Can a UDS air intake be too tall?

[JamesB]

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...

 

[sampson]

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]

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]

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

 

[Browser]

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]

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]

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]

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]

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]

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]

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]

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

James.

 

[keale]

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]

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!!!!

 

[chinesebob]

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

 

[N8man]

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

Try this: http://www.bbq-brethren.com/forum/showpost.php?p=506013&postcount=124

 

[JamesB]

Thanks every1 for all the ideas. I will let ya know how the next cook goes... I'm going to try a shorter pipe and then no pipe for comparison...

James.

 

[wlh3]

Here is my Drum> I have a 2" inlet pipe and a 3" exhaust thats all. The only thing I did different after the first few cooks was use my lid band. This helped my Temp control alot. I can now pretty much dial in the temp I want and it stays there. I think once you go to a shorter air inlet pipe and try the lid band temp control could improve for you:biggrin:

 

[JW]

James B it is best that the air intake does not extend above the height of the barrel, also your exhaust needs to be at least 1/2 inch larger in diameter than the air intake, this will help with creating a draft. WLH3 used a design that I have been using for a couple of years now with rather good success. I just made one for my dad and during the seasoning process he was amazed at how much air he could feel being pulled into the air inlet tube. Look for some of my post in the UDS thread around page 18 - 19 and check out what WLH3 has done with his barrel, I find that keeping the inlet about 2 inches below the top rim of the barrel with a single large exhaust gives the best results.

Minimum recommended tubing sizes: 2" inlet with a 2 1/2" exhaust.

Hope you get it going soon.

 

[CritterCook]

I have had great luck keeping temp with mine. I'm a newbie with these but maybe with larger exhaust it might draw harder.