Spud gun exploding

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Djkitten
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Sun Nov 17, 2019 7:49 pm

Hi, I’m a new member to the site and since my spud gun exploded when I fired it, I’m wondering why it exploded. I was shooting water filled halfway in the barrel at 90 psi. The cannon was Mede if 3 inch pressure rated pipe along with a 1 inch solenoid 2 couplings to step 3” to 2” then to 1”, then there was some 1” pvc for the female to female joints, and 2 couplings. All pressure rated and fixed with primer and pvc cement. I am completely open to suggestions. The barrel and air reservoir are both 5’ and 3” diameter. The cannon popped at the 2 elbow joints connection to the cannon neither the barrel or air reservoir was damaged.
The cement and primer had dried for 2 days before firing. Here are pictures of the elbows and cannon.
F0495421-FB50-4C64-9970-C0BEDB8BD50E.jpeg
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jrrdw
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Mon Nov 18, 2019 6:04 am

Your barrel was all clogged up and once fired the air had to go some where, out the weakest points. Live and learn...

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jackssmirkingrevenge
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Mon Nov 18, 2019 7:01 am

Welcome to the forum and glad you survived your first spudgun incident!

Water is heavy, so trying to launch it is going to give you significant recoil. The joint that broke is the weak point in your circuit so it's almost not surprising that it broke.

Typically you'd want to attach the barrel to the chamber somehow in this configuration in order to remove the stress from that joint, something like this using a wooden spacer and a hose clamp:

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hectmarr wrote:You have to make many weapons, because this field is long and short life
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hectmarr
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Mon Nov 18, 2019 9:34 am

Uffff ... I don't even want to think about what would happen if a catastrophic failure occurs 4 inches from my face and with 8X ... :? Lucky you were unharmed. :)
Ideas don't make holes. The weapons yes! ;)
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farcticox1
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Mon Nov 18, 2019 6:31 pm

Don't forget if that was regular PVC it's not rated for air pressure.
Djkitten
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Mon Nov 18, 2019 8:44 pm

It is all pressure rated. Also thanks for the tip the only thing I have to replace are the elbows, I will made one those spacers soon! Thank you for the suggestions:)
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Moonbogg
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Tue Nov 19, 2019 2:10 am

I'm with JSR on this one. The recoil appears to be the main culprit from where I stand. I'd expect that little elbow to break if it's absorbing the recoil from a barrel full of water. I'd use a larger elbow and support the barrel so that it can't move up or down, nor back and forth.
Djkitten
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Tue Nov 19, 2019 8:44 am

Since I couldn’t find any solenoids larger than 1 inch, I can’t really change them to a larger size.
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D_Hall
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Thu Nov 21, 2019 10:04 pm

Djkitten wrote:It is all pressure rated. Also thanks for the tip the only thing I have to replace are the elbows, I will made one those spacers soon! Thank you for the suggestions:)
In the spud gun world a lot of newbs seem incredulous when you comment on the choice of PVC. "It is all pressure rated" is a common response. It is also a naive response. Pressure rated for liquids is not the same thing as pressure rated for gases. PVC is pressure rated for liquids. It is NOT pressure rated for gases. Can you use it for gases? Yes.... But you must also be a lot more careful about how you do things and understand that you are NOT using the items as they were designed to be used. In other words, PVC is NOT rated for spud gun use. Act accordingly.

(And for some of us, "act accordingly" means we never use PVC.)

Oh, and sign me up as another who thinks unsupported recoil was the problem here.
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D_Hall
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Thu Nov 21, 2019 10:05 pm

Djkitten wrote:Since I couldn’t find any solenoids larger than 1 inch, I can’t really change them to a larger size.
You didn't look very hard. They're spendy, but they're out there. Search for "commercial irrigation valve".
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jackssmirkingrevenge
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Fri Nov 22, 2019 9:01 am

Djkitten wrote:Since I couldn’t find any solenoids larger than 1 inch, I can’t really change them to a larger size.
Perhaps if such a big bore is required, perhaps you should consider a coaxial design.

It will requite a modicum of fabrication, as opposed to putting together standard parts, but it's doable and has the potential for a lot more performance in a stronger design. If anything, greater flow will allow you to achieve the same results with lower pressure.

The bigger question therefore is "what are you trying to shoot, and how fast?"
hectmarr wrote:You have to make many weapons, because this field is long and short life
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Moonbogg
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Fri Nov 22, 2019 10:50 am

Why not a piston design? They can be done pretty simply and they destroy the sprinkler valve cannons, don't they?
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jackssmirkingrevenge
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Fri Nov 22, 2019 11:51 am

That's where the fabrication comes in, you're not going to find a ready-made piston at home depot, but with a bit of imagination and, dare I say, epoxy, all is possible ;)
hectmarr wrote:You have to make many weapons, because this field is long and short life
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Moonbogg
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Fri Nov 22, 2019 6:00 pm

Look at this one this guy made. It's great and super simple. Probably the simplest piston cannon I've seen and works fantastic. He said it can be done without tools, a nd yep, that piston requires no tools. I just watched. This is a great design I think. I suggest the OP check this out and ditch the sprinkler valve designs.

Here is the video showing how to make the cannon.


Here is the video showing how to make the piston.
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jackssmirkingrevenge
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Sat Nov 23, 2019 7:35 am

Moonbogg wrote:Here is the video showing how to make the piston.

[youtube][/youtube]
Good find, I don't know enough about standard fittings to tell if it will scale up to OP's larger caliber requirements.
hectmarr wrote:You have to make many weapons, because this field is long and short life
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