Custom Air Tank Questions.....

Hello max, ive never posted in the "Ask Max" section, so here is my first go at it.
 
Im considering making a custom air tank for my ram.  My reasoning is that i need a shallow air tank, 6" top to bottom, to fit in a location that will serve me better.
 
I have a pair of options that i would like to know which you feel would be more suitable, and why.
 
My first option is a piece of  6x12 rectangle tube steel, with a 3/8 wall thickness, or possibly thicker......  I would weld in a plate on each end of the piece to seal off the tank area.  then drill and weld in bungs for air managment.  Im considering about 24" legnth.  
 
My second option is waterjet cut out the individual pieces i need for each panel of the tank, and weld them all together.  It would be from 1/2 or 3/4" thick material, and again roughly 6x12x24.   With this tank, i would probably water jet cut the right size holes ware i need them, then tap them for a pipe thread. 
 
I have some very experienced welders at my disposal, the shop i work at auctually makes pressure vessles, for big ass stoves, and its no problem for me to have one of them weld all my seams for me so that it takes that varriable out of the equation.
 
 
Which of the two options do you see being the better plan.  The first one i see as being better because there are less seams.  But, on the second method, i can use thicker material, but the seams would come into play.
 
How do you feel about the tank being rectangle?  i know thats normally a bad idea, but with the wall thickness, do you think it will be allright?
 
 
i appriceate your input.
 
 
 
Taylor

Hey Taylor, Ive have my home made tank (rectangle) over 4 yrs with no leaks and it works fine. See my Pic in profile. Just an FYI.....

thanks for the reply man!     can you give me some details on the materials you used?     thanks again!!!       Taylor

Great question!  Was thinking about doing this myself but I was thinking on using a piece of 6x6 1/4wall and capping the ends.  I would think that if you did in seperate pieces that thick Taylor your tank would way 100lbs or better.  Curious to here what Max has to say about this one...

The front crossmember on my frame is a piece of 2x2x1/4 that I capped, drilled, and welded in bungs. It's kind of a Air Distribution block. I have my front 2 valves coming off it...compressor goin into it...air gauge coming off...and a drain cock. I pressure tested my entire system at 250 without any problems. I know that's smaller than what youll be running but I don't think 1/2 will be necessay. I think even 3/8 might be overkill...but that's just a guess. I'm also interested to see what the Great One has to say......   P.S.....Max you coming Tex Mex. Quite a crowd coming from Cali....there will be a cooler full of cold ones waiting on you....

I recently built two out of 5x5 to go under the bed of a truck for load helper and tire filling purposes. I used .188 wall tube, and they where rather heavy. I capped the ends with the same thickness plate. I pressure tested it to 300 PSI with nitrogen, and the schraeder valve blew up. Scary. So I tried it at 200 PSI with better luck. I tried to check it as best I could with a caliper to see if it had ballooned at all from atmospheric pressure to 200 PSI. I noticed no difference, but I could only measure 2" in to compare with the caliper.   I feel like 3/8" is pretty thick, and probably overkill. But with 6x12 tube, I imagine the center would want to give more since there is a larger surface area. If I where to build one by your dimensions, I would probably use 1/4" wall tube, and I would put a gusset on the inside of the tube in the center, with some holes cut in it. Basically a brace the same size as the end caps, to add more rigidity from the inside, and the holes would ensure that you didn't build two tanks in one package. I think that makes sense.   If you build it out of tube, I would make pipe bungs and weld them in.

The problem with tanks built out of flat plate is that the stress can not be spread out like it can with a constant circle. Take a 12" long piece of 12"x8" box tubing. With only 100psi in it, the flat sides will see a force of 14,400 pounds. That is a lot of force! You can cut that stress in half by running (2) 12" long 6"x8" box tubing tanks instead. Thicker wall tubing will of course help out, but at the cost of weight and money.   So on this subject, I have little by way of a difinitive answer. If you are going to use square tubing for your tank, keep the cross sections to a minimum.

Edited: 3/3/2009 9:51:32 PM by UnusualFabrication

If your going to use tubing to brace the inside you could make it a little longer than the tank and  drill holes perpendicular to the tubing to allow air inside the tubing.  Then all you would have to do is tap the tubing.  That way you wouldn't have to add extra bungs.  The tubing would be dual purpose.

well, the material thicknes i was choosing wasnt becuase i enjoy wasting money or anything, but thats the stuff i have available to me for free from work.  We work with alot of thick ass structural tubing, and i usually get my pick of the drop pieces that a cut offs not being used.  We really dont have anything thinner than .375 wall tubing.... there is some .250 wall DOM tube, but its smaller diamiater than i can use.  And i figure its better to be strong and solid, and free!!! haha.   What i found today was 6x6 .375 wall tubing.  Im thinking of running two seperate pieces of that, at 30" long.  Ill make the end caps from the same .375 material, and i will also weld a X on them on the inside to keep them from bowing.   I cut a center section piece out today, what i did was run a 1.25" drill bit straight through the tube from one side to the other, and im welded in a piece of 1.25"x.250 DOM and machined a washer to weld onto one end of it, so i can throw a bolt in it from the bottom, and a socked with an extention and that brace piece will double as a mount on my x-member.   Im laying out the ports i want to have on the tank, and im having them water jet cut tommorrow.     Thanks for the advice and info everyone!     Taylor

it is crazy to think you can get that much force at only 100 psi.   What about the guys that use there frames at air tanks?