[Clayart] forced air burners
vpitelka at dtccom.net
Sun Jul 10 22:47:12 EDT 2016
Becky Holloway wrote:
"I’m trying to get a feel for what is a “normal” experience when firing with forced air burners. Are they easy to use or difficult? Do they stay lit once the thermocouple is satisfied? If you’ve used more than one brand, do you have a favorite? Why?"
Hi Becky -
I think that Ward power burners are pretty much the standard for power burners today. We have them on two kilns and find them very reliable and easy to control. I am curious why you weren't calling Marc Ward through all of this. Why call Baso? It is not a Baso valve problem. Marc Ward designed and builds the burners, and in my experience he has always been very helpful.
Do you have the Ransome venturi pilot burners or the small target pilots like on a hot water heater? With the Ransome venturis, One problem frequently experienced with the Ward power burners is excessive draft (caused by excessive damper opening and inadequate back-pressure) which causes the pilot flame to pull away from the thermocouple and thus the kiln shuts down. If you have adequate back pressure in the early part of the firing, the pilot flame continues to heat the thermocouple and there is no problem. My students occasionally experience this - the kiln shutting down in the overnight preheat, and it is always because the damper is open too far.
Also, if your kiln is equipped with rheostats to control the blowers, don't use them. Just set them on high, and use the adjustable shutters on the blower intakes to control the primary air. If your blowers don't have adjustable shutters, it is easy to install them. That is a much more reliable control of the primary air.
Our downdraft at the Craft Center is our workhorse kiln for cone-10 reduction. If you want, I can email you our handout for firing that kiln. It might help you. I was surprised to hear that the potter who previously had your kiln experienced so much trouble through 45 firings and never figured it out. I wonder if he ever talked to Marc Ward.
For the past 15 years I’ve been firing a potters’ guild kiln that’s about an 18 cubic ft. arched downdraft with 4 Venturi burners; one at each corner parallel to the floor using natural gas. Many happy firings with that kiln.
So, a potter moving out of state was selling a kiln in great condition and I bought it from him. It’s also an arched downdraft kiln about 23 cubic feet, built almost entirely of insulated fire brick and fired with 2 forced air burners using natural gas. The burners are at the back corners. (I believe they are Ward burners in the standard configuration.) He fired it about 45 times and I’ve fired it twice. After digging through his log book I’ve discovered he had chronic problems with the burners--from his first firing to the last. (Less than half of his firings seemed to have been trouble free—no notes indicating he had to re-light one or both burners.)
The first time I fired it we had difficulty keeping the burners lit. We wound up replacing both thermocouples but couldn’t make adjustments to the gas settings without them going out. Got to about 2000 degrees; the kiln bearly moving up temp-wise; shut it off and went to bed. My husband used to work in the heating and air conditioning field and was convinced the
thermocouples were the problem. On the advice of the BASO people, we
purchased and installed a longer thermocouple which put the sensor farther back. The second firing went pretty well—I consider it a successful one; got to cone 10 in about 12 hours (a bit long but o.k.); the pots looked good overall, and we thought our troubles were resolved.
Yesterday we couldn’t get the burners to stay lit. We're calling BASO again--maybe the valves need replacing--and will check our gas pressure but after the last firing we're really puzzled. Ward's website says most of the time it's kiln design not the burners but what's normal for forced air burners? If the gas and air are right, shouldn't they at least stay lit?
Clay Otter Pottery, Alaska
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