Exhaust Help on Drum.....

[doctor phreak]

hey guys you all know i built my sooner drum well im in the process of seasoning it and i am having issues getting it past 325 with all 3 intakes fully open...in fact i went out there a minute ago and it was down to 165 temp i am thinking the exhaust is not big enough ...i have 4 - 3/4" inch holes the reason i think this is when i took the lid off the fire started going....it seems like its getting choked .....so question is should i add more holes to the lid maybe 2-4 more...whadda you think....heres a pic of the lid

[DDave]

Well, by way of comparison, here is a table for you.

One 2" hole (original drum lid bung) gives you 3.14 square inches of exhaust area

Eight 1/2" holes (somewhat popular pattern) give you 1.57 square inches of exhaust area

Four 7/8" holes (Weber lid) gives you 2.4 square inches of exhaust area

Four 3/4" holes (your lid) gives you 1.77 square inches of exhaust area

So your in the ballpark of exhaust for common configurations.

I am assuming the intakes are 3/4"??

I see that one of your intakes is elevated. I wonder if the riser is warm enough that air inside is trying to rise (since it is close enough to the drum to be heated) rather than falling which it needs to do if it is going to enter the drum? I would bet if you unscrewed your riser, you would get better intake flow.

Alternativelly, I would imagine adding a couple more exhaust holes would improve the draw and you could keep the riser.

I would also try again with known fresh charcoal so you know for sure it is not a fuel issue.

Hope this helps . . . some . . . I know it got kind of long winded.

Dave

[Fishawn]

Don't touch that thing!... Looks like a shiny Red Corvette!...lol... More holes? Or make the existing ones bigger and mount moveable covers that can swivel to partially cover said larger holes or outta the way to get it "wide open" with max exhaust flow?.. Just thinking out loud... Beauty Mike!

[Richtee]

I see that one of your intakes is elevated. I wonder if the riser is warm enough that air inside is trying to rise (since it is close enough to the drum to be heated) rather than falling which it needs to do if it is going to enter the drum? I would bet if you unscrewed your riser, you would get better intake flow.

Risers like that are not the ideal way to accomplish what you want. Flow characteristics in that pipe require that it be a much larger diameter-like twice- to get the same flow as no pipe. And I never thought of it heating up .

I am building a drum now, so I'm gonna experiment. But while I will try the "extended exhaust" control, it will be a rod extended up from a ball valve lever.

[ALX]

I have been seeing them on competition tour lately with 2 stacks(maybe 4 inch tall) about 6 inches apart on one side of lid as only exhaust....I know these folk cook higher heat(briskets etc.) on them......Wish i new enough about them...They maybe doing something different with intake a well....

Just throwing it out there..

[doctor phreak]

ok i took the riser off and have the ballvalve open 50% and both caps are on will let the fire mass settle down for 30-45 minutes and then see where we are at...i can already see a difference in temps they are now running pretty close together

[yt]http://www.youtube.com/watch?v=uW54WvCmjdo[/yt]

[doctor phreak]

Risers like that are not the ideal way to accomplish what you want. Flow characteristics in that pipe require that it be a much larger diameter-like twice- to get the same flow as no pipe. And I never thought of it heating up .

I am building a drum now, so I'm gonna experiment. But while I will try the "extended exhaust" control, it will be a rod extended up from a ball valve lever.

yea i will probably do this i have seen it done but i thought the riser i did would work ...well live and learn i go out and the next week or so and pu up a brass ball valve and a rod.....

[Richtee]

yea i will probably do this i have seen it done but i thought the riser i did would work ...well live and learn i go out and the next week or so and pu up a brass ball valve and a rod.....

Crap...I meant "intake" obviously...

Sounds like a winner Phreak! Merry Christmas!

[DDave]

ok i took the riser off and have the ballvalve open 50% and both caps are on will let the fire mass settle down for 30-45 minutes and then see where we are at...i can already see a difference in temps they are now running pretty close together

I have been seeing them on competition tour lately with 2 stacks(maybe 4 inch tall) about 6 inches apart on one side of lid as only exhaust....I know these folk cook higher heat(briskets etc.) on them

I wonder what diameter they are -- 2" maybe? I've thought about adding another daisy wheel vent to my Weber lid to give me more range. I have a hard time maintaining 350° when I want to do chicken. I can get it there initally but it seems to want to fall to about 325° when I put the lid on.

I have the bottom of the kettle that I could swipe one from but I'd rather have another top vent wheel if I can find one.

Crap...I meant "intake" obviously...

I figured you did.

Dave

[aczeller]

take this with a grain of salt... especially becuase I have never owned, built, operated, or even seen a UDS in person. lol

however, when we size things for HVAC equipment, ducts, etc, it all has to do with static pressures, hot/cold air tendencies, noice criteria, friction co-effients, air velocities, throws, etc... all in all, it all coes down to the fact that each situation needs to be sized approritely. one rule of thumb is that all equipment, duct, etc. needs and/or should be sized to about 125-150% of it's design requirements (as far as airflow goes).

what does this have to do with BBQ? this allows you to comfortably "cruise" at your desired temps, yet it also lets you "max it out" or "choke it down" for the exteme/rare situations that we all tend to find ourselves in sometimes.

with all that being said, I would probably upsize everything, then put dampers on the exhaust ports. probably go to 1" or 1 1/4" holes for the exaust, then just leave the intakes alone (since they are already purchased and installed).

Later,
Andy

[rbranstner]

My brother and I both have the risers on our drums and they run great. We have (4) 1" intake holes and the riser has a ball valve on it. Once the fire is going we are able to control the heat with just the ball valve. I will have to reread these posts to see if you gave this answer but how many intake valves do you have and what size are they?

[doctor phreak]

My brother and I both have the risers on our drums and they run great. We have (4) 1" intake holes and the riser has a ball valve on it. Once the fire is going we are able to control the heat with just the ball valve. I will have to reread these posts to see if you gave this answer but how many intake valves do you have and what size are they?

i have 3 - 3/4" intakes and now 8 - 3/4" exhaust....and it looks like i am still having trouble keeping temps it was doing great and fell down again so i may do the same as my last drum and drill 1 intake to 1" and then i have another lid and cut it out for a 2.5" x 6" stack....

[blues_n_cues]

speaking of drums,did bubba fall off the earth or what?

[doctor phreak]

My brother and I both have the risers on our drums and they run great. We have (4) 1" intake holes and the riser has a ball valve on it. Once the fire is going we are able to control the heat with just the ball valve. I will have to reread these posts to see if you gave this answer but how many intake valves do you have and what size are they?

can you also maybe post a pic of your drum...thanks

[DDave]

My brother and I both have the risers on our drums and they run great. We have (4) 1" intake holes and the riser has a ball valve on it.

Wow, that's more than double the potential intake air as (3) 3/4" intakes -- 3.14 square inches versus 1.32 square inches. More than one way to skin a cat. As long as you have more exhaust than intake for postive draft though.

speaking of drums,did bubba fall off the earth or what?

I think being the Lockharts BBQ pitmaster is keeping him pretty busy.

Dave