Brad Carter on mon 20 dec 04
Hi all,
I'm having problems with a gas conversion kit that I bought from Summit Gas
Kilns in Land O'Lakes, Florida. the conversion kit is a welded steel stand
with manifold, burners and pilot lights. You use it to convert an old,
nonfunctional electric kilns into a gas kiln. You cut four holes in the bottom of
your old electic kiln for the burners and a hole in the top for a vent.
There are models for propane and natural gas.
This is my first effort at firing my own kiln. The problem--at least I
think it is a problem is that the gas is igniting inside the burners (about 2
inches below the top of the burners. But I thought that the gas was supposed to
ignite after it exits the burner. Isn't that how it works--the pressurized
gas mixes with air as it passes through the burner tube and then is ignited by
the pilot light as it exits at the burner tube??? The unit I bought is
burning inside the burner tubes. After a minute the burner tubes, which are
(were) painted red, start to smoke as their paint burns off.
I called Peter (last name Allessi??) at Summit kilns about this problem. He
said "oh yes, it is definitely not working properly" and "I really want to
help you solve this problem." He suggested checking the intake fittings
attached to the manifolds to see if there was some obstruction there. I did
that--no obstruction. He then said he thought the kiln was not getting enough
gas pressure. But I had a local kiln expert over yesterday who said the kiln
was getting plenty of gas pressure. He couldn't figure out what was wrong,
but said that I should try adding a ring to the top of the burner to decrease
the inside diameter just a bit. He thought this would make the gas ignite
after leaving the burner tuber, rather than igniting inside the tube.
Today I talked with peter at Summit Kilns again and he told me the burners
are actually designed to ignite inside the tube. I asked him "Doesn't the
paint all burn off?" He said that's right, that's what happens."
So I am in a quandry. First Peter says the burners are malfunctioning, then
he says they are OK. He told me today to "just fire it." Can anyone offer
me some advise on what I should do?
Best regards,
Brad Carter
Grass Valley, CA
bradcarter@aol.com
william schran on tue 21 dec 04
Brad wrote:>So I am in a quandry. First Peter says the burners are
malfunctioning, then
he says they are OK. He told me today to "just fire it." Can anyone offer
me some advise on what I should do?<
I also got one of the Summit kiln conversion kits some time back for
an old electric kiln at school. Completed all the conversion, but
have yet to fire it up. You should not have the flame in the air
mixing tube.
I do have an Olympic updraft and I'm experiencing the same issue with
flames in the burner, but mine is restricted to the burner part that
is part of the ignition tube - at least I think that's all. Anyway,
another Clayarter, Bob Mesnard, was most helpful in sharing his
experiences with flames in the air mixing tubes of his burners on
his updraft kiln and how he resolved the problem by fabricating a
burner retention tip. He said flames in the tube are due to
insufficient gas velocity.
I originally was going to connect to natural gas, but the contractor
told me the pressure was not adequate for the requirements of the
kiln, and if the gas company increased the pressure, that might cause
problems with the household gas appliances.
Might want to call back to Summit and ask what the orifice size is
they supplied, propane is smaller than natural gas.
Bill
Vince Pitelka on tue 21 dec 04
> This is my first effort at firing my own kiln. The problem--at least I
> think it is a problem is that the gas is igniting inside the burners
> (about 2
> inches below the top of the burners. But I thought that the gas was
> supposed to
> ignite after it exits the burner.
Brad -
Being a certified pyromaniac who, fortunately for society, has found
productive outlets for this fascination, I have always loved burners, in all
shapes, sizes, and applications. The depth of my fascination is perhaps
indicated by my growing collection of sixty or seventy old bunsen burners.
The phenomenon you are rexperiencing is called back-burning, and it is hard
to understand why Peter at Summit Kilns would tell you this is okay. What
kind of burners are on that conversion? Most of the updraft toploader gas
kilns and conversions use the GACO MR-750, the same burner that is popular
for most raku kilns. It is a good little burner, with excellent
flame-retention properties, and it should not be backburning. Any
well-designed, properly adjusted, properly operated cast-iron or fabricated
steel tube or venturi burner should never experience back-burning. That
said, we do have some old Norman gas updraft kilns at the Craft Center, and
they are equipped with refractory clay venturi burner tubes, and at low
settings they do tend to backburn.
