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# Thread: Anyone Ever Built an Air Tank?

1. ## Propane Tanks

I wouldn't do it! Propane tanks are made of about 16 gauge steel and never see moisture.

2. DSW
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Originally Posted by platypus20
as a cubic foot of air is the air volume in 3' x 3' x 3' box at atomospheric pressure.
How is a cubic foot = to 3 feet X 3 feet X 3 feet? My math works to a cubic Yard or 27 CF. Your other calcs make sense to me, sort of. I know 14.7 psi is equal to air at sea level and you need to add that to anything if you are calulating absolute presures.

I usually work from a known volume say 104 cf @ 2640 psi and then calculate CF basied on presure so at 1320psi you have 52 cf. The math gives you 1 cf @ 25.38 psi. That same tank would hold a bit over 165 cf if you could push the psi to say 4200psi.

Wonder if portable, (diesel driven) compressors fall under this same inspection?
I'm trying to remebmber most of the portable diesel comps I worked with when I worked at the comp shop. I know they are mostly rotery screw machines and I doubt that they have a "tank" if so its a small one. I would guess that they run air straight from the compressor as those screw machines generate very large volumes of gas so storage would not be required.

3. Originally Posted by DSW
How is a cubic foot = to 3 feet X 3 feet X 3 feet? My math works to a cubic Yard or 27 CF. Your other calcs make sense to me, sort of. I know 14.7 psi is equal to air at sea level and you need to add that to anything if you are calulating absolute presures.
Yes you are right, my mistake that a cubic yark, not a cubic foot, which is 1' x 1' x 1'. sorry

Jack

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## Propane Tank

Look into a large horizontal propane tank. The two most popular sizes are 500 and 1000 gal. They are built to an ASME standard. They have a ASME tag. IS there a difference between the standards of an air tank compared to a propane tank?? I had a 1000 gal size i bought from a propane supplier, the ASME tag had been knoked off of the tank and they were no longer allowed to use it. After i bought it i filled it with water and then did a hydro test to 300 psi, double the 150 psi that a portable screw compressor made. I used it as a resivor to blow steam whistles.

Weekend Welder

5. ## PSI is PSI

So, you fill a air tank with 15 psi. Then you fill another tank with thicker walls, it's still the same. I've worked with hydraulics for a long time. 150 PSI is nothing. If that tank explodes, it'll just crack a seem and leek out. There will be no explosions at all. Look at gas cylinders, 2500 PSI, stored on service trucks. There is no problems with that. Still, no propane tanks in my opinion, should be used for compressed air. They are too fat in diameter. I'm not an engineer, but happy with my homemade setup.

Thanks,
Lance

6. Originally Posted by lanceman73
150 PSI is nothing. If that tank explodes, it'll just crack a seem and leek out.

Thanks,
Lance
I saw a portable air tank explode on my dads leg. He was in the hospital for a week. The tank had a crack about 12 long in the welded area and opened right up against his leg...Bob

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nj
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Originally Posted by lanceman73
So, you fill a air tank with 15 psi. Then you fill another tank with thicker walls, it's still the same. I've worked with hydraulics for a long time. 150 PSI is nothing. If that tank explodes, it'll just crack a seem and leek out. There will be no explosions at all. Look at gas cylinders, 2500 PSI, stored on service trucks. There is no problems with that. Still, no propane tanks in my opinion, should be used for compressed air. They are too fat in diameter. I'm not an engineer, but happy with my homemade setup.

Thanks,
Lance
You are most certainly correct: you are not an engineer

Air, or other compressible fluid (gas) is NOT hydraulic fluid. Compressed gasses store much, much more energy than liquids. The stored energy is available to do a great deal of damage in the case of a failure. Rough rule: 40gal of air compressed to 100PSIG is equivalent to one stick of straight dynamite (if you ar about to respond 'no one here knows what a stick of dynamite is', you are missing the point: even if you have never used it, you wouldn't hold a tin can with a stick in it while it was detonated, nor would you want it in your home.)

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## For the Record...I built my own compressor tank

Actually my dad had me make a replacement tank for our 1.5 HP 2 cylinder WW Grainger compressor. The twin hotdog tanks rusted out and they were very thin metal wise. My dad had purchased 8" weld on cap ends from a pipe supplier. These were rated as Sch. 40 for pressure application on underground lines. He had me cut a section of 8" Sch. 40 steel pipe to make the body of the tank from. Anyway, my dad said that this compressor will never be sold to anybody cause it doesn't have the ASME / ASTM tags to go on it, because it was home built basically. I welded in couplings and transferred all connections and safety devices from the old tanks to the one I built. Max air pressure is 125 PSI. I cut the compressor mounts and handle from the old tanks and welded them to the new tank I built.

Also, as part of our storage system, we are using a 40 gallon Butane Tank from an Oliver tractor. My dad had come up with two tanks from scrapping out two tractors. One of the tanks was bad, big hole in it from being run into by something. Anyway, the tank wall thickness was pretty thick, 3/8". So my dad put 125 PSI of air from our shop compressor on the other tank and soaped all the fitting and joints and let the tank set. It held air and didn't appear to have any leaks around the fittings. That tank is still used to this day for our air storage.

When I was at Texas Tech studying Mechanical Engineering, my faculty advisor and Thermodynamics professor related a story from Oak Ridge National Labs. After WW2, the lab was using surplus torpedo tanks for air storage. They were compressing air to 4200 PSI. One day, someone asked what would happen if one failed. My professor described the tanks from the torpedoes to be about 24" in diameter and about 20 ft. long. The tanks had been nested in racks about 3 tanks high and 5 tanks across. Well, to answer the question about what would happen if one failed, they took one out to a large open field and purposely caused it to fail with the 4200 PSI air charge on board. The destruction from the blast and flying shrapnel was described as a tiny nuke. After seeing what happened, the storage pressure was reduced to 2400 PSI and the nesting was changed. The tanks were stacked 2 high, and had steel plate between each stack of 2 tanks. Also, the tanks were housed in a hardened blast house in such a way that in case of another failure the shrapnel and carnage would be directed away from people and buildings and out into a "blast zone". That is the story he told us in class one day while we were studying about high pressure steam turbines.

From personal experience, I have seen what 60 PSI and 200 gallons of water can do on a galvanized pressure tank that the bottom weld gave way on. The tank in question was a 300 standard air pressure tank. About 3-1/2 ft. in diameter and around 7 ft. tall. The bottom of the tank was still on the floor of the well house when we arrived to replace it. There was a big gaping hole in the roof of the metal frame and sheet metal well house. All of the plumbing and control wiring was gone, it flew with the tank and was strewn out from the well house to were the tank landed some 300 ft. away.

That's all I have to share on this.

Charlie

9. Happened to be watching some "Mega Marvel Something-Or-Other" TV program about building tires and high-end mountain bikes. The statement was made that a 70/70 mountain bike tire, filled to 120psi had enough energy to blow a 200# man to an altitude of 10,000 feet!

Now, I don't know if that is true or not, but they said it right there on TV, so it must be.

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You think that makes sense?

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