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Linda A

Gas kiln stalled . Why?

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Hello

I have a 9 cubic foot downdraft propane fired gas kiln.

I have an 11 foot chimney . I have 2  60,000 BTU Venturi burners.

I had a kiln controller but solenoids are disabled so am firing manually and just using the controller for watching the temp increase or decrease.

I have a 100 pound propane tank that was over three quarters full.  It has a pressure regulator which is set for 4  when tank is turned on.  There is also a further flat regulator between the valve to turn the propane on and before the piping branches out to each burner. Not sure what or why that is there.

I started firing at around 11:30 am with a preheated kiln  460 F.    This preheated temp was from an earlier aborted firing.

At 1220 temp was 787 F.     Temp rise 327 F   Gas open one quarter turn

2:20 pm.    981F.      Temp rise. 194 F   Gas full open

3:20.     1047F.    Temp rise. 66 F  adjusted air on burner a bit

4:30 pm.  1080 F. Temp rise 33F           gas closed  a quarter.

5:30 pm  1440 F  Temp rise 360F   Damper in half way

6:30 pm  1682   Temp rise   242    Gas increased by one quarter turn   Damper  3 inches open.

7:30  1806  temp rise 124    Damper  1.5 inches open   Gas open fully

8:30 pm   1890    Temp rise 84   Reduction started at 1824F for one half hour  Damper fully in but after 10 minutes pulled back slightly as too much smoke.

9:30 pm. 1967 F   Temp rise 77

10:30  1984 F  Temp rise 17        I was adjusting damper and gas slightly throughout this time from 9:30 to 12:30  . Sometimes adjustments would make temp decrease or slight increases .

11:30  2031  Temp rise 50F

12:30  2041F     Temp rise 10F

12:30-1:30 am  2050   Then stalled

Does anyone have any ideas on why I could not reach  cone 6.  I shut off kiln because at 10 degree increments per hour I would probably still be sitting ther looking at flames.

Is there a problem with my burners?   They are quiet, are they supposed to be noisy  with a more intense flame   My flame is blue green at the base with orange on tips. It is about 12-14 inches high and quiet  . My pilot light is noisier than burners

Or is it the pressure valve on the tank.

I just don't know. Any ideas.

Thankyou

 

 

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Lots of possibilities, all of which are very difficult to diagnose without being at the kiln to make adjustments to see how it responds. My first gut feeling is that maybe you are using too much gas.

Where are the air inlet dampers set on the burners? 1/4 inch open? Less? More?

At no time should you ever have the damper closed all the way. You are not trying to trap heat in. You are moving heat through the kiln. Hot air comes in, transfers heat to the ware, moves out and is replaced by more hot air. It is breathing. Electric kilns trap radiant heat, gas kilns move hot air through.

How much back pressure did you have? Flame out both top and bottom spy holes?

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Would have thought you'd be hearing those burners go.

Are the air inlets on burners open?

As Neil said hard to judge.

All of what Neil said really.

Try Air nlets on burners fully open till try to reduce.

Damper adjusted but don't close till turn off kiln

Not being Fahrenheit  I can' see at a glance the temp rise per hour.

The valve close  to your burners is where you turn on gas to burners after pilot light is lit. Some folk may candle over night with pilot lite

That's where I'd be adjusting gas flow to kiln .a meter there would allow the psi to kiln to be measured accurately.

Edited by Babs

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Reduction close airinlet on burners and adjust damper.

If reducing the flaw will lick out the bung holes searching for oxygen.

Keep at it!

Success first time  boring!!!

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2 hours ago, neilestrick said:

Lots of possibilities, all of which are very difficult to diagnose without being at the kiln to make adjustments to see how it responds. My first gut feeling is that maybe you are using too much gas.

Where are the air inlet dampers set on the burners? 1/4 inch open? Less? More?

At no time should you ever have the damper closed all the way. You are not trying to trap heat in. You are moving heat through the kiln. Hot air comes in, transfers heat to the ware, moves out and is replaced by more hot air. It is breathing. Electric kilns trap radiant heat, gas kilns move hot air through.

How much back pressure did you have? Flame out both top and bottom spy holes?

The air inlet valves were only open about one eight of an inch.  Any further open than that they would become very loud.  Is that normal?

At one point early mid firing I had flame out of one spy hole.  I don't have 2.  But if I put a lit candle up to the hole it would blow out instantly

during most of the firing.

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56 minutes ago, Babs said:

Would have thought you'd be hearing those burners go.

Are the air inlets on burners open?

As Neil said hard to judge.

All of what Neil said really.

Try Air nlets on burners fully open till try to reduce.

Damper adjusted but don't close till turn off kiln

Not being Fahrenheit  I can' see at a glance the temp rise per hour.

