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Linda A

Kiln still stalling

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39 minutes ago, liambesaw said:

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.

 

39 minutes ago, liambesaw said:

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.

Yes it does help but I run out of damper adjustments by 1900 degrees. Kiln will be in reduction.  My kiln reduces only when damper is in with less than a quarter inch of the chimney open.  I then get a nice 4 inch flame out of the top peep.

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33 minutes ago, neilestrick said:

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

Hi Neil

Yes.  I will post some pictures tommorow afternoon.

Thanks.  Linda

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I do recall your kiln from the photos back awhile ago.I do not think its to much draft. My guess is the gas is freezing or supply line is not right from tank to kiln.

You have long venturi burned I remember-just make sure the air flaps are open.

Glaze fires take -8-12 hours for cone 10 . 8 hours seems about right for cone 6

Forget about the top peep-only check the bottom peep

I would not take the chimney down. 

Could you give the cubic foot size of kin again? and what size is the flue exit?

where is the damper in the chimney?

If I recall this kiln has no chimney ?

 

 

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9 minutes ago, Mark C. said:

I do recall your kiln from the photos back awhile ago.I do not think its to much draft. My guess is the gas is freezing or supply line is not right from tank to kiln.

You have long venturi burned I remember-just make sure the air flaps are open.

Glaze fires take -8-12 hours for cone 10 . 8 hours seems about right for cone 6

Forget about the top peep-only check the bottom peep

I would not take the chimney down. 

Could you give the cubic foot size of kin again? and what size is the flue exit?

where is the damper in the chimney?

If I recall this kiln has no chimney ?

 

 

Hello Mark

The air flaps are open a smidge. I had one of the old potters here come and look at them.  If they are open any more than a smidge I get burn back where the gas is igniting in the throats of the burner and the burner is loud.. I was told by the old potter that this was not correct , that the fire is supposed to ignite at the top of the burner and that Venturi burners are very quiet.

i would love to have a glaze firing to cone 6 only take 8 hours. I have tried firing this kiln 4 times.  The longest was 19 hours and I did not get to cone 6.  Only 2000 degrees.   Other firings slightly shorter but nothing over 2000 degrees.  The two previous firings this summer were not successful and I did not have propane tank with ice on the lower two feet as I have the last two firings this month.  It is colder now but not freezing.

And what am I checking in the bottom peep. I thought I was supposed to have a 4 inch flame out of the top peep and not much out of the bottom.  This is during reduction.

I did do the candle test at the bottom peep to check the atmosphere.  I was only able to have the candle flame go in side the hole at the early stages of firing. After 500 degrees the candle flame was blown out right away from the draft blowing out the bottom peep.

i am going to re measure it tommorow and will post pics of the flue, damper etc.

This kiln does have a chimney about three feet tall.  We addedon 8 feet of metal pipe for three firings.  This last firing we took off three feet but did not notice a difference.

Of note.  When I first got the kiln last year we were just doing a test fire with the three foot chimney.   We got up to 1400 degrees in no time with no damper usage but then the solenoids started acting up so it was shut off. The solenoids have since been disabled and this kiln is fired manually.

i know there is a formula for chimney height but do you think this kiln may just be different and doesn't need that specified height.

Thankyou

 

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I would not worry to much about the stack height .

Venturi burners are supposed to burn at the tips. Not at the orifice (any chance the orifices are for natural gas??)Propane is alway smaller holes on the orficices. That old potter advice is spot on on the burners

The bottom peep during reduction should have a small lick either constant or now and again.

Anything over 12 hours is a problem

I'm not a propane guy but if the tanks  are freezing (to much gas draw from a single tank)its an easy fix with the water trickle .

I'm thinking gas issue and the freezing is not about air temps but gas exit temps at tank.

Can you get a two tank draw system-or lets see what others with propane are doing-Whats the kiln size again????in cubic feet-it was a small kiln like an 8  or 12 cubic?

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1 hour ago, Mark C. said:

I would not worry to much about the stack height .

Venturi burners are supposed to burn at the tips. Not at the orifice (any chance the orifices are for natural gas??)Propane is alway smaller holes on the orficices. That old potter advice is spot on on the burners

The bottom peep during reduction should have a small lick either constant or now and again.

Anything over 12 hours is a problem

I'm not a propane guy but if the tanks  are freezing (to much gas draw from a single tank)its an easy fix with the water trickle .

I'm thinking gas issue and the freezing is not about air temps but gas exit temps at tank.

Can you get a two tank draw system-or lets see what others with propane are doing-Whats the kiln size again????in cubic feet-it was a small kiln like an 8  or 12 cubic?

