Kiln still stalling

[Linda A]

Hello all

i am firing my 9 cubic foot downdraft gas kiln.

I reached 1966 degrees F.   My gas pressure at that time was fully open at 12 .Then kiln stalled.  Previously I was told that when my kiln stalls I need to lower the gas.  I turned the  gas pressure down to 9.  Kiln temp has been dropping steadily.  I am now at 1773.  What am I doing wrong.

 My damper is closed to one quarter inch open.

thankyou.  Linda

[Mark C.]

open the damper a bit and let the kiln breathe

[liambesaw]

Yep, gotta get air through it.  Just put a 5.5 foot chimney on mine tonight and man she can rip now that she gets more air through her.  Only had a 2 foot chimney before and it struggled to keep up.

[Mark C.]

Gas kilns need air and gas going in and out.

The damper controls the reduction. There is sweet spot where its reducing and also climbing -then with a little to much damper in it will stall. Same is true buy giving it to much gas. To much gas can also stall it as it does not get enough air to combust.

Its either one or the other or both that can make for a stall. 

My kiln when adjusted right climbs slowly but it does climb.You failed to mention what cone you are hoping to get to? but I'm assuming 5 or 6??

I'm going to sleep now but have given you the two control factors- am assuming you have a good chimney to make for a draw or are using forced air as you did not say ?

The last thing is if its propane make sure its not freezing at the tank and if it is trickle some water over tank and valve.

good luck and let me/us know how this works out

 

[liambesaw]

Your kiln needs to move hot air through it, that's how it heats, so when you close the damper and turn up the gas, there's only a little bit of air coming through the kiln.  Once you make a nice pathway for the air to flow through you can adjust the gas up or down.  But there needs to be air, the gas won't do it by itself.  

[Mark C.]

This is where I hope you have digital pyrometer to see small changes in temps

[Linda A]

Thanks for your input.

i tried opening damper a bit.  Temp continued to decrease. I eventually stopped firing after I had decreased two hundred degrees with no hope of turning around and increasing.  I had a nice blue flame throughout.

It did not seem to matter what I did, increase, decrease gas, open , close damper.

I had looked at the formula for chimney height and had that correct.  Fired a couple of days ago.  No go again.

Took four feet off chimney same situation as before. Kiln stalled after 1900.

Is there such a thing as too much draft.  I was thinking of firing with only the three foot chimney that the kiln came with.

From the beginning of the three firings that I have attempted , after about 500 degrees I have to start using the damper to get any heat rise. By the time I am close to 1900 the damper is in almost to the reducing line again which I obviously don't want.

The gas also has to be on 12 " WC.   Kiln also starts to slow at 800 and 1400 degrees but with persuasion I am able to keep rising.  Mainly with damper in adjustments. Tried fiddling with the gas at those points and kiln started to decrease.

I had one hundred pounds of propane each firing, the last two did have some frost on the lower two feet of the tank.

Any ideas.

Thanks   Linda

 

[PatIsGone]

Do you have a pressure gauge on your line between the tanks and the burner? I'll bet your tanks are freezing up and the pressure is dropping ( = less fuel = decreasing temps).  If you have multiple tanks daisy-chained together, don't run them all at the same time.  As one starts to freeze up, turn it off and the other on.  I've babied firings this way, shutting one off and the other on as they freeze and thaw.  If you only have one tank, a second one would be a possible fix.

If it is a air flow problem, take a air hose (hair dryer?)  and shoot fresh air in next to burner.  You should see temp increase.  If you don't, you're burning all the fuel you put in, and you need more fuel - thus, your pressure may be dropping when the propane is too cold to boil (vaporize) in the volume you need it to.  Make sense?

[Rex Johnson]

What sort of burner arrangement do you have?

Venturi or forced air?

Bottom or side burners and how many?

Propane or natural gas?

My propane kiln is about the same size with two forced air burners and a downdraft.

Yesterday for the first time (only glaze firing this year) it stalled at about 2100 on a cone 6 firing.

