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Q-talk *ON TOPIC ONLY* QUALITY ON TOPIC discussion of Backyard BBQ, grilling, Equipment and just outdoor cookin' in general, hints, tips, tricks & techniques, success, failures... but stay on topic. And watch for that hijacking.


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Unread 06-16-2010, 10:45 AM   #1
mjancel
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Default reverse flow

i have no clue what reverse flow is. can someone describe how it works and maybe a drawing. thanks
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Unread 06-16-2010, 10:50 AM   #2
Lake Dogs
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www.pigroast.com or www.bubbagrills.net The smoke stack is on the end by the
fire box. There's a baffle that goes the entire length of the smoker with an opening at
the end opposite the firebox. This makes the heat and smoke travel the length of the
smoker, then is allowed up into the cooking chamber so as to travel back (reverse)
towards the smoke stack. They provide a more even heat and more even smoke,
IMHO.
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Unread 06-16-2010, 11:03 AM   #3
Konrad_Haskins
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Pictures of all my reverse flow pits are on my BBQHog website. I've own(ed) three my first was fabricated by my now ex-brother in law, now sold My second 48-Dlx and third 60-Original are Lang's sitting on the same trailer. I also used a buddies 84 to take RGC and beat iQue a couple weeks back. I like reverse flow and I like what Ben Lang does. His third generation pits are cold rolled from 1/4" steel. They also have a second heat baffle for the first 18" from the firebox. There is a little variance and a biscuit test is still called for. For me what Ben does is better than a propane tank. Although at the end of the day it's the pitmaster not the pit.

Hope that help,
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Unread 06-19-2010, 05:59 PM   #4
mjancel
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thank you for your help
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Unread 06-19-2010, 07:03 PM   #5
el_matt
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Quote:
Originally Posted by Konrad_Haskins View Post
Pictures of all my reverse flow pits are on my BBQHog website. I've own(ed) three my first was fabricated by my now ex-brother in law, now sold My second 48-Dlx and third 60-Original are Lang's sitting on the same trailer. I also used a buddies 84 to take RGC and beat iQue a couple weeks back. I like reverse flow and I like what Ben Lang does. His third generation pits are cold rolled from 1/4" steel. They also have a second heat baffle for the first 18" from the firebox. There is a little variance and a biscuit test is still called for. For me what Ben does is better than a propane tank. Although at the end of the day it's the pitmaster not the pit.

Hope that help,
The second baffle, is it just lower, like a heat shield? Is it an enclosed "box" that is insulated?

I like the concept of reverse flows, but have wondered about the heat from the fire-box side.

Matt
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Unread 06-19-2010, 07:46 PM   #6
jestridge
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In other word the heat is traveling farther getting the max. usage out of every btu
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Unread 08-30-2010, 03:10 PM   #7
SQWIB
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Quote:
Originally Posted by Konrad_Haskins View Post
They also have a second heat baffle for the first 18" from the firebox. There is a little variance and a biscuit test is still called for. For me what Ben does is better than a propane tank. Although at the end of the day it's the pitmaster not the pit.

Hope that help,
Konrad would you have any pics or drawings of this?
I am having trouble with my build, usually averaging 70 degree difference from one end to the other


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Unread 08-30-2010, 03:21 PM   #8
Dave Russell
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No expert here, but I'm guessing you're getting a lot of radiant heat due to the small diameter of the tank, and maybe not enough draft. Like I said, no expert, but the ones I've seen were larger diameter, putting more space between the firebox and the meat.

Can you shield the fb end better or provide better draft and circulation?
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Unread 08-30-2010, 07:42 PM   #9
JayBirde
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@SQWIB:
I believe the opening from the firebox to the pit is too small, causing draft problems. There is a formula that needs to be used to get the firebox to pit opening size, the gap at the end of your smoke shelf and the diameter and length of the stack. Increasing the length of your stack will increase your draft.