No the orifices are not for natural gas. Yes small kiln. 8-9 cubic feet but I need to double check tommorow.

 

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14 hours ago, neilestrick said:

Can you post a picture of your kiln and burners?

Linda posted extensively some time ago.

I'm now wondering re  placement of bag wall and shelf plan  Is the flame path just in and out the backdoor so to speak?

The burners should have a roar to them.

Primary and secondary air I wonder about too

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Ok I found the pics, from back in July. I think it's got to be a problem with either the settings on the burners or the propane line itself, but this is one of those things where it's really difficult to diagnose without actually having my hands on the kiln. I know that's not helpful. I think you need to get someone really familiar with gas kilns to come out and help with the next firing.

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11 minutes ago, Rae Reich said:

@Linda A, when you did the candle test at the bottom peep and the candle went out, was the flame sucked into the kiln or blown out from it?

You should have positive pressure in the kiln. If you don't have pressure, then there's too much being let out the chimney. When you put it into reduction, there will be flame out both spy holes (top and bottom). One will have more flame coming out than the other. The one with less flame should just be a little wisp. The size of the flame out the other will depend on the settings of kiln. As long as you have a wisp out the lesser spy hole, you know you've got pressure throughout the kiln, and that will help it to fire evenly and get even reduction.

Some venturi burners are noisy even if they're not back burning. You need to look and see where the flame is, don't just trust the sound. I would try increasing the air at the burners.

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2 minutes ago, neilestrick said:

You should have positive pressure in the kiln. If you don't have pressure, then there's too much being let out the chimney. When you put it into reduction, there will be flame out both spy holes (top and bottom). One will have more flame coming out than the other. The one with less flame should just be a little wisp. The size of the flame out the other will depend on the settings of kiln. As long as you have a wisp out the lesser spy hole, you know you've got pressure throughout the kiln, and that will help it to fire evenly and get even reduction.

Some venturi burners are noisy even if they're not back burning. You need to look and see where the flame is, don't just trust the sound. I would try increasing the air at the burners.

That's why I asked - she thought the atmosphere was moving too fast through the kiln, I think it's backed-up.

My Venturis make a nice low roar with natural gas. Their intakes are always full open. I think she has a fuel/air mix discrepancy as well as too much fuel while too much damper (easy for me to say, sitting way over here).

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12 minutes ago, Rae Reich said:

That's why I asked - she thought the atmosphere was moving too fast through the kiln, I think it's backed-up.

My Venturis make a nice low roar with natural gas. Their intakes are always full open. I think she has a fuel/air mix discrepancy as well as too much fuel while too much damper (easy for me to say, sitting way over here).

I agree. If the damper can only be opened about 1/4 inch to keep pressure, then the burners aren't putting out enough air to help create pressure. Opening up the burners should allow for opening up the damper more, which creates more air flow through the kiln. But yeah, it's hard to diagnose from afar.

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@Linda A Why have you decided 12 inch WC is the right max pressure? Sounds to low to me and probably why you are stalling at 2000f / 1000c~ Do you know what size orifice the burners have? If it's smaller than 2mm than you won't be getting 60,000 btu gas out the hole.

Edited by High Bridge Pottery

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2 hours ago, neilestrick said:

Ok I found the pics, from back in July. I think it's got to be a problem with either the settings on the burners or the propane line itself, but this is one of those things where it's really difficult to diagnose without actually having my hands on the kiln. I know that's not helpful. I think you need to get someone really familiar with gas kilns to come out and help with the next firing.

Yes thanks that would be helpful but hard to find as everyone is busy.

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1 hour ago, Rae Reich said:

@Linda A, when you did the candle test at the bottom peep and the candle went out, was the flame sucked into the kiln or blown out from it?

From up to 500 degrees the flame was pulled into the kiln.  After that the flame was blown out.

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Keep in mind she lives on an Island and does not have the same resources of land livers.

Sounds like the burners are starved for air-open the flaps at least some next fire.

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37 minutes ago, High Bridge Pottery said:

@Linda A Why have you decided 12 inch WC is the right max pressure? Sounds to low to me and probably why you are stalling at 2000f / 1000c~ Do you know what size orifice the burners have? If it's smaller than 2mm than you won't be getting 60,000 btu gas out the hole.

When I worked for Alpine kilns, they required the gas service to be set at 14" WC, which is double household pressure. 12" should be plenty.

