Reverse flow questions...

[Mmmmm]

I'm going ahead with the pressure tank smoker idea, but I have a few questions about first of all the pit calculator and also about the reverse flow in general. I am hoping to start on this tomorrow if possible but I need some input.

Regarding the pit calculator: I live at an elevation of nearly 4000'. I don't know if it's my elevation or the super dry climate, but ALL of my cookers require more air than 99% of what I read about online among grilling / bbq forums. It is especially noticeable in my BGE and my drums. Most guys get by with 3/4" valves in their UDS's, and I have to use 1" or I can't keep them hot. My Egg as well, some people post their vent settings for a specific temp and I have to run a lot more air to achieve that temp. That being said, should I build the fire box 10% oversized according to the pit calc? Also, should I build the air intake vents oversized as well? I suppose that really doesn't make any difference if that's too big or not, I'll probably just oversize the intake regardless since I can just close it down if not needed. My main question would be the fire box.

The next question: RF or simple offset with tuning plates. As you all know the tank is fairly thin wall (haven't cut into it yet so I'm not sure how thin). With a thin tank is a reverse flow going to be a negative, meaning that if the heat/smoke has to make two trips the length of the CC to reach the chimney will the heat loss be too great and I won't be able to keep it hot? Would an offset with tuning plates be a better design for this tank? Or doesn't it make any difference?

Lastly, I am interested in a warming cabinet or a vertical section on the end of the main CC. I have a second tank, the air compressor tank I mentioned in an earlier thread. If I make an offset I might weld that tank vertically off the chimney end of the cooker. If I make a RF I might weld it vertically on top of the fire box. If I do either of these scenarios, do I need to upsize my fire box? Also, if I welded it above the fire box, do I need an adjustable opening in the top of the fire box, or is radiant heat from the fire enough to keep it warm? Or, do I pipe the exhaust through that section and place a chimney in the top of the vertical section?

I really like the idea of the RF but if this tank isn't well suited for it I'll go with an offset. I just have quite a few questions I'd like you fine fella's to chime in on. I need to get this stuff nailed down asap because I was hoping I could have a buddy with a plasma table cut the plates for the FB and intake vents tomorrow if possible but I gotta get him some drawings.

[Big T]

I would go 115% on the FB and you can make the intakes larger as well. I'm not sure how thick those tanks are but there are a few of them on here that are RF so I think you'll be fine on that. If you're just building a warming cabinet I don't think you'll need an inlet from the FB, radiant heat should be fine. You will probably need to make an adjustable vent on the WC so you can keep it at 140 degrees. jm2cw

[Big T]

Maybe this will help you out viewtopic.php?f=11&t=2448

[Mmmmm]

So here's the options:

Offset-


Reverse flow-


Offset with vertical section -


Reverse flow with warming cabinet -


Reverse flow with vertical section -


Give me your vote fellas. I'm itching to start cutting.

[Pete Mazz]

RF with WC.

I'd build the WC with a small stack and a bottom inlet to the FB in case you want to use it for a small cook. You can cover it when going RF.

[Rodcrafter]

I agree with Pete

[SmokinFF]

I agree with RC who agrees with Pete.

[The Czar]

The most tried and true will be the RF with the WC....

[Mmmmm]

Thanks, fellas. I'm gonna build the RF with a WC. I will cut a 4" hole with an adjustable damper in the top of the WC and if I'm lucky I might be able to build a hot enough fire to actually do some cooking in the WC. If not it'll for sure keep cooked food warm. Thanks for the replies.

[Grabber70Mach]

I would go with RF w/wc.

From infinity and beyond

[Rev.Mike]

[Mmmmm]

Now you guys got me fretting about warped doors and light gauge metal headaches. To help mitigate the warping, is there any reason why I can't just stitch the flat strap to the door with little stitches front and back and then seal it up around the front with high temp RTV silicone? It's seems like there would be a lot less chance of fighting it if I wasn't trying to weld a solid bead all the way around the door.

[Rodcrafter]

Yes that does work stagger them and let it cool a bit and do some more.

[Mmmmm]

OK Thanks! My brother in-law works at a fab shop and they have a CAD operated plasma table so today he's cutting the 1/4" plate steel for my fire box complete with vents and door opening so this project might get underway yet. I'm planning to use some 1" woven steel gravel screen that we have laying around for my fire basket. I think I'll be in this thing for very little money. Hope it cooks well.

[BBsSmokeShack]

I'm building a RF with WC out of a 250 gallon propane tank. The warming cabinet is really going to be an extension of my cook chamber with the flue on top of the WC...sort of following the Bubba Grills approach. I know quite a few guys cooking on them and they have nothing but good to say about them. Now to find money for steel

[The Czar]

Because it's such thin metal… Like RC said… Staggering your stitch welding…will help

[Mmmmm]

Because it's such thin metal… Like RC said… Staggering your stitch welding…will help

Whaddya'll mean when you say stagger the welds? Are you saying weld for example a stitch every 3" on the outside and the same on the inside but spaced between the outside welds? Or, do you mean weld one stitch inside, one outside, one inside, one outside, possibly in exactly the same locations but just in and out, in and out to even out the heat distortion all the way along? The second makes sense to me, the first not so much, can't see why it'd matter.

Please try to explain while I hide behind my phonics workbook and scratch my beau's initials in my desktop .

[Big T]

Just move your welds around, weld an inch on one side and then an inch on the other side. Keep moving them around and don't let the heat build up in one spot, if it starts getting hot just stop and let it cool down. I know you want to hurry and get it done but if you get it too hot it will distort the shape and you'll spend a lot of time trying to get it to fit right.

[Mmmmm]

Gotcha. That's what I thought and that is what I would've done anyway.

[Big T]

[DUAYNE B]

[The Czar]

BigT beat me to it....thanks bro

[Mmmmm]

I think it's inevitable that I'll have some door fitting to do given the thin gauge of the tank. In theory if I really watch my stuff as I progress I can use the heat shrinkage to my advantage. Tack a couple, hold it up, if the radius is too big weld a few tacks inside, if it is too small weld a few on the outside, and across the top and bottom just go back and forth and sight it often and if it's getting sprung one way or the other put a couple extra tacks on the outside of the bow.

No?

[The Czar]

Now your thinking smart!!

[Mmmmm]

Well, I've been cutting and welding and now have the FB mostly built, the stand partially done, the BP cut, and the tank bell end cut to receive the FB. I'm looking at the work going into this thing and the thickness of metal I'm working with and having second thoughts about welding a pop can thin CC to all this thick steel.

The FB is sized for an 80 gallon tank. I've got a few ideas rattling around in my head. If you were me, would you:

Continue with the build since I already have a free, albeit thin, tank in my possession with nice dimensions?

Find a piece of 1/4" wall pipe with a 20" diameter that matches my tank since the throat is already cut out of the FB, cut it to length to achieve 80 gallons, and weld flat ends in it?

Cut the bell ends off my tank and weld them on a chunk of matching diameter 1/4" wall pipe equal in length to the section I replace? The bell ends would still be thin but the benefit would be the airflow characteristics of the bell ends vs a flat end.

Bear in mind I don't have a lot of cash to go buy a piece of pipe, but I might have a lead on some used stuff for pretty cheap.

What do the gurus think?