Generally, backburning is caused by too little primary air entrained into
the gas-air stream, and/or too little gas pressure at the orifice. If there
is not enough primary entering the burner tube, the speed of combustion
exceeds the speed of travel of the air-gas mixture, and the flame moves back
up the burner tube, often right back to the orifice, creating a smoky
yellow-orange flame. I am assuming that your burners have adjustable air
shutters at the back opening, and you must make sure that those shutters are
open wide enough to admit adequate primary air. You may have to do some
experimentation.
In a tube burner or venturi burner, primary air is drawn in by a slight
vacuum created by the velocity of gas escaping from the orifice. If there
is not enough gas velocity, then inadequate primary air will be entrained,
and the gas-air mixture will move very slowly down the burner tube.
You didn't say whether your kiln is natural gas or propane. If by chance it
is running on propane but with natural gas orifices in the burners, that
would explain the problme. Household natural gas pressure is normally 7 WCI
(water column inches) whereas set-regulated propane is usually 11 WCI, and
thus the propane orifice must be smaller. That's enough to make a big
difference. And if a burner setup is designed to run on an adjustable
propane regulator, then the pressure at the orifice can be as high fifteen
or twenty PSI (pounds per square inch) pressure, in which case the installed
orifice is often smaller still.
This does sound like a problem either with the orifice size, the gas supply
pressure, or the primary shutter settings. Open up the primary air shutters
and see if that has any effect. Make sure that your burners have the right
orifices for the kind and pressure gas you are using. If you are using
propane, make sure the set-regulator or adjustable regulator has sufficient
capacity for your burners. If you are using natural gas, make sure that the
supply line is of adequate size for the burner system.
If you can tell us more about the whole setup, we can help you diagnose the
problem.
Good luck -
- Vince
Vince Pitelka
Appalachian Center for Craft, Tennessee Technological University
Smithville TN 37166, 615/597-6801 x111
vpitelka@dtccom.net, wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka/
http://www.tntech.edu/craftcenter/
william schran on wed 22 dec 04
Vince wrote:>The phenomenon you are experiencing is called
back-burning, and it is hard
to understand why Peter at Summit Kilns would tell you this is okay. What
kind of burners are on that conversion? Most of the updraft toploader gas
kilns and conversions use the GACO MR-750..... Any
well-designed, properly adjusted, properly operated cast-iron or fabricated
steel tube or venturi burner should never experience back-burning. That
said, we do have some old Norman gas updraft kilns at the Craft Center, and
they are equipped with refractory clay venturi burner tubes, and at low
settings they do tend to backburn.<
The burners on the Olympic updraft and Summit conversion system are
the cast metal bottom with steel pipe. The Olympic burners have
adjustable metal disks/bells for primary air adjustments, the Summit
has no primary air adjustment capabilities. Have one of these
conversions done at school, but have not tried firing yet.
The Olympic I have has 3 burners and an ignition tube with a back end
that is a burner bottom with the ignition pie welded to it. Had not
noted back burning in the burners, but flames will lick out the back
of the ignition tube assembly/burner when the burners are lit. Before
the burners are lit, there's no back burning. The ignition tube,
besides lighting the burners, also keeps the thermocouple of the Baso
valve heated.
Tried many settings, but simply can't get the back burning of the
ignition pipe to stop. Suspect poor design and that the system runs
on low pressure - 11"w.c. Had to adjust the regulator to a lower
setting, otherwise the whole system would shut down (assumed too much
pressure for 1/2"psi rated Baso valve)
Plan to retrofit using MR750 burners (ordered prior to Vince's post)
and a target pilot for Baso valve attached to first burner, bypassing
the ignition tube. These burners are same length as existing burners,
so should be no problem switching out. Spoke with Marc Ward (where
I'm getting the stuff) and we're sticking with #40 orifices.
Bill, Fredericksburg, Va, where we had very cold, windy, snowy
weather Sunday night.
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