SpudFiles

Hey Guys,

I wanted to share a picture of the tank I just built for a 1-1/4 inch bore cannon. It consists of two steel hemispheres from Wagner industries in Milwaukee Wisconsin. They cost $4 each. The straight portion is a piece of 4 inch exhaust tube. All total, I have $16 invested in this tank. I pressure tested it (yes, it was covered and behind a steel door when I tested it) to 275 psi and it held fine. I have one very tiny air leak at one weld. I will fix that tomorrow. It is truely microscopic, though.

Anyway, I will use a 200 psi blow off valve. I figure if it held 275 psi, 200 should leave a safe margin for error.

I will post a build thread when I get more of this cannon built.

Matt

It would be a better idea to test it to , let say 3 or 4 times higher pressure than you plan to use with it

It is a good idea to fill it with liquid such as water when testing so a failure will be low energy instead of high energy with an explosive release.

Look up Hydrostatic testing for more information on this testing method.

Your tank appears to MIG welded........is it?

It is, indeed, MIG welded. I do not own a TIG. I used to do MIG welding for a living. It comes second nature to me.

Great idea to fill it with water for testing. I never considered that!

This tank is .062" wall (The exhaust tubing is). The end caps are .120" wall.

I spoke with an air tank manufacturer yesterday regarding tube thickness for a tank. He mentioned that they sell tanks that are burst rated at 3 times the useage rating. He said a 6 inch diameter tank would be speced by their company at .120 wall steel. That means a .120" wall tank would be good for 600psi. Therefore, they would certify it at 200psi. A smaller diameter tank can tank more pressure per wall thickness. So, this 4 inch diameter tank should be perfectly fine at the 200 psi I am looking for.

Besides, my compressor is only good up to 275 psi. So, that is the highest pressure I can apply to it.

Of course, I could always run CO2 off my welding tank to it to give it 400 psi as a test.

Matt

lokking at that would the disposabul mig gas bottls make a better reciver

propane tank like used for torches will take 200psi all day long

http://www.spudfiles.com/forums/propane ... t9313.html

metalmeltr wrote:propane tank like used for torches will take 200psi all day long

good point, a disposable propane tank would make a great tank. i would even take it to 300psi and it would only take slight modifactions.

or do like me and use a 20lb propane tank, now thats ALOT of air

That means a .120" wall tank would be good for 600psi.

Do you know what equation they use to get those numbers? What it the steel grade(or tensile strength).
I'm just wondering because those big propane tanks are tested to 300 psi and they are much bigger and thinner than the one you describe.

Have they actually caused a failure with a 600psi test?

Fnord wrote:

That means a .120" wall tank would be good for 600psi.

Do you know what equation they use to get those numbers? What it the steel grade(or tensile strength).
I'm just wondering because those big propane tanks are tested to 300 psi and they are much bigger and thinner than the one you describe.

Have they actually caused a failure with a 600psi test?

Not sure about the tensile strength.

I have thought alot about this. Assuming the weld integrity is good, even a mild steel tank can have pretty thin wall and still tolerate a huge amount of pressure.

The Propane tank is a cool idea. However, I needed more than twice the capacity of that tank anyway. As it is, this tank is somewhere around 1.3 to 1 ratio to my barrel. A small propane tank would not be big enough and I do not want a large diameter tank at the end of my cannon. I looked for a number of different tanks to use and ended up with this tank. It works for its intended purpose.

Matt

for 200psi even pvc would work, but not when its cold though

I managed to put a D cell battery through a washing machine with a 1.25 inch barrel and a propane tank chamber. What kind of power do you need?

Technician1002 wrote:I managed to put a D cell battery through a washing machine with a 1.25 inch barrel and a propane tank chamber. What kind of power do you need?

Wow, that is so cool!

I am not looking to blow holes through cement walls or anything. I just figured, hey, if I am going to build something, it may as well be powerful!

Besides, I have a few friends who are really into firearms. They get a thrill out of huge power and massive recoil. When I mentioned I was building an cair cannon I got the typical "Let us know how it works out for you....." Comment that was meant as a "Why mess around with kiddie toys?" So, I want something with a lot of punch.

Oh, I fired my gun on video (just as a test rig with no grip). Funny thing, it was freakin LOUD, but the video just records a very quiet "Snap" sound. Strange.

Anyway, the muzzle was 5 feet from my chronograph and the air blast moved my Chrony back about 2 or 3 inches. It is visible on the video.

Oh, that shot was with a 25 gram slug and recorded 676.8 fps at 200 psi. Not too bad. I wonder how much energey that was. It blew completely through my box full of towels that I use as a back stop. I guess it is time for a better stop..............

Matt

I might as well post the photo. It is located in several threads. Yes a single propane tank with a 1.25 inch barrel can punch a hole in a washing machine at 100 PSI. I don't find the chamber too fat to be difficult to handle.


Some day when I have a source of higher pressure, I will test some more. In theory, that launcher should be good for up to 300 PSI.

If they want massive recoil, build a high pressure soda can launcher. I've had friends get knocked on their butt launching soda cans.

The larger version launches full cans of soda pop. Watch the recoil.

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High-PSI wrote:Oh, I fired my gun on video (just as a test rig with no grip). Funny thing, it was freakin LOUD, but the video just records a very quiet "Snap" sound. Strange.

I think either your camera or computer is adjusting the recorded volume, I've had this happen to me before and am almost certain that's the cause. I don't know that you can do anything about it, sadly.