Most Powerful FIRST Team created T-Shirt Cannon

[JohnFogarty]

Yeah Team 1102 believes we've created the best. Over 1 football field shot at our relay for life event.
http://www.youtube.com/watch?v=VbYJoCPbZ1Y
http://www.youtube.com/watch?v=lt7GJ6_8dY4

[NickE]

Nice shots but I don't think I'd want to be near it when pressurized.

PVC really shouldn't be used to store compressed air. In short, pressure rated PVC is not rated to hold compressible gas and can fail violently when holding compressed air. See these threads for more information:
http://www.chiefdelphi.com/forums/sh...ad.php?t=75929
http://www.chiefdelphi.com/forums/sh...ad.php?t=77871

[JohnFogarty]

I think we're ok...3inch 350psi PVC and we never go above 100psi that shot was at 80psi. Plus the mentor who built it with us he made the gun, is plastic engineer/machine specialist he would know a bit more about this that most people. Plus we have members of our team who create 1000psi potato guns with PVC.

[JohnFogarty]

http://www.engineeringtoolbox.com/pv...res-d_796.html
Please do your reasearch we did this is "AIR" tests

[Chris is me]

Originally Posted by John_1102

I think we're ok...3inch 350psi PVC and we never go above 100psi that shot was at 80psi. Plus the mentor who built it with us he made the gun, is plastic engineer/machine specialist he would know a bit more about this that most people. Plus we have members of our team who create 1000psi potato guns with PVC.

PVC is not rated for air pressure, only liquid pressure. PVC can catastrophically fail at 80PSI, causing serious injury.

Originally Posted by John_1102

http://www.engineeringtoolbox.com/pv...res-d_796.html
Please do your reasearch we did this is "AIR" tests

Those aren't air tests. Those are liquid tests. "Please do your research".

[Jack Jones]

More research:

[JohnFogarty]

Correct me now if i'm wrong cause I did the right homework on ABS pipe. Safe or no?

[MrForbes]

PVC is NOT safe with compressed air....please don't use your cannon until you replace the pipe with something more suitable for use with compressed air.

ABS appears to be not as dangerous.

[JohnFogarty]

I'm not seeing this happen?? I have a special program protocol I put into my inventor. I have tried 3" Shcedule 40 and 80, with an air pressure simulation. using FIRST regulators and compressors. and the couplings we primed and had machined. The castostophic failure doesnt occur because the REG is INPUT 150psi OUTPUT only 50psi. we must have done almost 300-400 shots last night. Doing the reashearch on how the system we use flows air, the equalibrium is maintained everywhere. The back of the cannon has a dump tank which in a sense also has a quick disconnect. the cannon barrel is the same design used in most launchers never seen to fail..the barrel. Now i CAN SEE NOW THAT THE ACCUMULATORS WE MADE are possibly dangerous 2 1.5 foot long 3 inch pressure rated 370psi capped and primed with..intresingly a air PVC cap. ABS seems to no safer. only one type Air-Line Xtra is...and it's not sold anywhere. I forwarded this to our mentor and he said maybe aluminum, but we have homework to do because dual layered 3in shedule 40 layer with 4in sechudule 40 doesnt rupture unless you are at an air pressure of 1500psi...two of our members made a nailgun with these specifications.

[Ian Curtis]

Originally Posted by Chris is me

PVC is not rated for air pressure, only liquid pressure. PVC can catastrophically fail at 80PSI, causing serious injury.

Those aren't air tests. Those are liquid tests. "Please do your research".

What is the difference between gas pressure and liquid pressure? If they are both Force/Area, how do they make the material fail in one case, and not in the other? Does it have something to do with the rate of expansion of a gas vs. a liquid?

Does it specify that they are liquid tests, or does everyone in the thermoplastics business just know that gas pressure is not liquid pressure?

I don't want air cannons blowing up in my face.

[NickE]

Originally Posted by iCurtis

What is the difference between gas pressure and liquid pressure? If they are both Force/Area, how do they make the material fail in one case, and not in the other? Does it have something to do with the rate of expansion of a gas vs. a liquid?

From another thread:

Originally Posted by Daniel_LaFleur

Lets consider PVCs pressure rating for a moment. PVC is only pressure rated for liquids (and for a very good reason):
Water is incompressable, much like a steel block ... if you push down on a steel block with 50 PSI it will not compress and if you release that force instantly the steel block will not move.
Air, on the other, hand is compressable, like a 50 pound spring. Apply 50 psi to it and the sprin compresses. release that force instantly and the spring not only goes back to it's original shape but rockets off of the surface it was on.

[Hawiian Cadder]

what i usually do is put the PVC tube inside a cardboard packaging tube, it adds strength and then even if the PVC ruptures, the cardboard prevents it from creating shrapnel.

[Chris is me]

Originally Posted by John_1102

I'm not seeing this happen?? I have a special program protocol I put into my inventor. I have tried 3" Shcedule 40 and 80, with an air pressure simulation. using FIRST regulators and compressors. and the couplings we primed and had machined. The castostophic failure doesnt occur because the REG is INPUT 150psi OUTPUT only 50psi.

The PSI doesn't matter. PVC can catastrophically fail without warning.

We must have done almost 300-400 shots last night. Doing the reashearch on how the system we use flows air, the equalibrium is maintained everywhere.

Unfortunately, PVC fails without warning. It could be the first shot, or the 1,000th shot, or never.

I forwarded this to our mentor and he said maybe aluminum, but we have homework to do because dual layered 3in shedule 40 layer with 4in sechudule 40 doesnt rupture unless you are at an air pressure of 1500psi...two of our members made a nailgun with these specifications.

Again, not air pressure, water pressure. Compressed air is different.

If you use aluminum and it ruptures, air will leak out, but it won't explode into tiny little pieces of shrapnel. PVC will.

[JohnFogarty]

Lets consider PVCs pressure rating for a moment. PVC is only pressure rated for liquids (and for a very good reason):
Water is incompressable, much like a steel block ... if you push down on a steel block with 50 PSI it will not compress and if you release that force instantly the steel block will not move.
Air, on the other, hand is compressable, like a 50 pound spring. Apply 50 psi to it and the sprin compresses. release that force instantly and the spring not only goes back to it's original shape but rockets off of the surface it was on.????

Umm Yeah the principle of compressing water has to happen other wise when you put your finger over the end of a hose nothing would happen. Water is compressable. 1000psi water jets are used to cut steel.....so again logic isn't following here. It's compressable to a very very small degree.

[sdcantrell56]

Originally Posted by John_1102

Umm Yeah the principle of compressing water has to happen other wise when you put your finger over the end of a hose nothing would happen. Water is compressable. 1000psi water jets are used to cut steel.....so again logic isn't following here. It's compressable to a very very small degree.

Water is most definitely incompressible. Just wait till you have some fluids classes.

If you're using this thing around other people that surely don't understand the risk use something else to store the pressurized air.