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Post by pasto76 on Jan 8, 2012 20:48:44 GMT -8
using 6 inch system. burn tunnel is 8 inches, feed box is about 8 inches. Riser is 32 inches, 2 inch gap down the sides as well as 2 inch gap on the top. I had to bring down a 55 gal drum to a 16" diameter, so I have the lid loose. Ive been playing with increasing or decreasing the top gap all afternoon and night now. When the lid is off, the draft is extremely robust. As soon as I put the lid on, really with any sized gap, it reduces significantly. Some positions are worse than others, but even the best isnt that good. Having gone back through many many threads this afternoon, Im rather stuck. Is there something Im missing?
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Post by Donkey on Jan 9, 2012 8:35:42 GMT -8
So, yer feeding a set of 6 inch bench guts from an 8 inch rocket stove?? If so, that's yer problem. If not, I guess I didn't understand your description..
All things being equal, I'd look at where the barrel connects at the bottom. That space down there needs to be larger than is at first imagined.
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Post by Donkey on Jan 9, 2012 8:37:33 GMT -8
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Post by pasto76 on Jan 9, 2012 9:31:56 GMT -8
Hello, the tunnel and feed length is eight inches. Everything else is the same CSA, +/- .10 of an inch.
The bottom of the bell is open currently. I had thought of this yesterday and dug out some stuff to ensure that there is more than enough room for everything to vent..is it possible it's too loose and needs to be collected into the exhaust duct?
The helpful hint thread has been very useful. To let you know, Ive spent many hours reading this forum and the RMH stuff on permies (even alloyavenue forums have helped me with some things). I take notes when someone says something important. Example, the other day when I found the draft diminishing, I spent hours re-reading tons of posts here. I found some mentions by you that the dimensions suggested in the book can be bigger than what they have printed. My main concern is whether a 2 inch gap down the sides is too big...actually having just re-re-read a post here saying that the diameter of the bell should be measured at the ridges, which would make the side gap I have 2.5 inches or bigger.
I also just re-re-re-re-did the "divide CSA by circumference of the riser to get the top gap" and got 1.5 inches. An error previously Im guessing gave me 2 inches. I have things set up now the gap can be 2 inches or larger. I will have to change some things to try 1.5 inches. Maybe I will try a clay ring spacer before making serious changes to my setup.
Thanks!
on edit: spurred by a response on another thread, I found that I have an error in my build. Burn tunnel is 5.25 x 5.75 inches which gives it a CSA of 1.92 square inches bigger than the CSA of the 6 inch round duct. which makes sense if the gases are expanding, AND I had just a little pulsing which can indicate a bottleneck somewhere, yes?
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Post by Donkey on Jan 10, 2012 8:15:49 GMT -8
The bottom of the bell is open currently. I had thought of this yesterday and dug out some stuff to ensure that there is more than enough room for everything to vent..is it possible it's too loose and needs to be collected into the exhaust duct? ?? Not sure I understand the question. I don't know if it's possible to have too much space down there.. OK, theoretically you probably can, but as a practical matter I just don't see it happening. On the barrel, too big is fine, too small IS NOT. I've noticed they run better with more space in the barrel area (in every dimension) rather than less. Also, since you are not using a 55 gallon barrel (at least NOT AS 55 gallons) the critical measurements have changed. The measurements in the book are designed for THOSE PARTS. If you change the size of the parts, you gotta check the measurements.You said you've cut down a barrel to a 16 inch diameter.. Assuming you mean 16" measurement at the NARROWEST point inside the barrel, and assuming the gap between the inside of the barrel and the WIDEST point on the outside of the heat riser jacket is 2" all the way around: This tells me that the heat riser (jacket) has a 12" diameter. What has to be done is figure the cross section area of the two measurements and subtract the inner on from the outer one to find out if you got enough space. The inside area of the barrel is 200.96 square inches. The outside area of the heat riser jacket is 113.04 square inches. The gap between the two should have an area of 87.92 square inches. Six inch pipe has an area of 28.26 sq. in. so you got plenty of room and some to spare. That burn tunnel is not helping you AT ALL. You gotta narrow it down. Often the pulse indicates a bottleneck, yes. I'd fix the burn tunnel first, then if you still got issues, go looking for a pinched spot.
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Post by pasto76 on Jan 10, 2012 15:36:48 GMT -8
right on all counts. I put some tile shims in the bottom of the burn tunnel to bring that CSA a little below that of the 6" riser. I also had to spend some time and change some things to bring the bell down, and now have a top gap of a touch bigger than 1.5".
I ran it for about 2 hours. No smokeback. No pulsing. What I am definitely calling a much stronger draft. Going to replace the tile shims with a few slices of firebrick. Thanks for your input!
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Post by pasto76 on Jan 16, 2012 7:38:09 GMT -8
a shot of the finished stove. She seems very happy and is eating wood with gusto.
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