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docweathers

Olympic 2728G Kiln stuck at 974°C

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docweathers    79

I just tried my first glaze firing in my used Olympic 2728G kiln. I got to 974°C and could go no further. The problem was obvious but the solution is not. The kiln was reducing strongly both as evidenced by 2 foot yellow flames coming out of the vent and my oximeter showing strong reduction. My manifold pressure was less than one IWC. When I would raise the manifold pressure the flames would get even taller and my pyrometer indicated it actually got cooler.

 

I'm using propane. When I assembled the kiln, I checked the gas jet size and it was according to factory specifications for propane. I also cleaned each of the jets. I have the air control valves on all 6 burners all the way open. It seems obvious that I need to get more air into my burners but it is less obvious how to do that given that the air valves are already all the way open.:(I

 

Suggestions please

 

Thanks Larry

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Mark C.    1,805

Tell me about where the damper setting was when it stalled out-was it choked off or all the way open was there more room to open it further??

Is that a 2 or 4 burner trash can kiln? sounds like plenty of fuel I'm thinking to much.

 

Mark

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Mark C.    1,805

OK

what are the chances you had it turned up to much?

I'm thinking to much fuel that reduces so much you loose temperature and cannot gain.Just a thought.

With a two foot flame with damper all the way open thats I have.

How about turning it down some and and controlling the reduction with the damper-thats my suggestion.

mark

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docweathers    79

Mark

 

Thanks for your suggestion. I carefully adjusted the manifold pressure up and down to even get to 974°C. I was only able to get to that temperature by keeping the manifold pressure less than 1 inch of water, though I have 11 inches of water available.

 

thanks Larry

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Mark C.    1,805

Doc Weathers

I have some experience with propane but more with 1/4 # or 7 inches of water with natural gas.

My thought is if you have two feet of flame and the oxy probe #s are high and damp is wide open then either the load is such that its impeding the flow or the fuel is to much hence the reduction. When I have say a bag wall collapse or I stack the flue to dense then the kiln no mater what I do reduces to much. The only other point is- I have put to much gas into the kiln for it to climb and the by product is reduction to the moon. This is a small kiln ( I looked it up) and will not need much to get it to climb.

You can always call Torchbearer and talk about pressures.

Hope this helps

Mark

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Mark C.    1,805

That link said

(Original pipe burners replaced with MR-750 Venturi burners.)

I have 4 of these on my salt kiln and they rock.

Mark

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docweathers    79

Thanks for all of the useful advice. As per JD3's post, I am pursuing getting a second pyrometer.

 

What is the difference/advantage of the MR-750 Venturi burners over the original burners. I have one of the early versions of the Olympic 2728G Kiln which has six burners versus the current model which I think has four. Axner sells these burners for $43.50. With shipping I will be into this almost $300:huh:. I only paid $500 for the kiln, hood and furniture. I wonder at what point I start over with another kiln.

 

I think my core problem is that my current burners are unable to mix enough air with the propane. Is there any way to get them to mix even more air or is there something that happens to them over time that restricts their original ability to mix air. (The air valve is wide open on all 6 of them)

 

I have contacted great kilns, the manufacturer, and sent them detailed descriptions and pictures. Hopefully they will have some brilliant insights into how to fix this thing cheap.

 

Does anyone know if this is a regular problem with this kind of kiln? Or, is this unique to my particular kiln?

 

Thanks Larry

 

 

 

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neilestrick    1,381

If you had 2 foot flames coming out the top, you were reducing too hard. Back off on the fuel. Call Olympic to get a recommendation on settings.

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docweathers    79

You are right I was reducing too hard at some points.

 

I have been corresponding with Olympic. They recommended 8 inches of water maximum pressure. If I even got to 1 inch, the reduction flames were huge. I sat for a long time fiddling with the gas pressure valve and watching the pyrometer. At something under 1 inch ( my manifold pressure gauge does not read well under 1) I was able to get to a maximum temperature of 974°C. If I increased the manifold pressure, the temperature actually started going down because the increased reduction.:(

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neilestrick    1,381

8 IWC is just barely over 1/2 pound. I'm thinking maybe your gauge is reading pounds, but you need to be firing IWC. If so, you need a different gauge.

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docweathers    79

my gauge reads in both IWC and pounds. in my initial post in this topic, I misstated pounds and what I should have said was IWC. since initial post I got my act together and have correctly stated everything in IWC.

 

I took my burners out and disassemble them. the piece of pipe screwed in the top of each one of them had a significant flange on the inside, both top and bottom, from the pipe cutter that was originally used to make them.... 30+ years ago. This would appear to restrict airflow significantly.

 

I took a reamer and cut this out of each of them and have reinstalled the burners. I am running a test right now, bringing the kiln, with some junk pots in it, up to temperature fairly quickly to see if this solved the problem. I am only at 400°C so far but things are looking better.

 

thanks for your input

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oldlady    1,323

would Ward Burner Co help? i think his name is Mark, too. this guy is awesome.

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Mark C.    1,805

One thought I have is that the orifice is to big for these burners-I realize you said it is a propane size but it sounds like smaller one would work better-less gas more air and a better mix overall. This test is cheap and easy to do. Get 6 small orifices and progressively drill them out till they purr. I would change these out before considering new burners- Have 6 burners on this small kiln means it should heat even and fast-maybe to fast. All I can think is to much gas -so choke it down at the orifice.

If you do repower in the future maybe 4 burners would do you.

Mark

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docweathers    79

One thought I have is that the orifice is to big for these burners-I realize you said it is a propane size but it sounds like smaller one would work better-less gas more air and a better mix overall. This test is cheap and easy to do. Get 6 small orifices and progressively drill them out till they purr. I would change these out before considering new burners- Have 6 burners on this small kiln means it should heat even and fast-maybe to fast. All I can think is to much gas -so choke it down at the orifice.

If you do repower in the future maybe 4 burners would do you.

Mark

 

 

That's a good idea? How would a smaller orifice be different than just keeping the manifold pressure lower? At this point, about 1/2 inch of water seems to be optimal for this contraption.

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Mark C.    1,805

Orifice size is key to have the right mix of air and gas pressure to make the venturi work properly-turning down the gas with to large a orifice is not the same as having the right size. Marc Ward will elaborate on this when called -he knows this stuff inside and outside-good call.

mark

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docweathers    79

I talked to Ward today. He suggested reducing the orifice size from the factory recommended 5/64 to 1/16 inch. I have done this. When I tested it, I can run more manifold pressure, like 7 inches of water. However, it still begins to reduce strongly about 800°C as evidenced by yellow flames out the vent and my oximeter. It may be a little less reduction, but not much.

 

This thing presents quite a puzzle for such a simple machine.

 

What do you suggest?

 

Thanks Larry

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docweathers    79

For however helpful in might be to someone else, I want to report back in on what appears to be the final solution to my burner problem. Jon Pacini of Laguna technical support suggested that I continue to reduce the orifice size down to a number 58 drill, which is a little smaller than 3/64ths. . Though I haven't done a full firing yet, with the lid open and at 7 inches of water pressure the flames are now about 10 inches high above the floor of the kiln. The top 1/5 th is yellow and the bottom 4/5 is blue. This seems about right to me.

 

I want to thank all of the people on this forum, as well as Mark Ward and Jon Pacini, who offered much good advice. The least helpful people were Olympic Kilns Co. In fact, they were the real source of my difficulty given that the repeatedly asserted that 5/64 jet size was appropriate for propane on my kiln .

 

Thanks to all

 

Larry

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