Gravity feed burner on a offset shaped cooking chamber

[PetesMeat]

Hi All,

I promised myself that the next smoker I built would be gravity feed.

Problem is, I just moved my company into a new building and there was this massive old air compressor from the 60s hidden in a shed out the back, so i have no choice, I HAVE to make it into a smoker, its the law.

So now I want to make a gravity feed burner, but using this old air compressor tank as a cooking chamber. The tank was made in England, and its so old it predates wide use of metric in the UK, so the dimensions on the tank ID plate is in imperial units, which is odd for me. The tank is 20x60 inches, 20 diameter, 60 long.

So, what im wondering is, has this been done before? I see gravity feed smokers are usually cabinet types, insulated and upright. I plan on putting the burner in the middle, with a baffle, with the exhaust in the middle. I have a similar setup on another smoker I built, which has a centre feed firebox, a baffle and exhaust in the middle, but its a stickburner type firebox, not gravity feed.

Im obviously nervous, as this is not a very well tried and tested thing, and im worried that I will go to all the effort and expense of building this smoker, and then find out that it reaches 150F and tops out. Im hoping to find some examples of similar smokers so that I can see how big their charcoal chutes are, how big the throat opening is, the grill etc, so I can at least reassure myself that this is going to work...!

I have attached some photos of the tank.


Pete.

[Squiggle]

Frank & the HQ boys should be able to help out with the sizes, but I know that Rodcrafter has put a GF unit on his RF so he should be able to tell you how effective it is.

[KarateDoc]

I was planning on doing this as well. Stump smokers has a gravity fed horizontal pit. I thought about building one that I could put in my mini pickup.

[ajfoxy]

Definitely going to be an interesting build. Look forward to pics etc.

[PetesMeat]

Well, I don't want to give too much away right now about my plans, but I will show you what I have done so far... This is not going to be your typical smoker...

Is there a way to get Rodcrafters attention? Id love to see his RF gravity feed. I will go stalking through the member list and see if I can find some photos :-D

Pete.

[PetesMeat]

Hmm, the forum wont allow me to post photos, it just uploads and then puts a little exclamation mark.



Here is one off facebook.

If your intrigued, go to google image search and search for "iron lung"

Pete.

[Squiggle]

Just send him a PM, that should get his attention.

[Rodcrafter]

Oh it hasn't been that long since I was on the site fellas. I do have to do some correcting though. Squiggle said I have an GF on my RF. But the GF is on the vertical part of the rig above the FB of the RF. Yes it is different but quite amazing. Now there was a guy that did put a large GF burner in the firebox of an offset. It used a lot of fuel but he did say it worked. The GF burner works great, but to make it fuel friendly you really need insulation and the thinner inside skin helps too as you don't have to heat the large mass of steel. I know this is not what you want to hear but, if you turned it on end and put square doors on it you would probably get better results.

But don't let me mess with your plans.

jm2cw

[PetesMeat]

Well i'm not too worried about it being fuel efficient. If I want to be fuel efficient, I have a UDS here I can use. This smoker is going to be interesting, and weird and unusual, and if it eats more fuel, so what, il just keep feeding it. I won't use it that often anyway.

My main worry is that it wont work at all, more than it using too much fuel. Just the burner not getting hot enough is my concern. How big do you think the burner should be Rodcrafter?

Pete.

[PetesMeat]

I have attached some cad models.

To give you an idea, the chute is 250mm square (10inches) and 1200mm tall (4 feet).

The open area that vents into the firebox where all the hot air will come through is 100x250, thats 4x10 inches.

The tank is 500x1500mm, 20x60 inches.

What do we think, is that burner going to be powerful enough? Its a pretty big hunk of metal, the chute is very large when you think about it....

Pete.

[Squiggle]

Looks pretty good dude, I'm thinking you'll need some sort of transfer tube/baffle where the GF unit enters the CC, this will help dissipate the heat & even out the temp in the CC(kind of like a cross between an insulated GF cabinet & an RF style).

