Gas firing question

[Linda A]

Hello all

i have a question that I need some answers to.

How is firing a gas kiln at a set rate per hour to a final temp achieved.   

Is this set rate achieved by controlling the size of the flame coming out of the burners. ( I have 2) or is this set rate per hour achieved by shutting the burners on and off to maintain the temp rise.

Or is it neither of the above and I am way off base.  

Any replies much appreciated.  I need to settle this argument once and for all with my partner.

Thanks     Linda

 

 

 

 

[Mark C.]

To control the rise you use the gas burner valve to add more or less gas. This is for natural draft burners not forced air (blower with gas)burners .

So to get hotter faster you add more gas but turning the valve  on more or to slow turn the gas valve down(I always have the air damper on each burner open all the way )I never touch that air control on the burner.

During the fire I NEVER turn off the burners-repeat NEVER. you turn them up or down..

You learn quickly how fast the fire goes as it depends on the load and how much reduction.

My fire last 10-12 hours for good glaze results .

You can fire as fast as the furniture and ware can take it to some degree-its not like an electric with set climb. I like a 10 hour fire or longer so near the end its going slow enough for the glaze to form crystals and than cool as slow as I can (close damper and block off gas ports to promote slow cooling so glazes mature well.If you have kiln with burners pointing upwards under floor(most updrafts) you will not be able to cover the post so do not worry about that after Turing it off.

[Linda A]

Thanks Mark.  You are very helpful.

i assume you fire to cone 10 for a 10 to 12 hour firing.  I am planning to fire to cone 6.

Do you have any experience with digital controllers.  Do you know if they work the same way, ie automatically controlling the amount of gas coming in  depending on what temp rise has been inputted into the controller?

i do have a controller but it seems it is not working properly so I was hoping I would be able to bypass it and just fire manually.  Do you know if that would be possible.

Again thanks for your help

Linda

[Babs]

Manual is what I used to fire gas.

Record the increase in psi as gas is turned up each hour and note the temp rise and range/ hour also.

Damper opening and closing can affect temp rise also.

Never turn gas on and off .

In fact your burner should have probe linked to it which automatically turns off gas supply if flame stops .

Primary and secondary air supply factors in too.

There are computer controlled gas kilns but adc one never ventures far from a kiln firing...I never bothered with one

[Linda A]

Thanks for the info

[Mark C.]

16 hours ago, Linda A said:

Thanks Mark.  You are very helpful.

i assume you fire to cone 10 for a 10 to 12 hour firing.  I am planning to fire to cone 6.

Do you have any experience with digital controllers.  Do you know if they work the same way, ie automatically controlling the amount of gas coming in  depending on what temp rise has been inputted into the controller?

i do have a controller but it seems it is not working properly so I was hoping I would be able to bypass it and just fire manually.  Do you know if that would be possible.

Again thanks for your help

Linda

Yes I'm firing to cone 11

No experience with a gas digital controller but My potter friend has one on his Geil kiln. It just turns up the gas valves and puts a hold (turns down the gas at ant set point)I'm sure your controller just operates a solenoid (meaning lets more or less gas into burner) depending what you have inputed into controller.

I'm sure the bypass will work but its best to talk to manufacture unless they are long gone?

You could take out the solenoid in the plumbing then its a all manual system.

I fire manually -seat of your pants guy myself.

Live by the flame and die by the flame

[postalpotter]

Linda A 

 Hey, 

 Well as I have said I am a complete novice at this. My only experience with a gas firing is the test fire I did after the kiln was built. I still have not done a bisque fire calibration as described by Steve Davis in the July/Aug. PMI.

My experience with the test firing was that I left the pressure the same, 3WC from 920deg. to 1960 without any need to add more fuel by just adjusting the damper. I got the rest of my increase after 1960 deg. by adding fuel and working the damper open by as little as an 1/8 of an inch. I did increase the gas pressure by as much as another 4in. WC before I ran low on pressure. I finally toped out at ^3.

 I did that on the last day of my vacation and I did it in the daylight where I really couldn't watch the flame.  When I can make the time to fire at night I will follow Davis's article and do the bisque calibration.  

If I remember form your previous post you have an electric kiln so I doubt you have a need to do a gas bisque.

[Linda A]

Hello

Thanks for your advice Mark and Postal potter.

Well I tried to do a test fire today after numerous false starts the last few days.   Did not turn out well

Firstly the pilot light wouldn't stay lit so that got fixed.  Then the solenoid were sticking and buzzing, but now  hopefully that seems to be fixed.  The digital computer panel is finally working correctly.