My reverse flow has a 10 degree difference from one side to the other, but is also a LOT bigger.

PM me and I will see if I still have that spreadsheet with the calculations on it.

Nice looking build, though!
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Unread 08-31-2010, 07:22 AM   #10
SQWIB
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I followed the Pit calculations.
The opening into the fire box is actualy slightly larger than needed.
I agree its radiant heat but felt I was getting a good draft.
The stack is 2" higher than the pit calculations suggest.
The stack however only rest 2" inside the chamber, it does not go to grate level.
here is a blog to the build.



and here are my calculations.




thanks for taking the time to help and sorry about hijacking the thread
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Unread 08-31-2010, 08:45 AM   #11
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Oh, OK. Opening just looked really small in picture and couldn't see top of stack. That is the same spreadsheet I was gonna send you, but I don't think you will need it now! I will have to measure my smoke shelf, because I can't remember if I put a pitch on it or not. Weird that you are getting that much of a temperature difference!
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Unread 08-31-2010, 09:30 AM   #12
SQWIB
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I think its mainly radiant heat, note the picture, whats circled in red is how muck the top of the firebox is in the smoke chamber.
I think I am gonna put a baffle in 2 parts, 1 inside past the firebox and 1 inside the fire box under the first baffle.




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Unread 10-04-2010, 11:18 AM   #13
SQWIB
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Temp Variance Update

Here's an update posted on my website.


WEBSITE


Update 9/01/10.

I was a bit unhappy with the most recent cook, I was getting an average of 70 degree difference from left to right, sometimes peaking to a 90 degree difference, this was unacceptable. I did not realize the difference was so great until my cook last weekend.
I tried Fire management and that had no effect.

The top of the firebox was getting hammered with heat and 6" of the firebox is inside the smoke chamber.
There is definitely a lot of convection going on.

Here is how I fixed the problem.
The Green represents the top of the firebox that is inside the smoke chamber, the Blue represents the reverse flow plate and the Red represents the baffle plates installed to reduce the heat from hammering the top of the firebox, causing excessive radiant heat.

CLICK ON THE ABOVE DRAWING FOR THE TEMPERATURE TEST RESULTS

Now I am getting an average 23 degree difference. I most likely could get it closer, but like the idea of being able to my ribs and butts together, I usually do ribs at 215-225 and Butts at 240-250





Last cook I was averaging 15 degree variation in temps, Heat recovery is about 3 minutes if the smoke chamber lid is opened more than 15 seconds. Its almost immediate if opened under a minute.

TEMP TEST 2 LINK

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Last edited by SQWIB; 10-04-2010 at 11:55 AM..
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Unread 10-04-2010, 03:36 PM   #14
ChuckC
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So I just started my reverse flow build and I had a question about the convection and temp variances.

Did you ever consider remotely mounting the firebox? My plans were to mount the firebox as you did but during last night's bout with insomnia, I had the idea to mount the firebox slightly apart from the cooking chamber using square or rectangle tubing as a vent which would also run the length of the chamber and venting on the far side, thus creating the RF design.

Last edited by ChuckC; 10-04-2010 at 09:13 PM..
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Unread 10-05-2010, 06:52 AM   #15
SQWIB
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Quote:
Originally Posted by ChuckC View Post
So I just started my reverse flow build and I had a question about the convection and temp variances.

Did you ever consider remotely mounting the firebox? My plans were to mount the firebox as you did but during last night's bout with insomnia, I had the idea to mount the firebox slightly apart from the cooking chamber using square or rectangle tubing as a vent which would also run the length of the chamber and venting on the far side, thus creating the RF design.
I think that's a good idea but would leave more room in case you wanted to run another baffle under the reverse flow like a c channel, to move that heat quickly to the center or other end of the smoker.

I have looked at a ton of designs and someone drew one up like that and thought it would work.

I would do all your temp testing before finishing the smoker in case it doesn't perform as you would like.
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