration. I don’t know whether to question: the reading, the primary induction into the burner, the burner penetration, if the kiln was in reduction sufficiently with the damper ........  This kiln doesn’t increase draft with a taller chimney, it seems to defy physics in many ways. My conclusion I would need to spend a few hours firing with you or watching this happen to understand  how and what to test.

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As Bill says 50% comes thru the burner so if that is cut off the rest is what is called secondary air and you still have plenty (my burners have the same deal-tons of secondary air).

So cranked down air flaps do not move your meter numbers at all??

what are you doing to reduce kiln ?

A- turning up gas?

B- moving in damper?

something else?

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A-  Turn up the gas  From about 4" at 1600 to 6" the rest of the way

B- the damper in by about half.

Slight adjustments to the damper (1/8" per) to get temperature rise to finish.

I had a suspicion the primaries adjustment wasn't making a contribution to reduction.  Now I want to know why. 

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41 minutes ago, CactusPots said:

Now I want to know why.

Here is one we just finished fine tuning. Geil I think, propane. Works like a charm. Pictures of close up of burners and penetration as well as imbed depth. Notice air shutters adjusted positions. This was pre-tune. After fine tune in reduction these ended up about  1/2 - 3/4 closed to get the oxidation fine tuned or to its maximum oxidation. Wide open did not produce the best  amount of primary air. Added pic of upper sight port at early reduction / tuneup time to give you a sense of how pressurized this kiln is during adjustment.

64F7E319-5EDF-4172-A036-1E02739FBB60.jpeg

92691BF3-1882-40ED-9D85-1F4EFAB0B40C.jpeg

C9EC1C8F-CA97-4FFB-83A0-E9A7A926D921.jpeg

Edited by Bill Kielb
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Late to the party as usual... I fired a big 6-burner natural gas Geil for a number of years at the college (before they built us a new art building with 2 Bailey power burner kilns). We set the primaries at the thickness of 2 popsicle sticks and never touched them again. You need some primary air coming through the venturi to mix with the pressurized gas coming out the orifice for good combustion as it exits the burner. With closed primaries, you are just shooting a stream of gas into the kiln hoping it finds enough air from somewhere else before exploding. From here, reduction is achieved solely with the damper. A fuel kiln operates on the flow of the flame being pulled through the kiln by the suction of it exiting up the chimney. If you damper the chimney, not as much exhaust can go out, so there is not as much suction bringing secondary air in around the burner openings while the same amount of gas is coming through the burner. Reduction. Open the damper, more suction from the heat going up the chimney, more flow through the kiln, more secondary air being pulled in around the burner while the same amount of gas is coming though the burner. Oxidation. We found with that kiln that plus or minus 1/8" from 3" opening of the damper was enough to manage the reduction while still managing a moderate temperature rise.

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11 hours ago, Bill Kielb said:

Here is one we just finished fine tuning. Geil I think, propane. Works like a charm. Pictures of close up of burners and penetration as well as imbed depth. Notice air shutters adjusted positions. This was pre-tune. After fine tune in reduction these ended up about  1/2 - 3/4 closed to get the oxidation fine tuned or to its maximum oxidation. Wide open did not produce the best  amount of primary air. Added pic of upper sight port at early reduction / tuneup time to give you a sense of how pressurized this kiln is during adjustment.

64F7E319-5EDF-4172-A036-1E02739FBB60.jpeg

92691BF3-1882-40ED-9D85-1F4EFAB0B40C.jpeg

C9EC1C8F-CA97-4FFB-83A0-E9A7A926D921.jpeg

Bill,   On this third picture,  I see the burner penetrating the floor of what?  This is not the floor of the kiln, I don't think.

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2 hours ago, CactusPots said:

Bill,   On this third picture,  I see the burner penetrating the floor of what?  This is not the floor of the kiln, I don't think.

It is the fire brick on the bottom of the kiln.
Geil over cuts the fire brick and has a shelf or hard brick on the inside which is about 1/2” smaller. You can see this when you reference both top and bottom pictures. For burner entrance it’s usually desireable  to have a cone shaped port within which to inject the fuel gas. I would need to look up the recommended slope but it’s likely 30 degrees or more so secondary air can easily enter as needed. The overcut on the bottom of the Geil likely provides sufficient clearance and the smaller top opening  provides the contraction if you will. It’s easier to design with square openings so likely they tested this arrangement and it performs satisfactorily for them.

The third picture is simply a snapshot of the upper site port (healthy flame)  at body reduction time when fine tuning the primary air is most sensitive to adjustment.

Edited by Bill Kielb
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___________________________________________________________               __________________________________

__________________________________________________________               ________________________________     Brick floor of kiln

                                                                                                                What is the space between the bottom of the brick floor of the kiln and the top of the burner?  

                                                                                                                    ---------   top of burner

                                                                                                                   |                |    

and why does this double space with the return key?

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7 minutes ago, neilestrick said:

The Geil burners have ceramic tips, correct? For all metal burners I would not have them extend into the brick opening.

They do, but so do his actually, from his picture above anyway. The Geil burners extend into a pretty decent overcut which is sized down at the kiln entrance. See pic above.

Edited by Bill Kielb
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6 minutes ago, Bill Kielb said:

They do, but so do his actually, from his picture above anyway. The Geil burners extend into a pretty decent overcut which is sized down at the kiln entrance. See pic above.

Just clarifying for future readers. And I was too lazy to go back and see what type of burners he's using.

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Some of the information I was able to gather yesterday's firing.

At 1600, which is where I would normally start reduction, the kiln is already registering about a 34 on the oxyprobe,

My gas and damper settings for reduction run it to 80

The kiln will climb to finish, very slowly at the end, but very even temperature top to bottom.  It will register a lower oxyprobe number as it goes by itself and I usually make a few small (1/8") adjustments to the damper to move things along.  Pretty consistent 12 hour firing.  Soft 10  Oxyprobe number at finish was 485  36 cubic foot kiln used 25 gallons propane

Correct me if I'm in error, but my take away is that the primaries are largely irrelevant for reduction firing. 

I prefer to bisque in the electric kiln, but if I was to use the gas kiln, that would be another set of questions. 

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3 hours ago, CactusPots said:

Correct me if I'm in error, but my take away is that the primaries are largely irrelevant for reduction firing.

Yes, that was our experience, and why once we set the primary disks we never crawled under there again. But at the same time, I have seen uBoob videos of peeps firing their gas kilns with more easily accessible rear mounted burners go about tweaking the primaries during reduction as if that's what they think (or were taught somewhere) is the thing to do.  And then they jam the damper in until great clouds of black smoke come belching out the stack. Another thing that is unnecessary.

cheers,

dw

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At 80 on the oxyprobe I have a distinct gas odor.  Not black smoke, but the exhaust is visible.  I always adjusted the primaries to less than a quarter inch at reduction because I thought, but had no way of knowing that cutting the primary air would increase reduction.  Mine are at least accessible, the kiln is open on both sides.  The West Coast kilns that I learned on were not accessible.  That was a long time ago.

I really have this kiln down to the basics for firing.  I don't know where to go for any improvements, but my personality won't leave it alone. :) 

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