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UDS Question, this puzzles me

post #1 of 10
Thread Starter 
Ok you UDS gurus, this one is right up your alley.

I've built several UDS recently, and I would like to think I at least have an understanding of how they work. Each of my first 4 drums was built using four 1" intakes using either 3/4 nipple valves and caps/ball valves or flexable magnets over the holes to regulate temperature.

My recent dilema is this:
Today I made two breakfast fatties, fired up the smoker and cooked. This smoker (#5, see previous postings for burn tests and whatnot using smaller intakes) has four 3/4 holes and uses magnets to cover the holes and regulate temperature, no biggie, been smoking on this one at work for over a month now, probably about 10 times or so. Today after I cooked on it, I pulled the meat around noonish and covered the vents completely and put the lid back on didn't cap the exhaust. Went outside just a bit ago (around 3pm CST) and the temp was holding at 200-210 degrees with no other primary intakes open. The lid isn't exactly an airtight seal, but it seals evenly all the way around. Is there any reason why with it using the exhaust as both a air draw/exhaust push that I couldn't cook on it as it is and not experience any temperature fluctuations and for it to maintain the same temperature that it's holding now?
post #2 of 10
I have a cover with a wing nut over my exhaust, and the same over my intake, and after a cook I can close them both and the coals will die almost immediately..

With what you described, I doubt that it would hold those temps for a prolonged period of time..

With a separate intake and exhaust, when the warmer air rises and exits through the exhaust, it creates a vacuum effect to suck air in through the intake..
post #3 of 10
Thread Starter 
It has before. This isn't the first time it's done this, just the first time I've actually paid attention to it. The first time it burned completely through the night at that temperature and when I came and checked it the next day, the fuel was literally all used and burned up.

On a separate note, i'd like to know who built yours for you as I really admire the build and would like to get one done as well. I'm very limited on parts and skill.
post #4 of 10
Fellow SMF member ratdawg built mine.. I was going to do my own a no-weld build, until I saw the quality of his builds, and he lives in my area..

I don't know how you could improve upon his builds.. Locks in temps effortlessly, for 15 hours on my seasoning burn, and very fuel efficient, as I can shut it down after a cook and save the coals, and wood, for the next smoke..
post #5 of 10
Thread Starter 
I can do the same on the ones that I built that are similar to yours, just not as nice looking. I was just curious as I don't have the talent to produce near the quality that his are.
post #6 of 10
Well . . . yes and no. You could probably have it hold "a" temperature, but it probably wouldn't be as high as it was when you observed it or high enough to cook the food safely. Since the UDS was empty, there was no heat sink to absorb the heat. There was also nothing in the way to obstruct the air flow. With the drum completely empty you were likely getting a draft effect by the column of hot air directly in the center of the coal basket rising and exiting the vents while a column of cooler air (less hot anyway) at the edges of the drum was falling and pulling in air through the gaps in the edges of the lid.

If you had a big slab of meat on it, there would be a heat sink and an obstruction in the airflow.

post #7 of 10
Thread Starter 
good points Dave, hadn't thought of that.
post #8 of 10
my guess is that your magnets are leaking. try a test. next time put a couple of strips of duct tape over the magnets to make sure they seal.

If the fire goes out, there's your answer. If it keeps burning, the only other place possible to get oxygen is the lid.

just curious, any other penetrations for bolts, etc. around the lower part of the drum?
post #9 of 10
I noticed the same situation on mine last time. Couldn't figure out why the !@##$# fire wouldn't go out! I checked and rechecked the intakes to make sure they were closed and not letting air in. Even took the lid back off and looked down into the drum to check for daylight slipping through the intakes. Nada. I'm not sure how many hours of confusion (why is this thing just sitting here and not cooling off??) passed until I realized that I hadn't put the screwed the fitting into the bung hole... Screwed it in, and temp started dropping within 15 minutes.

With the sun out here in OK, I have had cooks during the day where I've had to close all 4 intakes just to keep the temp down even close to where I want it...
post #10 of 10
I have found that I need to close the intakes and cover the exhaust. I had a flat lid with the holes and I always just covered the holes with cardboard and it went right out.

I now have installed a Weber lid and I just close the top vent.
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