The valve close  to your burners is where you turn on gas to burners after pilot light is lit. Some folk may candle over night with pilot lite

That's where I'd be adjusting gas flow to kiln .a meter there would allow the psi to kiln to be measured accurately.

Hi Babbs

Am I supposed to be hearing a sort of roaring sound. As I told Neil I have the air discs closed to about 1/8 of an inch. I do get a roaring sound if opened up, BUT how much do I open up.

 I was adjusting the gas just down from the tank before the flat regulator and before it branches out to two burners.  If I adjust at the burners I would have to adjust each one separately .  Is that ok

My instructions that came with the kiln state that the airdiscs on the bottom of the burners should be nearly closed otherwise I will get burn back in the burners and damage them.   Is this correct

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55 minutes ago, Babs said:

Reduction close airinlet on burners and adjust damper.

If reducing the flaw will lick out the bung holes searching for oxygen.

Keep at it!

Success first time  boring!!!

I WANT success the first time.

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You should not have to adjust the air inlets on the burners durning the firing once you get them set correctly. You should be able to adjust reduction using the gas and damper only. For now, get as much air as you can without them roaring too much. Adjust the gas until the temp rises at the desired rate. Adjust the damper until you have back pressure out both spies. You'll have a lot out of one, a touch out of the other. It'll take going back and forth with the gas and damper until everything is working in sync. It is possible to use too much gas, so go easy at first, like just open a little bit. You should be gradually increasing the gas, and probably opening the damper as the temp climbs. Up till about 1600 degrees you can do just about anything and it'll get hotter, but start working on dialing things in starting at about 1000.

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Ok I have more air and not too much roaring. Gas is adjusted for rate of climb and I have air blowing out of one spyhole.  Can see by candle flame so I have back pressure.   

To get back pressure I have to put damper in part way.  Is that correct?  Gas is just open a bit..

i will gradually increase the gas to 1000 degrees.  I assume you are talking Fahrenheit.

then what do you mean dialing  things in.   Do I start reducing at 1800.

Thankyou

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By start dialing things in at 1000 I mean get things in sync with your adjustments. Prior to that it doesn't really matter. Reduction at 1800 is fine. You need back pressure out both the top and bottom spy holes for it to fire evenly.

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So far I'm in 100% agreement on fixes.My guess is also the burners are starved for air(open the inlets)and to much gas added.

Never close the damper all the way except when done firing.

My air inlets are almost always set on full open and I just ass more gas . I have not adjusted them in decades once they are set right. The burners will roar later in firing.-noise is ok.

Just loaded two glaze fires myself and am firing in am.

 

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35 minutes ago, neilestrick said:

By start dialing things in at 1000 I mean get things in sync with your adjustments. Prior to that it doesn't really matter. Reduction at 1800 is fine. You need back pressure out both the top and bottom spy holes for it to fire evenly.

Ok thanks

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12 minutes ago, Mark C. said:

So far I'm in 100% agreement on fixes.My guess is also the burners are starved for air(open the inlets)and to much gas added.

Never close the damper all the way except when done firing.

My air inlets are almost always set on full open and I just ass more gas . I have not adjusted them in decades once they are set right. The burners will roar later in firing.-noise is ok.

Just loaded two glaze fires myself and am firing in am.

 

 

13 minutes ago, Mark C. said:

So far I'm in 100% agreement on fixes.My guess is also the burners are starved for air(open the inlets)and to much gas added.

Never close the damper all the way except when done firing.

My air inlets are almost always set on full open and I just ass more gas . I have not adjusted them in decades once they are set right. The burners will roar later in firing.-noise is ok.

Just loaded two glaze fires myself and am firing in am.

 

THANKYOU.    Good luck with your firing

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I guess kilns are different.

I did adjust the primary air flow at burners on starting to reduce..

Memorizing here, I may even backed off with the gas at that point too.

No need to adjust gas at each burner though some start the firing with only one burner on for slow s tart to the day or, overnight.

All the best

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I suggest just turn in the gas on low and have your air dampers on burners open as you want more heat after 800 degree just slowly turn up the gas on both burners-after the kiln is 1000 degrees you can go faster.I leave the damper open until reduction at 1800 then put it in some to get mild reductions(no smoke).The reduction usually lightens as it climbs in temps but after say 2100 it remains stable.Since you are going to cone 6 this may be a bit different but after say 2100 I can adjust the  damper and leave it alone until kiln turned is off. Making 10,00 adjustment will only add to the confusion . Try to adjust only one thing at a time and see the results. Then if not happy try the other thing. Not both at once.

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Usually when a kiln stalls at the top of the schedule, it's not always obvious that it needs adjustment. You might just stare and say "Huh?" ;)

I agree with the others on needing more air and/or more draw through the flue.

The schedule looks good, but yes, by 1000 degrees you can advance easily 100-200 degrees an hour by adjusting both your gas and air.

