PVC Primer/Glue says DO NOT TEST WITH AIR

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.
Luke31
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Wed Oct 28, 2020 7:19 pm

When I saw it on the back of the can, I wasn't sure what to make of it since so many people online were building air cannons using PVC. There are charts online that list the pressure rating for different pipe sizes. So I make sure to stay below those ranges.

But if the manufacturer themselves are putting in bold letters on the back to not test it with air, maybe using PVC in the first place was wrong after all.

This article warns of air pressures even going over 6 psi
https://www.charlottepipe.com/Documents ... ystems.pdf

Google search has nothing good to say about pvc and air
https://rb.gy/3vp7tc

Is schedule 80 even safe to use?

Kind of throws a wrench into my plans since I wanted to build many air cannons in order to test different setups. I will probably build my final design using metal.
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mrfoo
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Thu Oct 29, 2020 1:27 am

PVC primer and cement are solvents. They physically attack the surface of the pipe and fittings, and can produce weak spots exactly where you don't want them.

PVC pressure rating charts give the rated pressure for constant pressure conditions, with the pipe properly supported, and without pressure surges.

As mentioned in the article you link, air is compressible and stores lots of energy. If a pipe fails with air, all that energy has to go somewhere. Water is largely incompressible and stores a very low amount of energy. If a pipe fails with water, a tiny amount piddles out and the pressure is all gone.

As to whether you should use PVC, it's your call.
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Moonbogg
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Sat Oct 31, 2020 3:32 pm

There is a modeling program we use called GGDT. It can reduce the burden of trying to do all sorts of MATH and will allow you to just design your cannon. I don't have the link on hand, but it's around here somewhere. There is a similar program called HGDT used for combustion cannons. I used the program to model the performance of my cannons before building them and the program's predictions were impressively close to the real performance. That way, you don't have to spend time and money making a bunch of PVC cannons that will just end up in the trash anyway.
Luke31
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Sun Nov 01, 2020 9:53 pm

Moonbogg wrote:
Sat Oct 31, 2020 3:32 pm
There is a modeling program we use called GGDT. It can reduce the burden of trying to do all sorts of MATH and will allow you to just design your cannon. I don't have the link on hand, but it's around here somewhere. There is a similar program called HGDT used for combustion cannons. I used the program to model the performance of my cannons before building them and the program's predictions were impressively close to the real performance. That way, you don't have to spend time and money making a bunch of PVC cannons that will just end up in the trash anyway.
Do you know what the programs called? Something like that would really help me out.
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Moonbogg
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Sun Nov 01, 2020 11:39 pm

Go to the thread below and scroll down a bit. Click the zip file for GGDT. It stands for Gas Gun Design Tool. The other one is HGDT (Hybrid Gun Design Tool). Hybrid's are pressurized propane and air cannons and are a different beast altogether. Anyway, get familiar with GGDT and entering inputs for your design. The performance modeling is very good. D Hall developed these and they've been vital for the serious spud gunner for modeling performance and optimizing the design.

viewtopic.php?f=6&t=26950
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jackssmirkingrevenge
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Wed Nov 04, 2020 10:06 am

hectmarr wrote:You have to make many weapons, because this field is long and short life
Luke31
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Sun Nov 08, 2020 2:07 am

Moonbogg wrote:
Sun Nov 01, 2020 11:39 pm
Go to the thread below and scroll down a bit. Click the zip file for GGDT. It stands for Gas Gun Design Tool. The other one is HGDT (Hybrid Gun Design Tool). Hybrid's are pressurized propane and air cannons and are a different beast altogether. Anyway, get familiar with GGDT and entering inputs for your design. The performance modeling is very good. D Hall developed these and they've been vital for the serious spud gunner for modeling performance and optimizing the design.

viewtopic.php?f=6&t=26950
I looked at the GGDT program and it doesn't appear to have an option to calculate the maximum range in which it will be able to fire which is in my opinion the whole point of the software..

There's no option to adjust the angle of the barrel either.
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Sun Nov 08, 2020 3:56 am

There is an external ballistics calculator in GGDT in which you can either choose to use a specific barrel angle, or calculate the angle for maximum range. You can also enter the coefficient of drag.
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Sun Nov 08, 2020 3:58 pm

Luke31 wrote:
Sun Nov 08, 2020 2:07 am
I looked at the GGDT program and it doesn't appear to have an option to calculate the maximum range in which it will be able to fire which is in my opinion the whole point of the software..
The point of the program is to have an idea of what your muzzle velocity will be. As for maximum range, that will depend heavily upon everything from the weather to the shape of your projectile. As Moondog said, there's a (crude) external ballistics calculator built in, but external ballistics are pretty trivial to calculate compared to internal ballistics.

All that said... Earlier in the thread there was the question about the wisdom of building cannons with PVC. Make no mistake.... Building cannons with PVC is something that should be reserved for (a) very weak cannons (ie, toys where the builder isn't too concerned about power), or (b) idiots who want to end up as viral videos that everyone else can laugh at.
Simulation geek (GGDT / HGDT) and designer of Vera.
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