[Rodcrafter]

Yes and figure on getting a cyber q so it can have a fan driven burner.


Making memories!

[Pete Mazz]

Are you going to configure this as a CF (Center Feed)?

[PetesMeat]

Yes, going to fabtricate some kind of tube thing to duct the heat into the chamber, and will have a shaddow plate above it to stop a hot spot on the baffle.

It will be a centre feed, I have a centre feed already that works very well. I don't want to do an offset because of the way the doors open on this smoker.

I already have a pit controller, I built it myself using cheap bits of electronics off amazon. It can hold temp inside my UDS within 1 degree F for hours on end. I will possibly need a bigger fan for this gravity feed, but thats no problem.


I have ordered the steel for the base, and im shopping around to get the best price on the laser cutting for the door hinge.

Next step is get the base made and get the tank sitting on the base so its at a nice height to work on, then do the flappy door ends, and then start on the burner.

I have no idea what diameter and height to make the exhaust, so im going to have to kind of wing that, and make them removable so i can change the length after. Upright cabinets don't really have exhausts so I got nothign to base it on. I need a chimney obviously to create the draft effect, but I just dont know how long...

I am wondering if the chimney size is directly related to the air intake size?!

Pete.

[Rodcrafter]

I would go with about a 30" x 4" stack it would look about right and would draw well. As far as the air intake size the fan unit will be that part.

[PetesMeat]

Ok, i was toing to go for two stacks and have the ends turned away, as I have in my centre feed, I think it looks cool and I would like to establish a consistency between them, kind of a signature design feature for all my smokers :-D

The pipe i use is 75mm stainless steel tube, 3 inches. Maybe i could use 2 inch for this one but id rather use 3, looks better.....

Photo of my centre feed and its shiny exhausts is attached...

[Pete Mazz]

3" stack should be ~40". It's based on FB volume.

[PetesMeat]

Thing is with that, the firebox is not a traditional firebox at all, its a lot smaller than a normal firebox would be, so the firebox, according to pitcalc, should be about 6000 cu inch, but instead its 1700, because its a gravity feed, so does that mean the stack should the the size that it would be for a 6000cu in firebox, or should it be the size it should be for the actual size of the firebox?! Its confusing, this gravity feed is a bit of unchartered territory for home builders, especially when its not in a cabinet, so hopefully i can work it out and help others build them.

Pete.

[Pete Mazz]

When the blower isn't on it needs to draw like a normal smoker. It's not a vertical so I don't think it'll draw like one. The heat and smoke still have to travel around the BP, as well as the small size of the intake, which requires some pulling power. If the blower is on all the time the stack can be any length you want.

[chefbrady]

Following

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[PetesMeat]

Hi All,

Well I have made a bit of progress. I got the steel for the chute and tacked it up today.

The steel for the chute is 5mm thick, and its four strips 250mm wide and 1250mm high. This means the finished chute is 1250mm high and 250mm square (thats about 10 inch square and about four foot high i think). The opening is 100mm (4 inch) high.

Its insanely heavy, and this is just the chute. I think its gonna take about 6-7 5kg bags of charcoal once its done. I was worried about the thing not getting hot enough, im not worried about that anymore....!

[mp4]

Your workspace is way, way too clean dude! Nice work!

[PetesMeat]

Hah, its not clean - its new. Its not been filled up yet.

[ajfoxy]

Nice. Good strong work.
Interesting bits of steel with the dogbone pattern cut in you have in the pic with the mallet lying on the steel. Just curious as to what those are for and they appear way too neat for plasma so presume they were laser or waterjet cut.

[PetesMeat]

Ahh, they are not steel. They are PVC antistatic floor tiles. I have a clean electronics assembly lab in the same building and I just laid a floor made of those tiles (you use the mallet to bang the dog bone jigsaw teeth together). The offcuts are turning out to be rather useful...!!

Pete.