T-Shirt cannon pnuematic set ups

[EricH]

Originally Posted by Mr. Freeman

No offense, but I could ask you the very same question. I don't think you've explained what degree you hold.

Neither have you, programmer. What materials courses have YOU had?

As for the original question, I'm pretty sure high school students don't have degrees in engineering. They may have experience or expertise in doing stupid things, but I'm not sure I'd trust that.

On the other hand, a mentor whose rookie year was 1999, even if he was a freshman in high school at the time, would most likely have an engineering degree by now and a year or so "in the field", minimum. If said mentor is in any form of mechanical, materials, civil, or possibly even industrial or electrical engineering, I would be willing to bet that he's had at least one materials course, and possibly more. There's a chance even if he's more of a computer type of engineer. If said mentor was older than a freshman in his rookie year, it's still more likely that he's had both the education and the experience.

If I had to choose between a high school student with no training other than experience in doing things that aren't necessarily safe and a mentor who's most likely had the training and the experience of doing things the safe way, but not guaranteed, I'd take the mentor every time.

[Mr. Freeman]

My point wasn't to start an argument about who has taken what classes here. It was more to emphasize that asking people rhetorical questions in an insulting manner isn't the best way to solve this PVC vs. no-PVC argument.

Anyway, in another thread about air cannons someone mentioned that what actually causes PVC to fail when using it with compressed gasses is the shock loading. I haven't seen that mentioned here, it's probably important.

[Tom Line]

My original post had a good dose of sarcasm - I get that way when I see someone putting others in harms way with no good proof.

Here are a few more resources:
http://www.articlesbase.com/technolo...ld-495648.html

http://www.lni.wa.gov/Safety/Basics/HazAlerts/902.asp

http://erd.dli.mt.gov/safetyhealth/b...dgassafety.pdf

Here are some wonderfully instructive videos on what happens:
http://www.crazybuilders.com/forum/showthread.php?p=29

http://www.astm.org/Standards/D1785.htm

http://www.ppfahome.org/pvc/index.html

If, by now, this discussion is not at an end, I the person here said it best:
http://www.garageofevil.com/faq/showdoc.php?id=35

If that does not answer the question as to why you should not use it for this purpose, you should add yourself as a corpse prop to your haunt now.

[Matt Howard]

Now that this thread has been completely hijacked by an Ego contest....


When I built my air cannon in high school, I had the help of my father who has worked in Water Treatment for about 30 years, so thankfully I was blessed with knowledge from above about pressure ratings.

I used 4 inch Galvanized Steel, and typically ran it at 135 PSI.

I was able to launch aluminum baseball bats about 250 yards with about a gallon of water in the barrel.

Enjoy some very dated pictures:

[billbo911]

Originally Posted by Matt Howard

Now that this thread has been completely hijacked by an Ego contest....


When I built my air cannon in high school, I had the help of my father who has worked in Water Treatment for about 30 years, so thankfully I was blessed with knowledge from above about pressure ratings.

I used 4 inch Galvanized Steel, and typically ran it at 135 PSI.

I was able to launch aluminum baseball bats about 250 yards with about a gallon of water in the barrel.

Enjoy some very dated pictures:

The wisdom to take from this post is that the pressure tank was built out of steel, not PVC. Secondly, from the looks of what was built, I would say it really didn't cost that much to build either, and could be easily reproduced.

Now my next question.
From the looks of the pictures, that shattered bat happened before it hit the ground. Take a close look a the bottom of the picture showing the canon firing. Look at the shadow, it looks like the bat has broken already. Is this correct?


BTW, I love the use of water to seal around the bat and act as a sort of Sabot! Besides, it looks AWESOME!

[Matt Howard]

It was actually somewhat expensive to build. The 4 inch galvanized steel pipe with all the fittings was about $160 at a pipe house. Also, large pipe wrenches were required to assemble it.

The result however, is something I wont have to worry about overcharging, as well as insanely durable.

I'm going to have to say, yes the bat was broken.

We Launched it across a field into the back of a concrete wall just to see what would happen. (This is what happens when freshmen and sophomores are left unsupervised with an air cannon) Turned out the bat launched far more effectively after the end had broken off, as the inside of the bat was hollow, and allowed for a sort of "rocket" effect.

Oranges are great projectiles, as they explode on impact like a paintball. Never actually tried a potato, but considering that this is more of a pneumatic "anything that will fit into the 11 foot barrel cannon".....

[gorrilla]

Originally Posted by Matt Howard

It was actually somewhat expensive to build. The 4 inch galvanized steel pipe with all the fittings was about $160 at a pipe house. Also, large pipe wrenches were required to assemble it.

The result however, is something I wont have to worry about overcharging, as well as insanely durable.

I'm going to have to say, yes the bat was broken.

We Launched it across a field into the back of a concrete wall just to see what would happen. Turned out the bat launched far more effectively after the end had broken off, as the inside of the bat was hollow, and allowed for a sort of "rocket" effect.

what's the wall thicknesss?

[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.