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".

[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.

[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.

[JohnFogarty]

I may end up making my half inch thick lexan boxes after all, We probably won't be able to replace the PVC but i'm going to install bulletproof box around them for saftey. The dump tank on the gun however i'm not sure yet.
http://maikenmagic.com/?ref=gallery&...irt%20Launcher

[Jack Jones]

A good way to win the Darwin Award?

.

[will_1359]

lol i'm sure the boys doing the t-shirt cannon for team 1359 will take this as a challenge.

right now our most powerful launch we've had was using a 3 foot x 4in(i don't feel like getting the cubic inches) air reservoir(yes it was PvC, but it was the highest rated pressurized PvP we could find, what we're worried about blowing are the seals holding everything together), pumped to 125psi. It may have actually traveled further then a football field lol, might have to try it again.

only downside is that we havn't set up the robot to fire it yet, it's all hand operated.

[joek]

a 5-gal 150 psi rated air tank is like $30 at northern tool
it's what we use for ours, and you only want to go to 60 psi, otherwise the shirts go too far

[gblake]

Originally Posted by sdcantrell56

Water is most definitely incompressible.

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.

You are both mistaken.

SDCantrell - Water will compress when you press upon it, just like every ordinary real material will. However, as John said, it compresses very little, and for that reason pretending it is incompressible is a useful approximation.

John - Water's compression has nothing (or at least very little) to do with whether a 1000psi waterjet can cut something. That pressurized water will fly out of a nozzle and cut things is a separate topic from how much or how little it's volume changes when it is put under pressure.

Blake