It took a lot of coaxing to get it to temp, flue and air flap adjustment, but gas full on.

In the end once it got to ^ 6+,  I started turning it down for a level  soak, gas about at 1/2, air flaps about 1/2 normal.

(Again) to my surprise, the temp actually went UP!

So yeah, the right mixture and flow is important.

[liambesaw]

2 hours ago, Rex Johnson said:

What sort of burner arrangement do you have?

Venturi or forced air?

Bottom or side burners and how many?

Propane or natural gas?

My propane kiln is about the same size with two forced air burners and a downdraft.

Yesterday for the first time (only glaze firing this year) it stalled at about 2100 on a cone 6 firing.

It took a lot of coaxing to get it to temp, flue and air flap adjustment, but gas full on.

In the end once it got to ^ 6+,  I started turning it down for a level  soak, gas about at 1/2, air flaps about 1/2 normal.

(Again) to my surprise, the temp actually went UP!

So yeah, the right mixture and flow is important.

Haha isn't that great, can't count the number of times I struggle on the last 100 degrees only to give up and cut the gas down for a slow cool only to have the dang thing start climbing again.  Oh, and the prerequisite is that it only works when you don't need it to.  Isn't gas firing fun?! 

Haha all joking aside, I wouldn't trade it for anything. It's a lot of fun and plenty of beer gets drank on firing days.

[neilestrick]

Can you post a picture of your kiln and burners?

[Linda A]

7 hours ago, Patrick said:

Do you have a pressure gauge on your line between the tanks and the burner? I'll bet your tanks are freezing up and the pressure is dropping ( = less fuel = decreasing temps).  If you have multiple tanks daisy-chained together, don't run them all at the same time.  As one starts to freeze up, turn it off and the other on.  I've babied firings this way, shutting one off and the other on as they freeze and thaw.  If you only have one tank, a second one would be a possible fix.

If it is a air flow problem, take a air hose (hair dryer?)  and shoot fresh air in next to burner.  You should see temp increase.  If you don't, you're burning all the fuel you put in, and you need more fuel - thus, your pressure may be dropping when the propane is too cold to boil (vaporize) in the volume you need it to.  Make sense?

Yes I have pressure gauges.  I have one at the tank. That gauge always reads 5. Then a secondary one down the line to change the pressure  going to the burners to 12 inches WC .  I just put on another water column pressure gauge with a valve so I can  adjust the gas by inches of water column. Open full is 12 inches, almost closed is 4 inches.

i will try the hair dryer trick.

Thanks

[Linda A]

4 hours ago, Rex Johnson said:

What sort of burner arrangement do you have?

Venturi or forced air?

Bottom or side burners and how many?

Propane or natural gas?

My propane kiln is about the same size with two forced air burners and a downdraft.

Yesterday for the first time (only glaze firing this year) it stalled at about 2100 on a cone 6 firing.

It took a lot of coaxing to get it to temp, flue and air flap adjustment, but gas full on.

In the end once it got to ^ 6+,  I started turning it down for a level  soak, gas about at 1/2, air flaps about 1/2 normal.

(Again) to my surprise, the temp actually went UP!

So yeah, the right mixture and flow is important.

So I have 2 Venturi burners pointing vertical up against the back wall of the kiln.

I use a 100 lb propane tank which was full.

The air flap really only has one adjustment otherwise I have burnback.  That adjustment is only slightly open.

The only way I can get any temp rise is with gas on full and increasingly closing up damper.  Is that normal?

It just seems like I have a ton of heat loss billowing out of the chimney.   Way too much draft.

This kiln is very easy to put in reduction but I only want to do that for 45 minutes.

I was thinking of decreasing the chimney height to just three feet.

What do you think.

linda

[liambesaw]

6 minutes ago, Linda A said:

Yes I have pressure gauges.  I have one at the tank. That gauge always reads 5. Then a secondary one down the line to change the pressure  going to the burners to 12 inches WC .  I just put on another water column pressure gauge with a valve so I can  adjust the gas by inches of water column. Open full is 12 inches, almost closed is 4 inches.

i will try the hair dryer trick.

