Reverse Flow 300L Air Tank Build in Greece...$20 Stick Welder and Angle Grinder

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alfa01

Fire Starter
Original poster
Jan 5, 2017
46
12
Howdy!  

Mississippi boy living abroad in Greece building a reverse flow from a 1970's 300 liter air compressor tank.  I found the tank last week at the scrapyard and immediately went to work.  

 
Started by cutting the ends off and getting it down to a manageable size, but still leaving it big enough to get a pig in there.  


Also cut off the old feet that held the tank.  Man, that is some thick steel.  Built in 1973 as I discovered from the ID plate. The feet on this thing must have beet 3/8" steel...they built them sturdy back then.  


Both ends off and the welds for the feet ground down.  I'm leaving the motor mount on the top until later as a way to find level easily and reference for marking doors, leg mounts, etc.  
 

This old tank had a massive amount of rust inside it from years of neglect and probably from not draining it properly.  Those old compressors built up a lot of moisture and typically cause rust when the tanks weren't drained and taken care of properly.  

Decided to tilt it up on the side and burn it like a rocket stove.  I let air under one side which really fed the fire well and caused it to burn pretty hot.  Got rid of the rust and most of the paint.  Also, got rid of my garden and yard debris. :)
 

I took the ends of the tank and welded them back together to for a firebox.  I had planned to build a square firebox, but after seeing how thick this steel for the tank is, I decided to use it.  Planning to cut out the top and add a flat top in order to attach a warmer/rib box.  

Door frame added.  30cm square opening for the door.  


 
Nice work.   You may want to raise the firebox on the cook chamber, it looks a little low.  

Don't de afraid to ask questions, there a lot of experience on this forum
 
 
Nice work.   You may want to raise the firebox on the cook chamber, it looks a little low.  

Don't de afraid to ask questions, there a lot of experience on this forum
Yeah, it's a lowrider!!!  Haha.  No, seriously I just propped it up on scrap steel and a lawn chair to check my cutting.  Wanted to make sure the main chamber and firebox would mate up properly so I can get a good weld on it.  It has quite a bit of clearance in there.  Not sure what gap to keep between bottom of main chamber and top of the firebox.  I was using the calculator over at Feldon's site.  According to the calculator, I need about 62 sq inches.  By my rusty math skills, and some handy online calculators, I'm sitting at a volume of 185 sq inches for the opening I have currently.  Fingers crossed that it's good.  

Thanks for the reply!

Cheers,

Dan
 
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Yeah, it's a lowrider!!!  Haha.  No, seriously I just propped it up on scrap steel and a lawn chair to check my cutting.  Wanted to make sure the main chamber and firebox would mate up properly so I can get a good weld on it.  It has quite a bit of clearance in there.  Not sure what gap to keep between bottom of main chamber and top of the firebox.  I was using the calculator over at Feldon's site.  According to the calculator, I need about 62 sq inches.  By my rusty math skills, and some handy online calculators, I'm sitting at a volume of 185 sq inches for the opening I have currently.  Fingers crossed that it's good.  

Thanks for the reply!

Cheers,

Dan
Recalculated for area instead of volume and came up with 62.31.  According to Feldon's calculator, I need 62.85 so I'm going to widen it just a bit to gain a little area and then weld it up.  

 
Remember to add a grease dam of at least 1 inch into that calculation.    Dave O's numbers are about 30% more for Fb/cc opening
 
 
Remember to add a grease dam of at least 1 inch into that calculation.    Dave O's numbers are about 30% more for Fb/cc opening
I actually trimmed it another inch today to raise the firebox and welded on the end plate for the main chamber.  It's raining a lot this week, so I'm a bit slow to get stuff done.  Worked on the firebox door a bit.  

The calculation from Feldon's is for a half moon.  I actually have an elliptical opening.  Not sure if makes a bit of difference, but it sure does make the calculations interesting.  

The grease dam is on the agenda.  I'm planning for a grease drain with ball valve and a dam to prevent it from running back toward the firebox.  
 
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Hey Dan, you only used an angle grinder to cut through that thick metal?
Yep.  Just cut out the end plate from approx 1/4" steel.  Surprising thing is, the steel from the tank is thinner, but seems to be much higher quality than the new steel I bought for the end caps.  It was sure a lot more difficult to cut.  It seems to weld better too.  

It's a bit of work and I eat up some discs, but discs are cheaper than buying a plasma cutter.  I use the super thin discs for cutting stainless.  They flex a bit and take away a lot less material, so it makes it easier.  

Cheers,

Dan
 
Thanks Dan, I know, I'm wondering if I should find someone with a plasma cutter and pay them to simply cut the metal for me. My current barrel smoker I cut with an angle grinder and on the door it took away about 1/8 of an inch which I want to avoid in making my new one. I'm also going to reenforce the door, unlike I did last time. Thanks again, I bet folks over in Greece are loving a taste of the south!
 
A plasma cutter will take more than an 1/8 inch when you make your cut. Any way you cut it your going to loose some material.
 
 
Thanks Dan, I know, I'm wondering if I should find someone with a plasma cutter and pay them to simply cut the metal for me. My current barrel smoker I cut with an angle grinder and on the door it took away about 1/8 of an inch which I want to avoid in making my new one. I'm also going to reenforce the door, unlike I did last time. Thanks again, I bet folks over in Greece are loving a taste of the south!
These discs are approximately 1/16 or so, less than an 1/8 for sure.  I think the last ones I bought were from Makita.  The plasma will probably take away significant amount of metal also.  Maybe if you find a laser cutter or waterjet, you can reduce that loss and gain some tolerance.  

Most of the folks I knew back in MS, used acetylene torches to cut the thick stuff.  I don't have one at the moment, and I really wanted to avoid the heat warp, nasty cuts and clean up that a torch can leave behind.  

I'm working on reinforcing my door on the firebox as well.  I'm afraid after time, it will warp and leak if I don't.  I do a lot of smoking for holidays and bbq's with friends.  Everybody digs the pork shoulder, boston butts and pork bellies.  I make a pretty mean bbq sauce which goes over real good too.

Cheers,

Dan
 
Doesn't really matter if it takes some metal, you are going to cover it with a strip of flatbar.

A little gap will stop the door binding.    after you are done cutting the door out, mak nothces every 5" with the grinder and tack weld the flatbar on the inside, so it gives you a clean look on the outside.

I cut    2-3  tanks/ tubes a week with the plasma then a quick dress up with the grinder.
 
I used a plasma cutter when cutting my tank. It's the fastest way and much cleaner than a torch. I agree having a gap makes the door much easier.
 
Yeah I see your point. Having it stick is not ideal either.

@Ahumadora what is the flat bar you mentioned above and where can you get it?
 
1/8 x 1"   steel bar that's flat.  Look at 99% of the smokers that use it for door seals.     

Any place that sells steel has it.  You can bend a curve in it easy enough by wrapping it around the door with your hands.

Don't go nuts welding it onto the door, it only stops air.  The more you weld it, the more likely the door will warp from the heat.
 
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