T-Shirt cannon pnuematic set ups

[Matt Howard]

About a foot of reinforced concrete.

[billbo911]

Originally Posted by gorrilla

what's the wall thicknesss?

Originally Posted by Matt Howard

About a foot of reinforced concrete.

I think he may have been asking about the pipe.

[gorrilla]

Originally Posted by billbo911

I think he may have been asking about the pipe.

In fact I was

and I never thought that bats could "pop" like that

[jspatz1]

Our Lunacy robot this year used a catapult to launch moon rocks up to 35ft, so it is ready to go as a t-shirt launcher with no changes! Just need to bundle up the shirts into an approximate ball.

[Matt Howard]

Originally Posted by gorrilla

In fact I was

and I never thought that bats could "pop" like that

Lol, that somehow flew completely over my head.

I don't know the wall thickness. It's class 150 Galvanized Steel.

[dpeterson3]

Our team built one about three years ago for school. With the exception of 2 parts, the entire thing is PVC. The tank has been preasure tested up to 60 PSI with no problems. We only need about 20 psi usually, though. Our first attempt, the tank blew off. That was my fault. I didn't clean the PVC well and didn't use primer. Those are very necessary. Now it works great. If the towels (we use rally towels because they are a lot cheaper than shirts) are rubber-banded before they are loaded into the barrel, the go much farther. Our bleachers are built into a hill at about a 60 degree angle below the horziontal. From the bottom,. we can shoot over the booth with only 30 pounds of air. If you want, I can send you preformance statistics, videos, adn a few pictures on what not to do.

Good luck

[Cody Carey]

This is a double post, but I think you guys might like to read it over here, as well.
Hey all... I just wan to clear some stuff up about PVC, and there really isn't a better way to do that then to borrow Some words from a physics prof on a forum I frequent.

I can understand why Fred and others here feel a strong twinge of concern when someone in school suggests using PVC for an air tank. We've all seen explosions from pressurized tanks and pipe, and students don't typically have the experience to know how to design and test pressurized systems. Sure, we've all seen potato guns, but we don't know what it is you're really planning to build, it sounds a bit more sophisticated. And besides, potato guns have been known to explode.

The piping codes in the US apply to these systems. This would fall under ASME B31.3, Appendix A. Note appendix A refers you to the main body of the piping code for most calculations. I'll be using this as a guide to make suggestions.

Regarding materials, PVC pipe falls under ASTM D 1785 or D 2241. The fittings fall under a variety of ASTM standards including ASTM D 2464, D 2467 and D 2468. There are others. If you decide to use PVC, one thing that would help ensure safety would be to verify one of these numbers is printed directly on all the pipe and fittings you use. If they don't have these ASTM numbers printed on them, they probably don't meet the minimum standards and shouldn't be used.

Cements used for PVC pipe should meet ASTM D 2564. Verify the stuff you purchase meets this code. Follow the directions on the can.

None of the pipe should be threaded except for purchased fittings. Everything should be glued using the appropriate cement. If you cut any threads, you're doing something dangerous.

At 70 psi, you have a roughly 3 to 1 safety factor on top of the standard safety factors. The "stress allowable" for PVC at 100 F is 1.6 ksi which says the pipe is good for roughly 210 psi operating pressure. If temperature exceeds this, the pressure rating drops off very quickly, I'd not recommend it above this temperature. The code also prohibits its use below 0 F. If the plastic gets cold, which it could because of the expanding gasses doing work on whatever, wait till it is warm again before pressurizing. Cold plastic is more likely to break.

Consider what external stresses you are imposing such as bending of the pipe between supports. The pipe should be reasonably well supported over long sections.

Once you've manufactured the piping, do a pressure test on it using water. Fill with water, make sure there is no air in the system, and then pressurize to at least 200 psi, preferably 300 psi. Hold this pressure for 5 minutes, then release the pressure and verify there are no leaks or distortion of any part. If it holds this pressure, I'd feel a lot better about using it.

I'd also suggest repeating this pressure test every 100 cycles or whenever you suspect damage or leave it sitting for extended periods of time. Cyclic pressure and other uncontrolled factors could damage the piping, regular testing will help prevent catastrophic explosions.

Verify all valves you use are rated for the given pressure.

You really should have a relief device, set at about 100 psi, immediately downstream of your regulator, just in case the regulator fails.

For a pressure source, do not use any source of pressure above 150 psi. High pressure cylinders are extremely dangerous.

Off hand, I can't think of anything else to warn you about. Maybe the others here could suggest specific considerations.

In short, as long as everything is set up correctly, and safety checked multiple times, tehre is very little that can go wrong, especially while operating at 100psi and under... a 2 to 1 safety factor on top of standard is really good.

I'm not saying this is a good Idea, but people in my local offroading club have been using PVC as air tanks for portable systems for years. They mount these on bottoms of bumpers, roll cages, and other places where they are almost sure to get hit, and HARD. When I went to my first meeting and saw that, I remembered threads like this from when I frequented CD and asked if they'd ever had any blowouts or problems associated with this, and I was surprised to find that there had only been one... And it had happened when the guy forgot to put PVC cement on an end cap.

Hows that for working in the real world?

As a side note, the reason he says to test the system with liquid is because at pressure, the main difference between water and air is that air will explosively expand when a crack or weak spot is formed, and water won't. This means that if you have a leak and fill it with water, you won't have any sort of explosion, and if it holds up for five minutes at 200 psi, you know you won't have any problems below 100.


Then again, It's pretty easy just to weld up a steel tank.

[Matt Howard]

Guys, its not difficult or that much more expensive to just use steel.

I would have thought by this point of the thread everyone's opinions would have drifted that way, and I'm really surprised that it hasn't.

Steel is far stronger, safer, and tolerant than PVC is.

Long story short, if you want an air cannon, you want steel.