Rate my cannon

Show us your pneumatic spud gun! Discuss pneumatic (compressed gas) powered potato guns and related accessories. Valve types, actuation, pipe, materials, fittings, compressors, safety, gas choices, and more.
rookie builder
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Sat Jul 17, 2021 11:19 pm

I've been interested in building air cannons for a long time but I only recently discovered this site. I just finished building a cannon I think is pretty powerful. It uses an angle seat valve and has a max rated pressure of 300 psi (I've tested it up to 500 psi). I use a 3/2 way solenoid valve to open and close the angle seat valve. I shot a pvc end cap from it once and I heard a sound that was like a whip crack. I think that was a sonic boom. Next time I test the cannon I'll record everything with my phone so you can see how it works visually.
a picture of the cannon
a picture of the cannon
Other random info:

Angle seat valve:
14Cv, rated valve pressure 300 psi, rated piston pressure 150 psi

Main air chamber:
2 inch x 10 inch schedule 80 pvc, rated pressure 400 psi

3/2 way solenoid valve:
12V DC, 6.7Cv, rated pressure 4.0 MPa, response time 0.04-0.08 seconds

Batteries:
4x 1200mah 18650 lithium ion batteries, 3.7V

PVC primer and cement:
Weld On P-68 primer, Oatey Heavy Duty Gray Cement

Thread sealant:
PTFE tape, Loctite 242
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farcticox1
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Sun Jul 18, 2021 6:45 am

I like it, 500psi is a lot for PVC though :o
rookie builder
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Sun Jul 18, 2021 7:19 am

farcticox1 wrote:
Sun Jul 18, 2021 6:45 am
I like it, 500psi is a lot for PVC though :o
Well the schedule 80 pvc I'm using is rated for 400 psi and the burst pressure is usually 3-4 times higher than the rated pressure so I should be fine.
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mark.f
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Sun Jul 18, 2021 7:52 pm

Neat valve. I'd like some more details but I'm with @farticox1, that's a lot of pressure for PVC.
But even with all of that, I think what would worry me more is if there was no balance tap on that battery pack you wired up. :D
rookie builder
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Sun Jul 18, 2021 8:52 pm

What is a balance tap?
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mark.f
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Tue Jul 20, 2021 8:42 am

rookie builder wrote:
Sun Jul 18, 2021 8:52 pm
What is a balance tap?
It's just lead connected between the two cells for your charger to connect to to keep the voltages equal when charging (and discharging too if you use a battery management system, homemade or otherwise).
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Moonbogg
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Tue Jul 20, 2021 5:32 pm

Nice cannon. You're taking a significant risk by using PVC with that much pressure inside. It can fail within it's rated pressure for no apparent reason because it's plastic and it tends to be fragile. It won't just crack, split or tear, but it will fragment and explode in your face. Wear safety goggles, a safety T-shirt, and a bomb suit. Operate remotely from the safety of an underground bunker (nuclear rated only).
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farcticox1
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Wed Jul 21, 2021 4:35 am

rookie builder wrote:
Sun Jul 18, 2021 7:19 am
farcticox1 wrote:
Sun Jul 18, 2021 6:45 am
I like it, 500psi is a lot for PVC though :o
Well the schedule 80 pvc I'm using is rated for 400 psi and the burst pressure is usually 3-4 times higher than the rated pressure so I should be fine.
That's hydrostatic rating, it's not even rated for gas pressure, steel is the way to go. I have done it myself to test stuff but have replaced it all now with steel pipe.
pvc-warning.jpg
IpexUSA_036382.jpg
It's actually illegal in some places for this reason, https://www.tssa.org/en/boilers-pressur ... sb00_8.pdf

We have had 2" sch40 water lines fail where I work at 60psi because of age and hammer.
rookie builder
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Fri Jul 23, 2021 4:42 am

update:

Some test shots with pvc end caps against apples

https://www.youtube.com/watch?v=N6xgj2vuL9E&t=4s
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mark.f
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Fri Jul 23, 2021 6:27 am

Interesting, just out of curiosity, have you thought about modifying the angle seat valve to be outlet-sealing like this? (He made it out of a wye strainer though).
rookie builder
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Fri Jul 23, 2021 8:37 pm

mark.f wrote:
Fri Jul 23, 2021 6:27 am
Interesting, just out of curiosity, have you thought about modifying the angle seat valve to be outlet-sealing like this? (He made it out of a wye strainer though).
I don't like the idea of modifying something compact and complicated like that angle seat valve I bought. Especially since I'm using it for high pressure applications
wafen
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Tue Jul 27, 2021 9:59 am

A cool idea,and I have to say angle seat valve is excellent.
I have made sth similar https://www.spudfiles.com/viewtopic.ph ... 49#p387349
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