Can a UDS air intake be too tall?

Was lookin for this thread... when i built mine i thought taller intakes would be better. Im running 1/2" intakes 4 of them. 2 with the vertical pipe/ballvalve/90* on the end. Well was planning on cookin 2 spatchcocked chickens this after noon started my fire about 330, couldnt get it past 250* which i guess was good for brisket etc. but i wanted to take it higher. I started out with about half a chimney of lit coals to a minion method. I just dump lit coals all over the top( no can method) I got to reading and decided to take the long pipes out and just run the ball valves on the sides. soon as i did that and let it sit for a few min temps started climbing. well i decided to fire up the kettle for the chickens, but i bought a chuckie as well so im throwing it on the drum. But i can attest that having the intakes higher than the exhaust will definitely make controlling temp harder. its running at 245-255 now still tryin to get it dialed in. have 1 nipple open and 1 valve half way.
 
I can see where having the intake higher than the exhaust can cause a problem as in it not knowing where to pull clean air from and causing it to 'vapor lock' if you will.
 
JamesB said:
That's an interesting concept...
Click to expand...
I am thinking browser has a good point. When I first saw your UDS, I wandered if the tall intake would act in reverse of a ciphon and try to pull the air in from the lid. I think you already have plenty of intake and exhaust..or at least close. Mine all work fine with weber lids which only have 4 - 1/2 exhausts. Just my $.02.
 
I should have read Browsers post.
 
yea.. still havin issues of temps fluctuating but i think it is due to the learning curve. I have 1 intake open now and valve 3/4 open, it had climbed from 235 to 250 or so... will play with it through out the evening and see what i can get it to stabilize at. im thinking i need 8 little flat magnets to put over the exhaust holes when i close it down at night. other wise im loosing a lot of charcoal lettin it burn down every time.
 
My UDS knowledge has grown from my first post on this thread...
I now have 2 drum's, 1 with 3/4" intakes and cap's w/ 1 ball valve down low and now 1 with a riser, have used them both in similiar weather condition's, not playing know it all but have done my homework!!!

Model with riser is much harder to lock in temp, don't know if it's the volume of air IN the pipe that has to stabilize or the height issue with it reverse flowing but it IS a different beast, actually saw smoke EXITING the intake on several condition's!!
It finally did settle down at 228* after some fidgiting and stayed for several hour's but seemed to burn thru the coal twice as fast! 8# only lasted 10 hr's...:confused:

First drum is 1 cap off, valve open about 1/3 and run all day at 235, no question's asked, plus i have done a high temp chicken cook at 325 with great success.....:wink:

Just my opinion having used both system's....
Btw, i have a 2" exhaust on both lid's....work's GREAT!!! :biggrin:
 
Bubba, seems like a lot of brethren have a 2" exhaust that works very well. Whatever intake is used seems to work with that setup since the temp is regulated by the intakes. KEEP IT SIMPLE!!! Just thinking outloud and getting ready to mix up an adult bev.:biggrin:
 
Simple equation, simple answer. Path of least resistance. The fire will draw air from exhaust if it is easier, especially if larger diameter.
 
Norcoredneck said:
Simple equation, simple answer. Path of least resistance. The fire will draw air from exhaust if it is easier, especially if larger diameter.
Click to expand...


i ditched my 2" exhause as i found it hard to control temps with a 1" intake pipe. as soon as i did that, and drilled the holes into the lid, the drum holds temp better.

I truly think that using 3-4 intakes at the bottom works best. if you dont want to bend over to adjust the valve, just use your foot. my valve isnt the rotating type so i know how much its open or closed
 
There is always ways to make improvements. Also, don't fix it if it ain't broke. This forum always offers new idea...which is great!...but goes back to the basic UDS design, which is simple. Always look forward to new ways to tweek the UDS. Thanks to all the ideas.
 
Browser said:
I don't s'pose it'd be anything like the height of the intake means the air is trying to get in via the shortest path i.e. one of the vents rather than the intake pipe?
Click to expand...

The hot air is going to exit the ports on the lid...hot air rises.
This will create negative pressure inside the drum and draw air from you intake in.
 
Well after reading this thread ... think I need to enlarge my exhaust. I have 4 3/4" intakes and a 1 1/4" exhaust. On my last smoke..I fought the temps. ... seems 2" exhaust is the norm ... would think all the holes in the lid equal 2".
 
gotwood said:
The hot air is going to exit the ports on the lid...hot air rises.
This will create negative pressure inside the drum and draw air from you intake in.
Click to expand...

Actually the tall intake may partially act in a chimney effect trying to draw the hot air up also. It may not actually exhasut, but the effect may be rather balanced and create a standstill in the intake riser.

To better understand this, if you cover the exhaust vents and open boththe the lower and upper intakes, I'm sure you would find that your higher intake would definitely now act as an exhaust port.
 
I haven't built a UDS, but here's something for you from left field.
When I was taking S.C.U.B.A. courses, we learned about snorkel design.
The one thing that sticks out, is that if you increased the length of the snorkel, you also had to increase the diameter of the snorkel to get the same airflow.
So, if you have a longer air intake on your UDS, you will also need to have a larger diameter pipe to facilitate the same airflow.
I also am thinking about when using my offset, I'm pretty sure that my exhaust opening is typically about 2-3 times the size as my intake opening. The cool air that is coming into to your cooker is going to expand a lot when it gets burned and gets hot. You need to have a bigger place for that air to go out than come in.
 
i think you are wasting your money my (4)1" pipes down at the bottom with 1 ball valve works fine those smoke stack things look good though
 
Harbormaster said:
I haven't built a UDS, but here's something for you from left field.
When I was taking S.C.U.B.A. courses, we learned about snorkel design.
The one thing that sticks out, is that if you increased the length of the snorkel, you also had to increase the diameter of the snorkel to get the same airflow.
So, if you have a longer air intake on your UDS, you will also need to have a larger diameter pipe to facilitate the same airflow.
I also am thinking about when using my offset, I'm pretty sure that my exhaust opening is typically about 2-3 times the size as my intake opening. The cool air that is coming into to your cooker is going to expand a lot when it gets burned and gets hot. You need to have a bigger place for that air to go out than come in.
Click to expand...
I was going to say the same thing... If you want to have a long intake, you need to increase the size of the pipe you use...
 
Yes; at some point FAA regulations kick in. (smartass mode)

I know it seems to be a tradition using steel pipes & brass ball valves and such for intake & exhaust, but that's all unnecessary. There are simpler and cheaper ways to control air flow. And nothing to stub your toe on. You can easily duplicate what Weber uses on its kettle tops. It works on the bottom too for inlet air.
 
I know everybody wants to get it right the first time but what is kind of neat about the UDS is how everybody makes it their own. Don't be afraid to try new stuff and when it works be sure to brag about it.

All the talk about intake pipe lenght got me out to my barrel tonight. I loaded it up and let it run wide open. It got up close to 330. I then ground the welds off and replaced my intake pipe with an 18" pipe shoved in 12"(same as original pipe). After 1/2hr the temp had climbed a few degrees but never over335. I put my original pipe back in and after a while the temp was running 331 to 332 pretty steady.
It appears on my barrel that the slightly constricted bend and 30" of pipe have little effect on the intake.
 
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