Shez Posted October 2, 2020 Report Share Posted October 2, 2020 I’ve recently built the power kiln from Andrew Holden’s ‘self reliant potter’. I’ve built one years ago and it was great. This one is firing fine, good reduction etc but the temperature range from top to bottom of the kiln is too wide. Cone 10 fully down at the top = cone 9 just starting to bend. I’ve tried soaking at the end of the firing to no significant effect. it’s a bit frustrating - any ideas or suggestions? Link to comment Share on other sites More sharing options...
Sorcery Posted October 2, 2020 Report Share Posted October 2, 2020 Having a dual or quad zone therm can help you understand what damper actions do to your temps high and low. They say pull it out to heat the bottom ( I think) and push it in to heat the top. I'd test things at the in between and see if it's even a problem. I have been loading 8-10 firings and 6-8. Seems more mass will knock cones down faster, so you may be able to pack the bottom heavier. A flame deflector just before the flue may help, wait...updraft or downdraft? Sorce Link to comment Share on other sites More sharing options...
Shez Posted October 2, 2020 Author Report Share Posted October 2, 2020 Thanks for helping. It’s a down draft kiln. Link to comment Share on other sites More sharing options...
neilestrick Posted October 2, 2020 Report Share Posted October 2, 2020 Can you post pics of the kiln? Interior, exterior, burners, etc. I'm not familiar with that particular build, and even if I was it's usually necessary to see just how you've got it set up. Link to comment Share on other sites More sharing options...
Shez Posted October 2, 2020 Author Report Share Posted October 2, 2020 It doesn’t seem to allow me to upload pictures here!! I’ll keep trying. in the meantime it’s a 5cuft kiln and the flue opening is 23.5sq” Link to comment Share on other sites More sharing options...
Shez Posted October 2, 2020 Author Report Share Posted October 2, 2020 Link to comment Share on other sites More sharing options...
Shez Posted October 2, 2020 Author Report Share Posted October 2, 2020 Link to comment Share on other sites More sharing options...
neilestrick Posted October 2, 2020 Report Share Posted October 2, 2020 So the flue opening is down below the shelf, and runs up through the bumpout in the back wall, correct? Since you're using atmospheric burners and it's running hot at the top, I would say that you need a taller chimney for more draw. Link to comment Share on other sites More sharing options...
Shez Posted October 2, 2020 Author Report Share Posted October 2, 2020 Yes that’s correct. there’s no requirement for a longer flue in the design - do you think that would help? Link to comment Share on other sites More sharing options...
liambesaw Posted October 2, 2020 Report Share Posted October 2, 2020 I don't even see a chimney on there, is that by design? If it's a downdraft you need draft, which means you need a chimney Link to comment Share on other sites More sharing options...
neilestrick Posted October 2, 2020 Report Share Posted October 2, 2020 7 hours ago, Shez said: Yes that’s correct. there’s no requirement for a longer flue in the design - do you think that would help? Lots of old designs out there that don't necessarily work great. More chimney height = more draw, which will pull the heat down better and even things out. Did the old one have the same problem? Same setup, burners, etc? Link to comment Share on other sites More sharing options...
Shez Posted October 2, 2020 Author Report Share Posted October 2, 2020 The one I did originally was exactly the same design. The only possible variation are the burners. It’s a fairly famous book and the design is well proven. I wonder if I need to speed up the early part of the firing to encourage draft? Link to comment Share on other sites More sharing options...
Mark C. Posted October 2, 2020 Report Share Posted October 2, 2020 Looks like downdraft with no chimmney to aid in draft. You can change the stacking to control temp you can add a small chimney to add draft-and control temp you can mess with the flue opening to control temp if I owned it I would add some draw with a chimney -its easy and simple to do. Link to comment Share on other sites More sharing options...
liambesaw Posted October 2, 2020 Report Share Posted October 2, 2020 I think I've heard of this design. The internal chimney is supposed to get so hot that it creates a convective current. Problem with that is that at high temperatures convection gets weaker as the air gets thinner. Link to comment Share on other sites More sharing options...
C.Banks Posted October 2, 2020 Report Share Posted October 2, 2020 Gas Kiln Conversion - Downdraft The design works for S.M. Boris Robinson Link to comment Share on other sites More sharing options...
neilestrick Posted October 2, 2020 Report Share Posted October 2, 2020 @Shez Is there any method for adjusting the air on your burners? It's difficult to see how they work from the photos. Where do they pull air in from? Link to comment Share on other sites More sharing options...
liambesaw Posted October 2, 2020 Report Share Posted October 2, 2020 44 minutes ago, neilestrick said: @Shez Is there any method for adjusting the air on your burners? It's difficult to see how they work from the photos. Where do they pull air in from? If you look at the far one you can see the venturi at the back by the valve Link to comment Share on other sites More sharing options...
neilestrick Posted October 3, 2020 Report Share Posted October 3, 2020 22 minutes ago, liambesaw said: If you look at the far one you can see the venturi at the back by the valve Is that L shaped bracket the air adjustment? Could be a lack of pressure in the kiln making it fire unevenly. Adjustments to burners or damper could fix that. It's tough to diagnose gas kilns without seeing them in person, unless it's a glaring problem. Link to comment Share on other sites More sharing options...
liambesaw Posted October 3, 2020 Report Share Posted October 3, 2020 Yeah it looks like the L bracket has a bolt in it for adjusting the orifice in and out. I've seen that style of venturi on forge burners but not on kiln ones. Suuuuuuper touchy Link to comment Share on other sites More sharing options...
Mark C. Posted October 3, 2020 Report Share Posted October 3, 2020 This kiln is in the UK I'm guessing so keep this in mind on material suggestions Link to comment Share on other sites More sharing options...
oldlady Posted October 3, 2020 Report Share Posted October 3, 2020 shez, no kiln info here, just a question. i have not seen holden's book for over 25 years. is this the kiln he designed to use with filtered used cooking oil? it always intrigued me how simple it might be to build and use. Link to comment Share on other sites More sharing options...
Shez Posted October 3, 2020 Author Report Share Posted October 3, 2020 It’s not the one firing with oil - but that’s in the same book Link to comment Share on other sites More sharing options...
Shez Posted October 3, 2020 Author Report Share Posted October 3, 2020 Ref the burners - they do have an air adjustment on them (picture below) The primary air adjustment is a little threaded washer that you can wind back and forth. i have been shutting this primary air off completely as I start reduction. I wonder if this means that the resulting lazy, yellow flame doesn’t have enough pressure to drive circulation through the kiln? Link to comment Share on other sites More sharing options...
Shez Posted October 3, 2020 Author Report Share Posted October 3, 2020 I guess that I could try leaving the primary air open and managing the reduction by restricting the flue during firing. (I do that already but assumed that management of the primary air would be essential). Link to comment Share on other sites More sharing options...
Mark C. Posted October 3, 2020 Report Share Posted October 3, 2020 27 minutes ago, Shez said: I guess that I could try leaving the primary air open and managing the reduction by restricting the flue during firing. (I do that already but assumed that management of the primary air would be essential). Yes I would try that-use the damper for reduction.At least for test fire Link to comment Share on other sites More sharing options...
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