kiln operation. DD12 Olympic natural gas

[Mudfish]

Hello all... I have recently acquired a DD12 Olympic kiln. It is properly installed to natural gas in my studio and it also operates with a Bartlett controller. I have fired it at about 3/4th full recently and I have some questions about reading the gouge and what numbers I should be looking for. I had the gas valve set to maintain at number three on the kPa guage. Now that I have looked up a conversion on kPa to water column inches, I see that this valve setting provided about 13 inches on the water column. For natural gas that is too high, right? I know that it should be at 7 inches water column.  I have two questions..,maybe more but here goes. Is 3 kPa's  maintained throughout the firing why my kiln fired hotter on top that on the bottom, or is that from some other issue? I have read on the Olympic website that the primary air plates should be opened up more to bring temp up on the lower level.  My second question is should the kPa reading (converted to water column inches) be steady at 7 inches, or is that a maximum to build up to? The kiln did fire without any error readings from the controller, so I thought everything was going ok during the firing, until kiln cooled off and I could check the cones and discovered the uneven temps. I was firing to cone 8, and cone 8 was bent halfway on top, while cone 7 on the bottom level was barely bent. The spy holes are so small that it is very difficult to monitor a cone pack because of the thick kaowool on the door where the spy holes are, so I am kind of firing blind. Any advice would be greatly appreciated. Thanks 

Edited June 30, 2022 by Mudfish

[Mark C.]

a few questions

is this new kiln with natural gas offices ? Or a used kin that was hooked to propane before ?

Most natural gas is piped in at 1/4 pound or 7 inches on manometer 

is the kiln pipe a 1 inch size as recommended ?

If yes to all these  questions-(no propane orfices which are smaller than natural gas) I'm wondering how you are getting 13 inches of gas presure?

can you address this as its near double what most homes are?

No need to fire blind you need good kiln glasses and move the cones a bit further in in a small spy hole situation  with a soild brick or clay backstop to help see the cones.This is leraned skill set a small laser pointer can also aid it this.

To even the kiln out  temp wise the stacking is the thing that will control the evenness  the most.

In terms of full on with the burners it should not be necessary to have them full on. I would work up to about 3/4  on and let it glide up. The damper setting is whats critical in reduction downdrafts such as this kiln. When in reduction the flame should lick out the botton spyplug a little now and then during heavy reduction

Reduction will aid in evening temps and the stack will help as well

was the lower shelves tall or small pots? was the top tall or small pots

You say 3/4 full where was the empty zone?

How was the flue exit area packed loose or tight?

I set the air plates to one postion and fire with no changes on all my kilns

for me to help I'll need more info 

I sent you a pm which may speed up the fix

Please fill in more details to aid us helping you

also are you new do downdrafts or an old hat?

[Bill Kielb]

9 hours ago, Mudfish said:

I have recently acquired a DD12 Olympic kiln. It is properly installed to natural gas in my studio and it also operates with a Bartlett controller.

Lots of questions here. First do you ramp up the pressure by hand from beginning to end? In essence what is your firing schedule. Second a Bartlett control is an on off controller so I don’t understand how this works unless it’s a soak or high limit only, but that doesn’t explain how you fire. Most gas kilns need to be tended and the gas pressure raised and damper managed, are you doing that? 3 Kpa is 12” wc which is high. What size are your orifices in the kiln at present so we can determine the maximum intended operational pressure. Slower firing will make things fire more evenly, what schedule are you firing to?

Looking at the dd12 literature, 7” Wc is the max pressure, 9/64 is the nat. Gas orifice, 6 burners total 300k btu @ 7 inches wc. You still must manually control your segments firing rates and damper even with an on/off controller especially below 1500 degrees.  Not sure why your gauge is in Kpa, my guess is it also shows inches of wc on one of the scales.

Prior experience running and firing a gas kiln, operating pressure and damper throughout the segments would really help here. Set it and forget it while it can be done cycling on and off really limits learning rates, segments, reduction, etc….. speed and damper action experience can help a bunch in terms of firing more evenly.

Edited June 30, 2022 by Bill Kielb

[Mudfish]

yes, the gage does indicate inches. I have just now noticed that. So I actually fired in at 3", which was low. I thought I was at 3 kPa's , so this was my error.  I do have experience firing gas kilns, but not very consistently successful. it seems I usually have problems evening out temps. I used to fire a electric converted to natural gas, and my results were not consistent. So that is my experience. The previous owner had venturi burners set to natural gas, which is what I am firing on.  Gas lines are 1 and 1/4".  Here is my firing schedule as it reads on my controller: Six segments. Seg. #1 - 150f - 180f no hold.  Seg #2 - 150f -250f no hold. Seg #3 - 400f - 2030f no hold.  Seg #4 120f - 2280  with a 30 minute hold.  Seg #5 9999 (drop) to 2050 and a 30 minute hold. Seg #6 - 150f - 1500f no hold.    So, I did fire it like a "set it and forget it", but I mistakenly set gas valves to read at 3" on the gage. I thought this was 3 kPa, and I looked up a conversion, and thought I was firing at 7" wc. So now I know this was a mistake and was too low water column.  I did adjust the damper to get a reduction, but wares did not get much even though I did see flame from the spy holes. Maybe this was due to wc being too low.  Also, should I set gas valves to read at 7" wc and maintain that throughout the entire firing, or do I set valves to build up to 7" wc ?