Thanks

From reading up a little you said the bottom of the tank was frozen, I think you found your issue.  Tanks freeze pretty quick with the valve all the way open, and once it happens you either switch tanks or the amount of gas will steadily decline.  Once there's frost on the tank it's only a matter of time.

[liambesaw]

4 minutes ago, Linda A said:

So I have 2 Venturi burners pointing vertical up against the back wall of the kiln.

I use a 100 lb propane tank which was full.

The air flap really only has one adjustment otherwise I have burnback.  That adjustment is only slightly open.

The only way I can get any temp rise is with gas on full and increasingly closing up damper.  Is that normal?

It just seems like I have a ton of heat loss billowing out of the chimney.   Way too much draft.

This kiln is very easy to put in reduction but I only want to do that for 45 minutes.

I was thinking of decreasing the chimney height to just three feet.

What do you think.

linda

For natural draft kilns there should be 3 feet of chimney to every foot of downward pull, plus 1 foot of chimney to every 3 feet of horizontal pull.

 

That is from a free handout on kiln design.

https://ceramicartsnetwork.org/wp-content/uploads/2010/05/gaskilnsfreemium.pdf 

For my 8 cuft kiln that's 5.5 feet tall.

[Linda A]

2 hours ago, liambesaw said:

Haha isn't that great, can't count the number of times I struggle on the last 100 degrees only to give up and cut the gas down for a slow cool only to have the dang thing start climbing again.  Oh, and the prerequisite is that it only works when you don't need it to.  Isn't gas firing fun?! 

Haha all joking aside, I wouldn't trade it for anything. It's a lot of fun and plenty of beer gets drank on firing days.

Happy that yours worked out. When I turned my gas down the kiln went down 200 degrees. Very frustrating!!  At that point had been firing for 15 hours so I gave up.

[neilestrick]

I'm also wondering if you're using a large enough hose. If it's too small, then you're not getting the volume of gas you need, even if you're getting the correct pressure. Did your kiln come with the hoses and regulators you're using? Are you sure the burners are set up for use with propane? What brand kiln is it?

[Linda A]

17 minutes ago, liambesaw said:

From reading up a little you said the bottom of the tank was frozen, I think you found your issue.  Tanks freeze pretty quick with the valve all the way open, and once it happens you either switch tanks or the amount of gas will steadily decline.  Once there's frost on the tank it's only a matter of time.

 But why was the pressure reading still at 12 inches on the gauge when gas fully on.

[Linda A]

9 minutes ago, neilestrick said:

I'm also wondering if you're using a large enough hose. If it's too small, then you're not getting the volume of gas you need, even if you're getting the correct pressure. Did your kiln come with the hoses and regulators you're using? Are you sure the burners are set up for use with propane? What brand kiln is it?

Kiln came with the hoses and regulators. We just put the regulator on to measure inches of water column.

yes the burners are set up for propane.  We do not have gas here.   It is an estrin, no longer made.

Thanks

[liambesaw]

28 minutes ago, Linda A said:

 But why was the pressure reading still at 12 inches on the gauge when gas fully on.

Don't know, you also mention the valve at the tank is set to 5 inches and the burners set to 12, so I'm not sure how that works out.

[Linda A]

29 minutes ago, liambesaw said:

Don't know, you also mention the valve at the tank is set to 5 inches and the burners set to 12, so I'm not sure how that works out.

At the tank is a first stage regulator which is in psi. It decreases pressure from the tank to the line. This goes to a second stage regulator which changes the pressure from the line coming out of the tank to 12 inches of water column. The regulator we put on after the second stage regulator is just a dial with a ball valve so we can adjust gas pressure from the second regulator. This line goes to both burners.

i think most propane systems have a first and second stage regulator as one unit but mine is separate for some reason.

