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"Say It Ain't So", Another 120 Gallon Build ?

post #1 of 22
Thread Starter 
Yup... It's true ...

So I got this tank (120 Gallon) ... Started researching 120 builds .. found this one, http://www.smokingmeatforums.com/t/144914/120-gal-rf-build-first-build-advise-welcome#post_1306676 and read it (again) .. His is pretty close to the same size as mine... 24" diameter .. 54" between welds... 67" overall (w/round end caps)... Was looking at Dave's drawings for sizes but it's of a different size tank ... So I ran a few numbers in the calculator and came up with these....

[url=http://feldoncentral.com/bbqcalculator.htmlcc= 0,0,120,0,0,0,27720.00,9240.00&fb=24,24,24,0,0,13824.00,9240.00,149.6&
ch=6,691.20,24.46&fi=4,2.75,0,41.47,3.77&fc=11.87,16.78,110.59]Link to BBQ Pit Calculator[/url]

As RJ said on the other build... If I try to punch in dimensions of the tank... I get different results ... I'm not the best on figuring out them thar gadgets (Feldon's calculator, circle calculator) ... If there is something I didn't do right, please let me know...

Edited by JckDanls 07 - 1/30/15 at 6:04pm
post #2 of 22

Use this calculating helper....




post #3 of 22
Thread Starter 
OK.. so after an hour or so playing with all these calculator's... my head's spinning... I'm dizzy... don't know whether I'm coming or going... but then again.. I'm only playing with roundabout numbers for now... don't know the EXACT measurements as I haven't cut into the tank yet to determine metal thickness... I'm assuming it's 3/16 as that is what the legs are.. the tank was an air compressor.. the tag says it's a 120 gallon tank...
post #4 of 22
Thread Starter 
playing with numbers some more... I can't seem to get Feldon's to match up with Dave's numbers ... just using the volume on Feldon's calculator...
post #5 of 22

You won't   Dave.s is better than feldons    For RF's



post #6 of 22

^ Yes the above is correct. Feldon's is OK for offset but needs to be 1.5 times the area under the RF plate and CC to FB opening for reverse flow. Those numbers will match up with what Dave put together.

post #7 of 22

Did you read all the dialog ??????     There is a reason the two calculations don't match up.....




Smoker Calculator reasoning
The concept for the changes is below.... Alien and his associates, did an amazing job putting the original calculator together... 100% of my numbers are based on his original numbers... small changes were made for the improvements due to design changes in smokers.....
The original measurements were taken from SFB smokers with tuning plates I do believe.... The advent of the RF smoker did not make any changes to the calculator... Now the exhaust has to travel twice as far as before, and the original FB/CC opening restricted the air flow from the FB, causing the FB to over heat... Some would get up to 450 deg and higher while the CC wouldn't get over 250.... And then there is the increased friction from the steel.... When using natural draft, any restriction/friction is very detrimental to the flow....
So, on a whim, the FB/CC opening was enlarged, the area under the RF plate was increased and the area at the end of the RF plate was increased... all by 50%.... That solved ALL the problems.... fuel consumption was reduced.... folks were happy....
I personally experienced members improvements and fuel usage by the letters/PMs they wrote me on their improvements...... One additional modification was suggested.... members here, tested a second air inlet to the FB.... directly across from the FB/CC opening... That was a significant improvement of some/most smokers.... If the FB was too hot, it could be cooled by opening the upper air inlet.... Also, the fire had a separate air inlet to adjust it's heat output.... It should be installed at or below the wood fire grate....
All of this has been tested and proven by members building smoker on this forum.... The only place you will find using these numbers... or it used to be... I'm sure many builders are now using these ideas for their builds.... this process has been going for at least 2 years....

Thanks for all your help...... DaveOmak

post #8 of 22
Thread Starter 
problem I was having with Dave's is... my length ... I have rounded ends on the tank... the volume of CC should at least match between the two.. no ?? so do you use the overall length ?? ... between welds ?? .. kept playing with different lengths trying to get them to match...

post #9 of 22

The problem with using the "volume" tag on the tank is........   when it is a propane tank, the tank, by law, can only be filled to 80% to allow for expansion....  some tags have water volume and some just have a propane volume.... 


