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-   -   Can a UDS air intake be too tall? (http://www.bbq-brethren.com/forum/showthread.php?t=35522)

JamesB 12-29-2007 08:32 PM

Can a UDS air intake be too tall?
 
On my UDS, I have two 1" openings. I placed one (the only one I thought I would need) on a 1" pipe with the ball valve on top and the other just capped off on the side of the barrel at the bottom... Had trouble maintaining temp the first couple of cooks. Did OK, but I just thought that it was a learning curve that I needed to get over... Anyway, I have noticed that adjustments made to the intake on the pipe provides very little if any change. After adding a ball valve on the bottom intake, I make all adjustments there with great success... So what is wrong with my 'no bend over" intake? Too tall?

Since these pics, I have added two more exhaust vents to the lid just to see if that made any difference...

Here is a reminder of that my UDS looks like...
http://bennett-family.com/pics/pits/...s/uds_side.jpg
http://bennett-family.com/pics/pits/james/uds/uds.jpg

sampson 12-29-2007 08:47 PM

It looks like you could disconnect the long pipe fairly easily and test it with the ball valve just connected to the nipple coming out. I'd be real interested in the answer to this one as I just bought the pipe today to make all four of the intakes that I am doing on a new drum. I bought 24" nipples to do this with. I'm not sure that the total exhaust on the two pipes you have going is enough, on the one that I do have up and running, there are 8 half inch holes to vent...

JamesB 12-29-2007 08:54 PM

Since that pic was taken, I have added two additional 1" exhaust ports for a total of 4. No net effect from that. I tried to disconnect the pipe prior to my beef rib cook tonight, but it would not easily come off and I didn't want to go get the tools.. I will be removing the upright pipe to see what effect it has.

thx,
James.

Bbq Bubba 12-29-2007 09:03 PM

As i do not yet have my UDS completed, from my research, i'm thinking the tall intake would be great but your pipe is to small....
I'm thinking 1 1/2 or 2" at least??
The pro's will be along shortly :cool:

Browser 12-29-2007 09:20 PM

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?

JamesB 12-29-2007 09:23 PM

Quote:

Originally Posted by Browser (Post 524870)
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?


That's an interesting concept...

smooookin 12-29-2007 09:26 PM

From looking at the pic the first thing that came to my mind is you need an elbow at the top of the intake. My thinking is the air isn't going to just jump into the hole. With an elbow you would be forcing the air down the pipe.

JamesB 12-29-2007 10:05 PM

Quote:

Originally Posted by smooookin (Post 524874)
From looking at the pic the first thing that came to my mind is you need an elbow at the top of the intake. My thinking is the air isn't going to just jump into the hole. With an elbow you would be forcing the air down the pipe.

Well then, does it just stumble into the other inlet on the other side of the barrel on the bottom??? :lol:

Seriously, the thought process here was that once I apply lit coals, they would heat up the drum and as the hot air rises, it would provide a convection air current to pull the intake air through the pipe. It's been done here before with apparent success but I have not seen one that extended above the barrel. Oddly enough, I can control the temp with the 1" intake that is near the bottom... open or close the one on the pipe and no effect (and yes, it is not clogged, I checked!8)) The barrel works well, but I want to be lazy and use the pipe...

The next burn I will remove the pipe and see what effect that has...

Thanks and keep the ideas coming!
James.

smooookin 12-29-2007 10:15 PM

so when you remove the pipe will the intake be vertical or horizontal? I think you are asking a lot of that size pipe, the reason for the elbow would be sort of a "ram air" effect. Just my line of thought since even a breeze doesnt blow down.

JamesB 12-29-2007 10:17 PM

I get what your saying. I will remove the pipe and the elbow when I give it another go... That way both of the intakes will be horizontal.

Thx,
James.

yelonutz 12-29-2007 10:42 PM

Have you considered that your intake runs right next to the barrel all the way up? The opening is right next to the coals. I think that with the hot air rising, air is trying to rise up the intake and slowing down the incoming air. The nipple at the bottom, other side is 90 deg to the rising air flow so would not have air rising or coming out of it. How hot does the pipe get. I think I would try removing the pipe, install the valve on the nipple and them attach a 4 foot (more or less) rod down to the valve. Put a handle on top of the rod. That way you could adjust the air flow while standing up and not have a "venturi" effect. Nutz

JamesB 12-29-2007 11:40 PM

The pipe stays cool to the touch. I'm leaning towards abandoning the pipe all together...

James.

keale 12-29-2007 11:47 PM

I have two 3/4 in. pipe nipples, and 2 ~3/4 in. vertical pipes. one w/ ball valve. One with an elbow... This past cook, I actually blew air down the pipes with a pump, for some reason it does (at least for mine) inhibit air flow. The pipe nipples, because its short, more air definitely goes in. I proved this on MY UDS by closing all vents- opening 1 pipe intake, let UDS run...then closed all vents and used 1 PIPE NIPPLE air intake, temps rose about 20 degrees higher.
Anyways, thats MHO!!

N8man 12-30-2007 06:02 AM

Physical Science In Action!!!!
 
I think your intake pipe is too long in relation to your exhausts height. In the convection loop, air flow tends to follow the path of least resistance, so when you ran with the bottom intake open, you saw better response in the air flow, or air draw, as opposed to the vertical intake. On my DrumPit I have the one vertical pipe, 1" dia., choked on most of my smoking sessions to about half of the opening of the pipe diameter and I maintain temps around 225*-250* consistantly. My exhaust is a single 2" pipe that I position opposite the air intake. I don't think the elbows I have on it make any difference in the flow.
My intake pipe height is below that of my exhaust pipe height and that may
aide in the convection processes. I hope my rambling helps!!!!
http://www.bbq-brethren.com/forum/at...4&d=1198592409

chinesebob 12-30-2007 06:08 AM

Quote:

Originally Posted by N8man (Post 524998)


Off topic but N8man - how did you build yours on to the wheels like that?


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