Elaine J. Walters on mon 29 jul 96
Dear Raku persons!
I've had my raku kiln for over a year- had really nice results- things going
great. Then I decided to get a larger tank-50 gal. and new regulator. My kiln
is a 20 gal expanded metal with pulley system. Set the p.s.i. @ 7. No matter
what I try I am getting at least 2" of flame, sometime more, coming out of my
flue and I seem to be overfiring--getting really shiny coppery glazes where
before I got some very nice matts. I've tried adjusting firing times, air, etc.
but to no avail. Am I overpowered? The only other thing I haven't tried is
enlarging my flue. I don't like my glaze results, since I am reducing a lot in
the kiln. Glazes I used to fire at 1850 F, are underfired with bubbles @ 1825
and overfired at 1850 and I can't look in the flue to check melt because of
flame. Any suggestions you can give me would be greatly appreciated. I have
some shows coming up and I'm getting desperate! Help!
Elaine, on Camano island, where our hot spell has finally broken.! Fog came in
this morning>
WardBurner@aol.com on mon 29 jul 96
Elaine,
You didn't indicate what type of regulator you were using before (i.e.
pressure & volume). If you were using a low pressure regulator before, your
orifice is probaly not sized correctly for high pressure (anything over 1
PSI). If the old reg. was for 11" water column, you are putting more than 20
times the pressure through an orifice that is now much too large in relation
to the pressure increase. I also need to know what kind of burner you have. I
help folks with this problem frequently. If you buy an inexpensive Venturi
such as a Gas Appliance MR750 (this is the little 8" long "dumb bell" looking
burner that many places sell as a Raku burner) you might have orifice
problems. What happens is many suppliers buy these guys from Gas Appliance
Co. (GACO) and order a natural gas or a propane orifice. These orifices are
for use with low pressure. When you run high pressure through them, they can
not inspirate enough air and reduce like gang busters. On burners that I
don't manufacture, I always order Venturi's with blank orifices and then
drill them to the customers application. If the folks that are selling you
burners don't understand the relationship between orifice/pressure/throat
size, you might want to seek advice on the correct setup. More expensive
Venturi burners such Ransome, Pyronics, Eclipse, Hones, ect. can handle high
pressures (up to 30 PSI) because they have longer throats and have a much
higher quality casting. The smoothness of the interior reduces turbulence and
increases inspirated air. The are set up for varying degrees of high pressure
or low pressure. Because of this, expensive burners have a wide range but may
have a smaller output on low pressure than the GACO MR750. Give me a call so
we can discuss your problem and get you up and running.
Marc Ward
Ward Burner Systems
PO Box 333
Dandridge, TN 37725
423.397.2914 voice
423.397.1253 fax
wardburner@aol.com
Elainr wrote:
<<<<< Set the p.s.i. @ 7. No matter
what I try I am getting at least 2" of flame, sometime more, coming out of my
flue and I seem to be overfiring--getting really shiny coppery glazes where
before I got some very nice matts. I've tried adjusting firing times, air,
etc.
but to no avail. Am I overpowered? >>>>>
BobWicks@aol.com on wed 31 jul 96
Hi Elaine:
I suggest that you reduce your gas pressure to about 3-4 lbs, and pull the
burner out a bit to increase secondary air , and possibly change the flue
opening. Try each of these separately and then in combination until you get
what you want. The fact that the flame is coming out of the flue definitely
tells me that you have the gas/air mixture incorrectly set. Start by
reducing gas pressure..then increase secondary air.
Good luck
Bob
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