T-Shirt cannon pnuematic set ups

[Mr. Freeman]

Originally Posted by Tom Line

I wonder what type of professional engineering or material engineering degree this person has.

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

[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.

[RyanN]

Originally Posted by Mr. Freeman

I don't think the size of molecules changes when changing states from liquid to gas.

Is liquid not thicker than air? Try to move your arm through water, then do it through air. You will notice a big difference. Gas is much more free and energetic than liquid. That's my point. The actual size of the molecules don't change from changing states, but the different molecules in the gas form and in the liquid form are much different.

[NickE]

Originally Posted by RyanN

the different molecules in the gas form and in the liquid form are much different.

Actually, I believe that the molecules are the same. The difference is the spacing between the molecules.

[RyanN]

Originally Posted by NickE

Actually, I believe that the molecules are the same. The difference is the spacing between the molecules.

I guess that's what I'm trying to explain. Gas likes to escape faster than liquid. Liquid does not compress well while gas does.

Basically the point is that PVC should never be used to store air unless you are expecting an explosion at any time. I would never recommend using PVC. I saw what it can do, and don't want it to explode in my face. If it's a very far from anyone and inside a steel container I would then feel safe using it. Otherwise I would never use it. The kid had a failure at 40PSI while he was still charging it up to 60PSI. It was not thin pipe at all. It was very thick. It failed at a joint. It cracked the whole piece, then released the top section like a canon straight up into the ceiling. This happened at 40PSI. I know the water pressure in my home is right at 60PSI. PVC is not designed to hold air. It's not safe. It fails unexpectedly unless you drop it, and if you do that, you better run like a mad man, because it's very likely to go off. A PVC pipe with 60PSI of air, or 100PSI, or whatever is a bomb. Note that I did not use like a bomb. It is a bomb. A grenade. Unsure of when it will go off.


Hopefully I'm getting my point across. Don't use PVC for the tank. The way they're describing they're using it sounds pretty safe, but make sure no one, and I mean no one, is around it at all. There shouldn't be anyone within 100 yards of your tank when it's pressurized. Be behind the wall and don't go out unless it's not pressurized anymore.

[Bryan Herbst]

Okay, we finally got around to putting stuff together, and we are looking for tips on how to improve the cannon.

It actually has pretty decent range (shoots t-shirts about 30-40 feet), but it takes about a minute to fully pump up the tank. Now, this is pumping it to 80 PSI, but right now we are working at someone's house, not the school, so we should be able to lower the PSI and still be able to get shirts into the stands.

Currently, the barrel and tank are both made of 3 inch diameter PVC (please keep reading) and are both about 30 inches long. We are pumping the tank with two of the KOP air compressors. It takes about 1 minute and 40 seconds to pump the tank full with one compressor.

Now, as for the PVC tank- Yes, we are aware it is dangerous. However, we are limited on funds (currently have NO sponsors), and don't have many other options right now. We will be getting a different tank ASAP, but this is what we have right now. We have taken plenty of safety precautions (we stand around the corner from the tank, so if the tank explodes, it will explode into a wall and the person's lawn).


Now, if someone could suggest how to get a better pump, a better tank, or another way to do this more efficiently/effectively, we would be much obliged.

EDIT- Just remembered, and thought I would mention- We are currently using a 24v sprinkler valve hooked up to a standard FIRST control system (i.e. a 12v circuit). Would this make the solenoid open slower, and thus give us less bang per shot, or would it really not affect it at all?

[Andrew Schuetze]

take a look at our development of a similar system which has been documented here on C.D. The sprinkler valve you mention has also been discussed on C.D. and even a very nice animated graphic shows how it works. It is a relatively slow opening with a membrane that does flap during exhaust. Does your cannon honk when it shoots? Ours did.

We currently use 1 inch black pipe with npt thread for air storage as it is rated for pressurized air and is available at hardware stores. Stainless pipe is also available. One could even use a 5 gallon Craftsman air tank with only cost $20. On our system, the valve is immediately after the black pipe so that the pvc tubing and barrel do not maintain pressure except during the shot. We got better results when going to the manual ball valve but the best results are with the valve rated for this purpose. The local Parker dealer donated the valve to our team as it lists for $100.

Craftsman air tank


Ball Valve


Parker Valve

[R.C.]

We used ABS and could someone post material that is rated for a 1,000 psi. Ours works successfully, but we want to rebuild it. Also use a sprinkler valve, it works really well.

[RyanN]

We use 2 KOP compressors to charge our tank. It still takes a long time to charge from 0PSI to shooting pressure, but we can get 3 shots out of the tank before having to wait again.

We are using an old freon tank used to charge air conditioners that was empty. It's a bit large for our use, although I can't think of any other tanks that would work better.

For the sprinkler valve, we connected 3 9V batteries together in series to a relay (not a spike) and connected the relay to a spike. This gives the sprinkler valve 27V of power, which shouldn't hurt it at all (and hasn't hurt it over the past 4 years). We put a software limit on the amount of time the shooter can shoot which saves on air and charging time.

The example above me is pretty much the system we use.

[rokenboker]

team 1236 here and i have built one and it works great!


here goto this page on the site


http://www.chiefdelphi.com/forums/sh...ad.php?t=69073

[Beener]

This is what we came up with.

[Adama]

If in fact PVC is incredibly dangerous I have a few questions.

The discussion here has been only about air powered guns. Is there any greater or less danger in combustion guns? ( I'm aware that this would be disallowed on school grounds, its just a question of principle) I imagine that the lack of high pressure storage gives some what more safety though there is more of a spiking pressure affect that could counter act this.

Also on the topic of air cannons what are peoples opinions on the below link?

http://www.spudfiles.com/

I realize that it is the internet and not a well researched set of standards but one must question the danger involved if there has been a large community of people using these devices for years now. They have there share of accidents (as does any hobby such as dirt biking or snow boarding, etc) but it would seem that they only happen to people who didn't follow the well known safety practices and construction techniques established over time by the general spudding community. I guess that that if PVC were as dangerous as we are discussing then most of these people would have killed themselves by now.

[gorrilla]

Originally Posted by Adama

If in fact PVC is incredibly dangerous I have a few questions.

The discussion here has been only about air powered guns. Is there any greater or less danger in combustion guns? ( I'm aware that this would be disallowed on school grounds, its just a question of principle) I imagine that the lack of high pressure storage gives some what more safety though there is more of a spiking pressure affect that could counter act this.

Also on the topic of air cannons what are peoples opinions on the below link?

http://www.spudfiles.com/

I realize that it is the internet and not a well researched set of standards but one must question the danger involved if there has been a large community of people using these devices for years now. They have there share of accidents (as does any hobby such as dirt biking or snow boarding, etc) but it would seem that they only happen to people who didn't follow the well known safety practices and construction techniques established over time by the general spudding community. I guess that that if PVC were as dangerous as we are discussing then most of these people would have killed themselves by now.

I would definately say thats a combustion gun would be even more dangerous

PVC SHOULD NOT to be used EVER for anything being pressurised except for WATER and this should be the end of it(unfortunately it most likely wont )

and on the topic of alot of people using PVC, I belive there just asking for it, but its thier decision
Ill' give you that PVC dosent ALWAYS explode(which is why alot of people use it) but IF it does,someone COULD be seriously hurt, I dont know about you guys, but I would rather not risk having someone else injured because of me

I also belive this has been said before MANY MANY times by far more experience people than me