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1 hour ago, neilestrick said:

You should have positive pressure in the kiln. If you don't have pressure, then there's too much being let out the chimney. When you put it into reduction, there will be flame out both spy holes (top and bottom). One will have more flame coming out than the other. The one with less flame should just be a little wisp. The size of the flame out the other will depend on the settings of kiln. As long as you have a wisp out the lesser spy hole, you know you've got pressure throughout the kiln, and that will help it to fire evenly and get even reduction.

Some venturi burners are noisy even if they're not back burning. You need to look and see where the flame is, don't just trust the sound. I would try increasing the air at the burners.

Yes that is what happens when in reduction . .  I had a 4 inch flame out of the top peep and a wisp out of the bottom. The temp also rises at this time.

The way the burners are now there is a nice blue flame with orange on the tips.  That is with the gas fully open. If I open the air vents the burner is noisy and starts puffing. It seems like it has to be almost closed to have a nice steady flame but there is no sound.  It is difficult to adjust the air flaps on the bottom of the burner as the difference between a noisy flame and a quiet flame is only a hair difference.

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2 minutes ago, Mark C. said:

Keep in mind she lives on an Island and does not have the same resources of land livers.

Sounds like the burners are starved for air-open the flaps at least some next fire.

Yes but when I open the air flaps the flame is not steady, it's puffing etc and seems like it may blow itself out which I don't want when I am firing. The difference is so small from steady flame to puffing it's very difficult to adjust any kind of change.

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4 minutes ago, neilestrick said:

When I worked for Alpine kilns, they required the gas service to be set at 14" WC, which is double household pressure. 12" should be plenty.

Orifice is for a propane fired kiln.

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1 hour ago, Linda A said:

Yes but when I open the air flaps the flame is not steady, it's puffing etc and seems like it may blow itself out which I don't want when I am firing. The difference is so small from steady flame to puffing it's very difficult to adjust any kind of change.

Make sure the damper is fully open so it doesn't back out of the venturi, when the flaps are open a LOT more volume of air moves through the burner and it needs to go somewhere.  Start with the damper fully open and adjust the venturi flaps and gas.  Definitely sounds like you're not getting enough air moving through to me.  Loud isn't bad, as long as it's the sound of rushing air and burning and not the sound of flames shooting out of the air ports in the venturi burner

Edited by liambesaw

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OK. Quick check to see if it's a tank freezing issue.  Take a 20 pound propane tank - the kind you use on a gas grill (borrow one from a friend if need be).  A 100 pound tank should have the same valve as a 20 pound tank.  Fire your kiln with the 100 pound tank until it stalls.  As soon as it stalls, turn the gas valves off, swap to the 20 pound propane tank, and turn the gas back on.  (No worries about pressure differences in a 20 and 100 pound tank.  Propane makes it's own pressure by boiling at -43 degrees Fahrenheit.)  The kiln will be hot enough that it will re-ignite the propane as soon as it enters the kiln. Propane ignites between 920 and 1020 degrees Fahrenheit (Some will say "unsafe" - do what you feel safe with.) Try to finish out the firing.  You should only lose a few hundred degrees in all this swaparoo.  I've shut down the kiln, drove to the store to swap out a 20 pound tank, came back home, hooked it all back up, and only lost about 300 degrees.  If it is a freezing issue, this will let you know for sure.

 

Edited by Patrick

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Also, not sure how comfortable you are in messing with the regulators (or replacing them with adjustable high pressure regulators), but a 100 pound propane tank has anywhere between 100 and 200 psi, depending on ambient temps, so you have lots of room here to see if you can get something that works better for you.

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5 hours ago, High Bridge Pottery said:

@Linda A Why have you decided 12 inch WC is the right max pressure? Sounds to low to me and probably why you are stalling at 2000f / 1000c~ Do you know what size orifice the burners have? If it's smaller than 2mm than you won't be getting 60,000 btu gas out the hole.

Linda, just as a point of reference, according to Ward Burners Kiln Cubic Feet and BTUs, if your kiln has 9" of insulating brick (the soft brick), you need approximately 10,000 btu per cubic foot of kiln space per hour.  You have an 8 cubic foot kiln.  That's approximately 80,000 btus per hour to hit cone 6 (APPROXIMATELY).   I haven't checked the orifice size chart, but here it is for your reference.  At 11" WC (I know you have 12" so 11" should be fine),  you would need an orifice size of at least 7/64" (for only one burner!)  to put out that many btus at that pressure(11" WC).  ... That is unless you increase the pressure (which was why I brought up adjustable high pressure regulators in previous post).  More pressure = more fuel = more btu/hour through same orifice.  Don't go voiding warranties or blowing stuff up though! Make sense?

Edited by Patrick

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