2 Inch QEV Cannon

[jackssmirkingrevenge]

For some reason I expected the tree to collapse

Be careful with PVC in colder weather, it tends to get brittle as the temperature drops.

[Jamzearljones]

Be careful with PVC in colder weather, it tends to get brittle as the temperature drops.

I’m not sure if I should admit this... but it wasn’t actually that cold. Maybe mid 40’s (°F) Those boots were just so comfy!... and close to the door. We did have a constant breeze that wasn’t too strong, but it just felt like it cut right through you.

So...actual: 45°F, feels like: DEATH

However! I still appreciate the warning. I hadn’t thought of the cold affecting the PVC. I guess it was lucky that the compressor we used only went up to 100psi. Has anyone wrapped their PVC cannons in anything to prevent shrapnel if, in the worst case scenario, something does rupture? I have seen some pretty serious injuries from PVC and I am under no illusions that what I am holding is anything other than a disaster in the wrong conditions. One of my biggest fears is dropping the thing when it’s charged.
Finally, where should I go from here? Looking for a gentle nudge, I’ll try to do my own research once I’ve got a direction to run. PVC seems to be the limiting factor now. I don’t really want to venture into the 6” PVC range because the pressure ratings drop off too much for my liking, not to mention the fittings are stupid expensive. I would be more inclined to work with metal pipe, higher pressure for the $$$. The QEV I am using is only rated to 125psi (though I regularly use it at 145psi). I will be one unhappy camper if I ever find it’s failure point; I found the replacement diaphragm kits run right around $65 (USD). I would need to use some other form of valve if I want to get past that limitation. I am still looking to remain pneumatic, but nothing is set in stone right now.

[farcticox1]

[youtube][/youtube]

[Jamzearljones]

I would like to see that freezer test done from 6”, 12”, 24”, etc...

[farcticox1]

And he's using 140psi, that's about what I use. I would not go any higher.

[Air2theBrain]

Enjoyed that footage, PVC takes a hell of a beating that's for sure.

I bought some high pressure rated pvc yesterday..more expensive than brass fittings.

Hope they handle more than 140psi..

[jackssmirkingrevenge]

I’m not sure if I should admit this... but it wasn’t actually that cold. Maybe mid 40’s (°F) Those boots were just so comfy!... and close to the door. We did have a constant breeze that wasn’t too strong, but it just felt like it cut right through you.

So...actual: 45°F, feels like: DEATH

The clothing definitely threw me off, but nothing wrong with wanting to be comfortable

Finally, where should I go from here? Looking for a gentle nudge, I’ll try to do my own research once I’ve got a direction to run. PVC seems to be the limiting factor now. I don’t really want to venture into the 6” PVC range because the pressure ratings drop off too much for my liking, not to mention the fittings are stupid expensive. I would be more inclined to work with metal pipe, higher pressure for the $$$. The QEV I am using is only rated to 125psi (though I regularly use it at 145psi). I will be one unhappy camper if I ever find it’s failure point; I found the replacement diaphragm kits run right around $65 (USD). I would need to use some other form of valve if I want to get past that limitation. I am still looking to remain pneumatic, but nothing is set in stone right now.

If you want to stay pneumatic, higher pressure is definitely the way to go. For a given amount of air, a smaller chamber at higher pressure will give you more power.

Something I always link to that illustrates the point, here is the data for a virtual launcher modeled in GGDT with a progressively smaller chamber filled to a higher pressure - in each case, we're talking about the same quantity of air, but in a reduced volume and therefore at higher pressure.

20 inch chamber at 50 psi - 406 feet per second - 2 ft lbs

10 inch chamber at 100 psi - 537 feet per second - 3 ft lbs

5 inch chamber at 200 psi - 684 feet per second - 6 ft lbs

2.5 inch chamber at 400 psi - 830 feet per second - 8 ft lbs

1.25 inch chamber at 800 psi - 958 feet per second - 11 ft lbs

0.625 inch chamber at 1600 psi - 1006 feet per second - 12 ft lbs

It's not difficult to see why, if you have higher pressure in the chamber it's going to cause a more rapid pressure spike in the barrel behind the projectile and this impulse is what gives the projectile its energy.

You're definitely going to have to invest substantially in materials if you want to go the pneumatic big-bore route safely with higher pressures though, and will likely have to make your own valves.

If pure power is desired for minimal financial outlay and using existing fittings, a burst disk valve is an option work looking into. Some basics in the wiki article: http://www.spudfiles.com/spud_wiki/index.php/Burst_disk