Another 120 Gallon Compressor Tank RF Build. Appreciate any help.

Discussion in 'Reverse Flow' started by storeman0913, Feb 2, 2015.

  1. Will post some pictures later today but am gathering materials for building a RF from a 24" x 69" 120 gallon old air tank.  It is 3/16" thick, minus whatever rust I find when the door is cut out.  This will be ground mounted on casters or wheels.  The support frame came from the integral aluminum frame of a Navy carrier ship's desk which was never installed.  Feet on the desk frame are steel explosion welded to aluminum, so I'll use the frame upside down so the feet can be welded to the tank.  More to come later today. This is my first smoker build and my first real welding project.  Lots of welding equipment, limited skills/knowledge.

    Last edited: Feb 21, 2015
  2. Jerry

    It sounds like it is going to be a nice smoker. I look forward to watching the build.

    Happy smoken.

  3. Thanks David,

    Here are some shots of the tank and frame at it is now.  With construction going on around our house, I can't get it to concrete for a solid work surface for a while.


    With the pipe screwed in I can manipulate the tankand is gives a point to attach a come-a-long to pull it back up hill on the tilted frame.

    Legs at the firebox end with overhang removed (aluminum fillet weld and 1/2" of the explosive welded plate)  to allow the firebox to be bolted to the 3/8" thick aluminum frame.

    This design is similar to my target

    Need to buy 1/4" steel plate for firebox and plenum.  Also need to buy 3/4" #9 expanded metal.  The rest of the materials I pretty much have in my collected scrap.

  4. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    On another thread you were having questions about the exh. stack size....   5" ID about 36" tall will work...  If  you use the 3" ID pipe, you will need 4 stacks about 36" tall, and those 3" stacks will have a friction problem...
  5. Dave,

    If two  3" pipes (14 sq") more than  equate to about one 4"  (12.5 sq" ), why does it take four 3" pipes to equate to one 5" (19.6 sq")  ?  I don't understand.

  6. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Because of the surface area ratio to volume.......   WAY MORE surface area and that equals FRICTION.....  friction screws up a natural draft smoker....
  7. Thanks Dave.  I'm having trouble finding 5" pipe but am continuing to search.  Is there a problem going oversize for a stack, for example 6" ??

  8. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    6" will be fine...  same height...  If it draw too much, a choke plate on top of the stack will fix that....    Better too big than too small.....

    A choke plate could look like a steel plate with a 5" hole cut in it and placed on top of the stack...
  9. Thanks again Dave,
  10. Nice,

  11. Have mounted wheels to the frame and cut the door out and welded edge strips to it.   My welding instructor from the 2 intro classes I took this Spring would be embassassed at my results, as am I...but it won't fall apart!   Also cut the opening for the fire box and spent a couple of hours with a right angle grinder with wire brush removing interior rust as best I could.  Sorry I haven't taken any pictures.  With the weather, I've moved all this into my 12' x 12" "welding room"  (that is a stretch as pictures will show).  Will take some this weekend.

    I just ordered steel. Am going to have the yard shear the 4' x 10' steel plate to fire box piece dimensions and RF plate size.  For the $65 shear fee, I figure it will save me a ton of work and consumables.  Got the new sheet of 1/4" 4x10' for $225, about 55 cents a lb. .  Happy about that since the scrap yard wanted 50 cents a lb. for the same rusted item.  Couldn't find 5" pipe at scrap yard but managed to get a 66" drop of schedule 40 from my steel supplier.  Not cheap at $66.00.  4x8' sheet of #9 flat expanded was $60....pleasant surprise.  Materials should arrive early next week. 

    I figured there wouldn't be any harm in making the opening at the end of the RF plate a bit larger so I did so.  Fire box intrudes about 7" into the tank.  I plan to leave 9" at the far end but can change that if advisable.  Seems to be in line with "less friction".   Meanwhile am fashioning hinges from 1/2" black iron pipe (inside diameter closer to 19/32") and some 9/16" copper ground rod I had in scrap (self-lubricating hinge pins).  Pictures promised.

    Last edited: Feb 20, 2015
  12. citislicker

    citislicker Newbie

    Jerry, thank you for the thread

    You know, I have never used a welder in my life, and was thinking of building a reverse flow smoker myself. I know it would be built better than the store brands. 

    Inspiring post. 

  13. Thanks Citislicker.
    citislicker likes this.
  14. citislicker

    citislicker Newbie

    "I like to see more pics on your build and how you cut that bottom part to attach the fire box.,"
  15. Me too  Pictures are good 

  16. Question for the experts....Since I will have surplus 5" pipe from the 66" drop I'm buying, I'm wondering if I could use some of the 5" pipe on the fire box for oversize vents for both the low vents to control the fire and above for the vent to control heat distribution,  My idea is that I can always choke the vents to the required smoking temps but oversize vents might offer the opportunity to create a convection oven effect which could allow quick cooking of burgers, steaks, etc that could be done at 400-500 degrees.  Trying to get double duty out of this unit since my wife is not a smoked meat fan, but I am, as are several friends.

    We host a military retiree picnic each year which involves about 75 folks.  The attendees pay $5 each and bring a dish.  That $ allows for burgers, dogs, some chicken and buns and condiments.  Can't see a way to sneak a big smoke in the budget.  We always have to borrow the Rotary Club's big gas grill for the event.  Trying to make this beauty serve that purpose as well as my desire to smoke.

    What do y'all think?  Need feedback from those who know.  I'm betting I'm not the first person with this notion.

    Last edited: Feb 21, 2015
  17. Apparently no opinions on my notion of combo smoker/cooker?  I'm surprised.

  18. Post a sketch so we can better understand what you are wanting to do 

  19. I'll try as I have time but I'm no good at sketching.  That is why I tried to spell it out above.  Bottom line is way oversize firebox vents.  Will they give me a high heat cooker (and when tuned down) a smoker?

  20. Promised some pictures this weekend.  Between frozen pipes and helping a neighbor with his, I'm whipped.  Here are some pictures as promised.  Tank is sitting free on frame so I can move around as needed.   At 71 years old, my butt is dragging.  Good night.




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