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Post by satamax on Aug 13, 2015 12:55:25 GMT -8
Why not use that tube, if it does the job! Put some concrete blocks as you've done, but on a larger base, , make a brick plenum above, the tube on top. Hold the tube whichever way suits you. And brick the whole thing outside for looks. May be between bricks and tube, you could stuff insulation  |
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Post by martinpolley on Aug 14, 2015 1:30:59 GMT -8
There are a few arguments against  . First, I have it agree with my wife that it's kinda ugly. Second, it's a bit short. Third, it's really heavy. It must weight 50 or 60 kg. I definitely wouldn't want it to fall on my head! And lastly, it's too narrow. The internal diameter is only six inches, and this is a seven-inch J. I'm sure a seven- or eight-inch pipe would work even better. But I do like your idea of a brick plenum (or something similar). I think it will hold the pipe more securely than just cobbing an elbow into the existing hole (which is what I was planning to do originally). |
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Post by martinpolley on Aug 21, 2015 9:53:28 GMT -8
My brother-in-law and partner in crime got some sections of galvanized pipe off his brother. It's only 16 cm in diameter, but I think it will do the job:  I've cobbed one section into the plenum I built, and will connect the rest of it tomorrow once the cob has stiffened up enough. Then I'll run a test and see how it goes. |
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Post by tallgrass on Aug 21, 2015 20:59:22 GMT -8
How is your manifold designed to transition from heat riser to oven floor? Im also wondering if the bell/oven cavity was made slightly larger if you could bake on top of a grate with a more efficient air stratification via free fas movement. Looks good! Did you install a trip wire and a peter plate on this j tube? Those small touches could also help with the smoke if they were left out.
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Post by martinpolley on Aug 21, 2015 23:42:37 GMT -8
tallgrass Around the top of the riser, there are eight tunnels made of cob that take the hot gases out to a channel that runs around the inside of the dome:  The combined CSA Of the tunnels is a little bit more than that of the riser. I closed it off using an adobe slab with cob to fill the gaps. On the right here you can see the opening where the gases exit the dome:  It's already high enough, I think. A grate would work. Or a big (but thin) pizza stone on some spacers. Maybe I'll try it if I can't get the floor hot enough. There's no P-channel/plate or tripwire here. Can they be retrofitted? How would I go about doing that?
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Post by satamax on Aug 22, 2015 1:44:59 GMT -8
Martin, can you post a pic of your firebox from the front?
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Post by martinpolley on Aug 22, 2015 2:28:08 GMT -8
Sure  Here's what it looked like in action last night, with just a short section of flue as chimney. (I'll attach the rest today, now that the cob around the base is hard.) vimeo.com/136999710 |
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Post by satamax on Aug 22, 2015 6:01:37 GMT -8
Oh, it's a J tube! Pish easy to retrofit a P channel in there. take a piece of thick steel do two cuts on each side, bend thoses two pieces perpendicular to the cut, so they act as spacers against the front of the feed tube, and make the piece of steel deep enough for it to underhang 11mm into the burn tunnel. the pieces on top which are not bent act as ears to hold the whole thing from falling. use a vice to bend it. Here's a better explanation. www.permies.com/forums/posts/list/30134#235482 |
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adiel
Junior Member
Posts: 119
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Post by adiel on Aug 22, 2015 6:27:07 GMT -8
from your pic i really think it is the downdraft opening to the chimney.
can you make it bigger?
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Post by martinpolley on Aug 22, 2015 11:40:49 GMT -8
satamax That sounds fairly straightforward. Thanks! I don't have any metalworking tools or skills, but I know someone who does… adiel It would have been much easier before I added the chimney . But still possible, I think. But now, with the chimney, it's working MUCH better. As I write this, it's been burning three hours now, and the temperatures are still rising. Which makes me extremely happy . Do you think increasing the size of the opening will improve performance even more?
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Post by martinpolley on Aug 23, 2015 10:37:59 GMT -8
satamax With the p-channel/plate, does the shape of the bottom part matter much? I mean, should it be straight, parallel to the front of the feed tube? Or would there be some benefit in bending it to 90 degrees so the air would be encouraged to flow along the top of the burn tunnel? Apart from protecting that first firebrick and ensuring there's enough space for air to get in, is the point of the p-channel/plate to get more air further downstream in order to improve secondary combustion? Or am I not understanding something here?
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Post by satamax on Aug 23, 2015 10:58:41 GMT -8
satamax With the p-channel/plate, does the shape of the bottom part matter much? I mean, should it be straight, parallel to the front of the feed tube? Or would there be some benefit in bending it to 90 degrees so the air would be encouraged to flow along the top of the burn tunnel? Has to be straight and overhanging about 11mm bellow the burn tunnel ceiling, to create a turbulence and draw air in. Also to mix that fresh air and the burning gases. Apart from protecting that first firebrick and ensuring there's enough space for air to get in, is the point of the p-channel/plate to get more air further downstream in order to improve secondary combustion? Or am I not understanding something here? Dat's exactly that. |
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Post by martinpolley on Aug 24, 2015 2:44:59 GMT -8
Thanks! How big should the space between the plate and the first brick be for a 7" J?
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Post by satamax on Aug 24, 2015 3:23:46 GMT -8
5 to 10% of heat riser CSA.
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Post by martinpolley on Aug 24, 2015 3:37:25 GMT -8
Thanks man |
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. First, I have it agree with my wife that it's kinda ugly. Second, it's a bit short. Third, it's really heavy. It must weight 50 or 60 kg. I definitely wouldn't want it to fall on my head! 
