[Clayart] fast fire clarification

Hank Murrow hmurrow at efn.org
Thu Oct 6 01:01:57 EDT 2016

Dear Sumi;

Once again Vince gives a very complete description, this time of the differences between these two types of natural draft mixers. I say mixers, because that is what they do___ mix the fuel(gas) with incoming air. The best of them(I use Eclipse atmospheric mixers) use the gas jet itself to entrain primary air, which is controlled in volume by the air shutter. incidentally, I have seen air shutters opened wide, despite the manufacturers' suggestion (in the case of Eclipse) that 3.5 turns is full air. More than that creats turbulence which reduces efficiency. Anyway, the machined throat that Vince cites is a low pressure area which draws air into the mixer in a very effective way. The capacity of such mixers can be doubled by designing a conical section burner block(using castable refractory), the opening of which is ¾" larger in diameter than the flame retention tip itself, thus controlling the flow of air around the tip and cooling it at the same time. Eclipse Mixers are a thing of beauty, IMHO. Many on this list probably think I am paid to praise their product; but no, I pay almost the same $$$ as anyone, save that I buy in volume, because I am an 'occasional' kiln builder. Not many potters are able to consider $28,000 for one of my Doorless Fiberkilns these days, though in the long run the Shadbolt Center in Burnaby BC has experienced very low operating costs with theirs after 2000+ firings. "No brag, just fact". I guess you can see that I am a proud kiln Papa! 

Anyway, kudos to Vince and others on this list who respond so generously with carefully considered posts.

Cheers from Sasayama, Japan, where I am assisting John Dix and Ty Billman in preparations towards firing John's lovely anagama from the 27th to the 31st of October. While the kiln cools, we'll visit Tanba, and other pottery villages and museums in this area(between Kobe and Kyoto). Soon, I will figure out (again!) how to post pics so all who are interested can enjoy what I see every day.

Hank Murow

On Oct 6, 2016, at 10:08 AM, "Vince Pitelka" <vpitelka at dtccom.net> wrote:

> Hi Sumi - 
> Natural draft burners are either tube burners or venturi burners.  The former generally have a flared intake and then a straight tube, usually with a flame-retention tip creating turbulence to keep the flame right at the tip.  Venturi burners have a flared intake and then a streamlined restriction in the burner tube, and then usually a flame-retention tip at the output.  The gas jet at the back end of the burner is aimed directly at the venturi restriction, which assists with entrainment of primary air and with the intermixing of air and gas.  Both types of burners generally have some sort of shutter at the air intake to control primary air.
> - Vince

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