One  of the Venturi burners had a partly plugged port but is now running perfectly.

Seems like buying a used kiln ( barely used) but still 20 years old will have a lot of glitches with electrical connections and corrosion.  I am keeping my fingers crossed that the solenoid will be ok as everything else seems great.

So today I decided to do a test firing of some glaze tiles. I wanted to fire to cone 6.  Everything was going fine for the first three hours, but by the forth hour it was apparent that each hour the heat increase was lessening from 230 degrees F per hour to 70 degrees F per hr.  The kiln was increasing temp slowly but at the rate I was going I would have had to fire for 8 more hours and used up 100 pounds of propane.  And I think eventually the kiln would have stalled. So shut off at 1400degrees F.

Back to reading info from Mark Ward.   Seems like my draft is non existent.  My chimney is only three feet high.  Needs at least another 8 feet added it seems and then I should have a good temp increase.

Am I correct in my assumption?

I have Venturi burners which were showing a blue flame at the bottom with orange on the tips.  Is this what the flame should look like

Also what should the pressure regulator be set to on my propane tank.  My gauge shows 4 psi.

Thanks in advance for any advice.

[Mark C.]

I need a photo of this kiln for chimney advice-the flue and the chimney.

Is this the one that you had photos of about the bottom shelve?I answer a lot of question and maybe that was your kiln. If so I never saw the back stack.

[Linda A]

Hi Mark

Yes this is the one with the bottom shelves we talked about. I will send you a picture tommorow. 

Thanks.    Linda

[Linda A]

Hi Mark

Yes this is the one with the bottom shelves we talked about. I will send you a picture tommorow. 

Thanks.    Linda

[Linda A]

Hi Mark

Here are the pics of the chimney and flue.

Thankyou

[postalpotter]

Linda A.

 Knowing nothing of what I speak. I would say you are on the right track, Ward figured I would need a stack a minimum of 8ft. from the floor of my kiln.

I will say you have come to the right place for sound advice just a key stroke away. 

[postalpotter]

Love your kiln.

And Yes I am now truly jealous! 

[Mark C.]

I suggest adding about 6-8 feet of stack length . It can be metal or brick to metal with a flue liner like postal potter has.

Just remember if you do the last option you needs to keep those flue liners dry from the rain.

Metal is the easiest option usually.Salvage yards are a good start.I have no idea where you are located? Canada?

[Linda A]

Ok. Thanks a lot.

Yes I live on Canada and can get some metal pipe easily.

 

Postal potter don't be jealous.  Wait until I see if I can even get this thing to temp  and maybe produce something one day.

 

my other question, should the propane coming out of the tank be at a higher pressure than 4.  That's what my gauge shows.

Thanks.    Linda

[postalpotter]

Linda A.

What are you using for a regulator? If it is the same type as type you would use for your propane bar b que that probably is the reason  you can get just 4lb of pressure. 

BUT what do I know. The reason I come here and type is that it is the only way I have to test my assumptions.

 From Mark Ward: http://www.wardburner.com/regulators.html

also: http://www.wardburner.com/draft.html

[postalpotter]

And I have earned the right to a bit of envy!

[Linda A]

Ok. Thanks.  I'll check out the link.

 

[Linda A]

My regulator does not look the same as one from the bRbecue.  It looks much more industrial.

i could include a picture if needed.   It also looks like there is some other type of regulator further down the line.

Anyone have any ideas why I would have two.

thanks.   Linda

[Mark C.]

one should be at the tank the other is part of the kiln plumbing system?

[Linda A]

Yes,  I am enclosing pics.

one is part of the plumbing and one is at the tank.

Is there a way to increase pressure at the tank or should I leave it alone.  

[postalpotter]

Linda,

 Who manufactured your kiln maybe you could contact them ? Or perhaps there might be an owners manual already on line.  Pictures of the gas lines and associated valves  might help.

Also reposting your question under a new title might grab the attention  of someone else

 

[postalpotter]

Hello Linda,

 Yea if you are reading your pressure at the bottles then that regulator with the gauge is the place to start. If you read ward's short post on regulators then the rubber diaphragm  could be bad. 

 Me I just don't know but for the price of your kiln just change the whole package. the regulators should be an easy purchase.  

[Linda A]

Kiln not being manufactured anymore.  Nothing online.

Yes, I will try reposting my question .

Thanks