And the minute/small difference in the rounded end caps is insignificant....   don't mean squat.....   


How do you know Feldon's has the right numbers ?????   How do you know our calculator is wrong  ??????   


Take your pick....  

post #10 of 22
Thread Starter 
Dave... you got it all wrong... not saying one or the other is right or wrong .. was just thinking the 2 volumes would have been the same... So do I use the overall length then in your calculator ??
post #11 of 22

Take an average length.....   pick a point between full length and where the tank has straight walls...

If the domed end is ~about 8" long, subtract 8" from the overall length because there are 2 domed ends...  1/2 of each would be 8" total... 

OR, use the tag gallons, if it is in water, and multiply by 231....  231 cu. in. in a gallon....

Sorry about the reply, I DID misunderstand....   I reread the posts and I  misinterpreted what was said...     Dave

post #12 of 22

post #13 of 22

I like smoker builds, I've built a few myself  be watching



post #14 of 22

Watching! Can't wait to see it come together Keith! 

post #15 of 22
Thread Starter 
The tag on the tank is rusted right where it says gallons.. I assume it is water gallons since it is an air tank.. I can read it enough that it says 120 ...

Dave using your calculator there is no mention of firebox size... would I just use the recommended firebox size on Feldons to the volume calculated with your numbers ?? .. came up with 22" x 22" x 22"

numbers calculated came out to be ... tank is 24" dia. X 67"L (54" between welds) I used 61" as average ...

  • Volume = 27595.8144 sq in. , 119.4624 gallons
  • FB/CC opening = 110.383 sq in.
  • Area under RF plate = 110.383 sq in.
  • End of RF plate = 110.383 sq in.
  • Intake vents = 27.596 sq in.
  • Exhaust volume = 469.129 sq in.
  • Stack height = 23,892 in. (this is with 5" dia. pipe) I have access to ether 5" or 6"... 4" comes out to 37.333 in.. I will have to see if I can find this dia. pipe as I understand 36" +/- is ideal..
Coming up with 5 (3 under the fire grate and 2 across from CC) - 2" x 3.25" intake vents ...

Onto the circle calculator... using 12" radius
  • Segment Height ED - 7"
  • Chord AB - 21.817"
  • Segment Area - 109.76"

I'm sure there is something I am missing... Please correct my numbers If I am wrong ....
post #16 of 22

 Dave using your calculator there is no mention of firebox size.......     



There is now !!!!!!!!!    Thanks much......    You win the prize.....   Oreos and cold milk....




post #17 of 22

Volume in cubic inches X 0.017 = Exhaust Stack Volume in cubic inches, above the CC.... (ESV)

Exhaust Calculation..

ESV in cubic inches___469_____________________ ... = Stack Length in inches (36" +/-) 37.3" tall   Use 5" 36" tall
0.7854 X 4" Stack Diameter X 4" Stack Diameter

Adjust the diameter of the stack, until the proper length is achieved... be sure to measure the actual internal diameter of the pipe used..
this is for round stacks only..



The taller, bigger dia. stack is not a problem.....  smaller and shorter would be a problem....   natural draft smokers are "touchy" when it comes to restrictions but not when they are allowed to breathe....

post #18 of 22
Thread Starter 
Originally Posted by DaveOmak View Post

 Dave using your calculator there is no mention of firebox size.......     

There is now !!!!!!!!!    Thanks much......    You win the prize.....   Oreos and cold milk....


LOL.. How did you know that's my favorite... My frozen beer mug gets used more for milk than it does beer ...

I spotted some 4" pipe today... going to put a piece of each size on and see which one looks more ascetically pleasing... So do my numbers look like they are going to work ?? want to get started burning myself... eerrrr, I meant start burning some steel ...
post #19 of 22

Looks good to me....  I've been putting crushed ice in my milk....     Dave

post #20 of 22

I like Ice Milk



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