If I am wrong in my above deductions of regulators someone let me know.

Thankyou

 

[liambesaw]

40 minutes ago, Linda A said:

At the tank is a first stage regulator which is in psi. It decreases pressure from the tank to the line. This goes to a second stage regulator which changes the pressure from the line coming out of the tank to 12 inches of water column. The regulator we put on after the second stage regulator is just a dial with a ball valve so we can adjust gas pressure from the second regulator. This line goes to both burners.

i think most propane systems have a first and second stage regulator as one unit but mine is separate for some reason.

If I am wrong in my above deductions of regulators someone let me know.

Thankyou

 

Ahh ok, so 5psi down to 12 inches, makes more sense, what's 12 inches wc, like 1 psi or something? I don't measure my pressure, I go by ear.  

I hope you figure it out, if the chimney came with the kiln it's probably correct for the draft.  You can always take the measurements.  

The chimney opening should be 1/5th the size of the wall of the kiln at the minimum, 1/4th at the maximum, 3 feet for every foot of downward pull plus 1 foot for every 3 feet of horizontal pull.  My inner dimensions are 20 inches square, (20 inches/12 inches in a foot * 3 feet of chimney per downward pull = 5 feet of chimney) + (20 inches/12 inches in a foot / 3) is roughly 5.5 feet.

Pain in the butt, but worth doing to make sure your kiln is set up for a good draft.

I'm just following that design, which I've seen in library books on kiln building by i think Ian Gregory as well.

Dunno, I don't have to run my damper closed unless I'm on reduction and I use a single weed burner

 

[Linda A]

16 minutes ago, liambesaw said:

Ahh ok, so 5psi down to 12 inches, makes more sense, what's 12 inches wc, like 1 psi or something? I don't measure my pressure, I go by ear.  

I hope you figure it out, if the chimney came with the kiln it's probably correct for the draft.  You can always take the measurements.  

The chimney opening should be 1/5th the size of the wall of the kiln at the minimum, 1/4th at the maximum, 3 feet for every foot of downward pull plus 1 foot for every 3 feet of horizontal pull.  My inner dimensions are 20 inches square, (20 inches/12 inches in a foot * 3 feet of chimney per downward pull = 5 feet of chimney) + (20 inches/12 inches in a foot * (1 foot for every 3 feet of horizontal pull)) is roughly 5.5 feet.

Pain in the butt, but worth doing to make sure your kiln is set up for a good draft.

I'm just following that design, which I've seen in library books on kiln building by i think Ian Gregory as well.

Dunno, I don't have to run my damper closed unless I'm on reduction and I use a single weed burner

 

My problem seems to be too good of a draft. I can see heat billowing out of the chimney and the only way I seem to get heat rise up to cone 010  (this is when I reduce for 45 minutes) is by closing off the damper in increments .  By the time I am at cone 010 damper is pretty close to my reduction line.  Doesn't seem right.  This is with gas turned up full from beginning or gas increased slowly over a longer period of time.

How long does it take you to fire to cone 6.

[liambesaw]

5 minutes ago, Linda A said:

My problem seems to be too good of a draft. I can see heat billowing out of the chimney and the only way I seem to get heat rise up to cone 010  (this is when I reduce for 45 minutes) is by closing off the damper in increments .  By the time I am at cone 010 damper is pretty close to my reduction line.  Doesn't seem right.  This is with gas turned up full from beginning or gas increased slowly over a longer period of time.

How long does it take you to fire to cone 6.

Takes me 8 hours for a glaze firing to cone 6.  If it was too much of a draft wouldn't adjusting the damper down fix it?  I can get to about 1800 in my kiln without touching a thing and only having the burner on about a quarter to a half turn, the last 300 I juggle adjusting the burner and damper.  You have a 100 pound tank, I have a 40, and it takes me about 25 pounds for a glaze firing.  But my kiln is smaller.

[neilestrick]

Can you post some pictures, including the inside of the kiln, burners, burner ports, flue opening, etc.