The flame needs to be burning all the fuel with as much air as required to bring the flame to max heat.

Adjusting the flue is key as well. You don't want all your heat going up the chimney, but just enough to keep the temp on course.

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I agree with theneed for air on the burners. 

Question: what altitude are you? If you are at a high altitude, is your chimney giving you sufficient draft. when the kiln is empty, light a piece of news paper , put it near the flue and see if the flame is drawn into the flue.

When reducing you should have a hard flame( bluish) coming out the top peep and a licking flame on the bottom.

Marcia

 

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18 hours ago, Babs said:

I guess kilns are different.

I did adjust the primary air flow at burners on starting to reduce..

Memorizing here, I may even backed off with the gas at that point too.

No need to adjust gas at each burner though some start the firing with only one burner on for slow s tart to the day or, overnight.

All the best

Ok Thanks

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7 hours ago, Rex Johnson said:

Usually when a kiln stalls at the top of the schedule, it's not always obvious that it needs adjustment. You might just stare and say "Huh?" ;)

I agree with the others on needing more air and/or more draw through the flue.

The schedule looks good, but yes, by 1000 degrees you can advance easily 100-200 degrees an hour by adjusting both your gas and air.

The flame needs to be burning all the fuel with as much air as required to bring the flame to max heat.

Adjusting the flue is key as well. You don't want all your heat going up the chimney, but just enough to keep the temp on course.

THANKYOU.  Yes I think my burners were not adjusted correctly.  I had the disc at the bottom closed almost tight so will open it next time and see what happens. And be a little more careful with the damper controls.  I was thinking it was like a wood stove, close the damper and more heat into the house but with Neil's explanation I was totally wrong.    Hopefully I will get this figured out.  It's to hot here to fire now, will have to wait for cooler weather.

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18 hours ago, Mark C. said:

I suggest just turn in the gas on low and have your air dampers on burners open as you want more heat after 800 degree just slowly turn up the gas on both burners-after the kiln is 1000 degrees you can go faster.I leave the damper open until reduction at 1800 then put it in some to get mild reductions(no smoke).The reduction usually lightens as it climbs in temps but after say 2100 it remains stable.Since you are going to cone 6 this may be a bit different but after say 2100 I can adjust the  damper and leave it alone until kiln turned is off. Making 10,00 adjustment will only add to the confusion . Try to adjust only one thing at a time and see the results. Then if not happy try the other thing. Not both at once.

Ok, I will try your suggestions when I attempt to fire again.   Thanks

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5 hours ago, Marcia Selsor said:

I agree with theneed for air on the burners. 

Question: what altitude are you? If you are at a high altitude, is your chimney giving you sufficient draft. when the kiln is empty, light a piece of news paper , put it near the flue and see if the flame is drawn into the flue.

When reducing you should have a hard flame( bluish) coming out the top peep and a licking flame on the bottom.

Marcia

 

I live on Vancouver island. I will try your lighting  peice of paper idea.  Thanks

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On 7/23/2018 at 6:28 PM, Linda A said:

I have a 100 pound propane tank that was over three quarters full.  It has a pressure regulator which is set for 4  when tank is turned on.  There is also a further flat regulator between the valve to turn the propane on and before the piping branches out to each burner. Not sure what or why that is there.

I am still not convinced that regulator is for propane pressure instead of natural gas. I think you need to find out what pressure that regulator is outputting. Whatever it is saying on the gauge wont matter once you hit the constant pressure the flat regulator is outputting.  

 

I may be completely wrong as nobody else seems to be worried and it's not a constant pressure regulator.

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36 minutes ago, High Bridge Pottery said:

I am still not convinced that regulator is for propane pressure instead of natural gas. I think you need to find out what pressure that regulator is outputting. Whatever it is saying on the gauge wont matter once you hit the constant pressure the flat regulator is outputting.  

 

I may be completely wrong as nobody else seems to be worried and it's not a constant pressure regulator.

From my readings it seems like that flat regulator is a second stage regulator and the one at the tank is a first stage regulator.  

On the flat regulator , the one down from the tank, it says inlet pressure 10 psi.  Don't know what outlet pressure is but assume 11 inches of water column as that seems to be the standard. At least for household, don't know if a kiln would be different.  My burners are 60,000 BTU's.

Also from my readings both regulators are needed.  It seems most regulators have first and second stage in one but I seem to have a different setup.

When I was firing my kiln I was using the valve between the first and second regulator to control gas to the burners but I am thinking I should be controlling the gas with the valve that is situated at each  burner after the flat regulator.  What do you think.

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Yes you should use the valves closest to burners to regulate them for sure. That should all be downstream of any regulator.

As to natural gas was the kiln bought from an are that had Natural gas?? of all propane area??

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