Edited June 30, 2022 by Mudfish

[Bill Kielb]

Firing a gas kiln manually is really helpful as it’s about going certain speeds at certain times while managing your damper for the type of firing is an experience thing. Not hard, but having done it a bunch makes it become easy. Set it and forget it kind of doesn’t really exist with that kiln as if you read the instructions, they say you still need to manage your gas and of course damper. So setting it at max power 7” and running it from the start would not be the greatest. With respect to reduction, not hard as well but the more good experience the better. I think the manual I read gives folks little chance.

here is a video (not great) but it will give you a sense of schedule, firing speed and some insight into reduction that may spark some new questions / thoughts: https://youtu.be/Hzrsbf3NZLo

 

[neilestrick]

So the digital controller is cycling the gas on and off in order to achieve the rate of climb you program? Unfortunately, that won't work. Gas kilns need to have the burners on the entire time in order to maintain pressure inside the kiln, which is what will make it fire more evenly. A digital controller will only work if it's working in conjunction with a gas valve that is adjusted by the controller, and an automatic damper, too.

There are 3 adjustments that have to be made when firing a gas kiln: gas, air, and damper. With Venturi burners you can usually get the air set to where it doesn't need to be adjusted, but power blowers do need adjustment as you go along. So you have to set the gas and damper to achieve the rate of climb and level of reduction you want at any point in the firing. Generally the gas is slowly increased as the firing progresses, and the damper is adjusted accordingly. You can't just set it and leave it. I recommend trying a firing where you set the rate of climb on the controller to 9999, with a set point of your peak temp, and then fire the kiln manually, making the proper adjustments to gas, air, and damper.

[Mudfish]

yes, it is on/of controller. I am going to call Bartlett Control Systems and see if they can walk me through an override or something so that I can manually fire and just use the controller as a temp reader

[Mark C.]

Manually firing is the way to go. Burners should never cycle off or up and down. Thats a given . I doubt that kiln ever needs 7inchs (full on) start low and turn up a bit after quartz enversion (1100) then up some more around 1800 thats where I start light reduction . and around 2,000 maybe gas is at 3/4 on or 5-6 on guage.

You will need to see cones try for two cones if hole is small say a 7 and a 8 if you are firing for 8. Use a small soft brick or clay piece thats solid so cone stand out against that visually.

I have zero gas experience with a controller . I think Neils idea of 999999 so its out of the picture is a good one

in the kiln specs its says high limit controller  and thats what I think it should do limit the top end for safety. set that above cone 8 and fire with cones and eyeball 

[neilestrick]

26 minutes ago, Mudfish said:

yes, it is on/of controller. I am going to call Bartlett Control Systems and see if they can walk me through an override or something so that I can manually fire and just use the controller as a temp reader

Like I said, do a program with one ramp, rate of 9999, to your peak temp. It'll open the gas valve and leave it open until it reaches the temp. It'll read current temp as you fire, and act as a safety shutoff.

[Bill Kielb]

1 hour ago, Mudfish said:

yes, it is on/of controller. I am going to call Bartlett Control Systems and see if they can walk me through an override or something so that I can manually fire and just use the controller as a temp reader

You can use it as a high limit - see the instructions. Also posted a typical reduction schedule below to give you an idea of gas pressure gradual increase. Again it may clarify (a little bit) some things for you.

 

 

Edited June 30, 2022 by Bill Kielb

[Mudfish]

Just unloaded kiln from doing a single segment 9999 program. Went a little hotter than cone 8, just wanted to see what my base glazes looked like at a higher cone. Thought I could manually do a slow cool after a soak at 2320f.., but controller would just shut off burners, so next time I will do same program but add a slow cool segment also. Some bubbling over my base glaze, due to cooling off too quickly, but I'm just going to smooth them with sandpaper and call it good.  Kiln fired evenly also. Thanks all for the helpful responses. 

Edited July 3, 2022 by Mudfish

[Bill Kielb]

@Mudfish

2320 is more like cone 10, especially with a hold. If you have the three key Bartlett it can be set at a maximum 2350f for a high limit.

I would highly suggest you record your firing schedule to include gas pressure, damper position, time of adjustment, how fast your temperature has risen since last measurement. For the most part folks monitor and adjust approximately every 15-30 minutes. End the firing by observing witness cones (using proper protective glasses) not by temperature.

Recording all that stuff will start to give you a feel for how firings progress and you will be able to repeat results more easily IMO.

How long did this firing take, and it likely made near cone ten but hard to know exactly without witness cones.

since these wares are intended for food consumption you may want to consider, is your clay fully vitrified, are the glazes food safe and are they durable. Generally pinholes / blisters are a no go defect for many potters when the ware can hold food.

Edited July 4, 2022 by Bill Kielb