The cement and primer had dried for 2 days before firing. Here are pictures of the elbows and cannon.
Spud gun exploding
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.
The cement and primer had dried for 2 days before firing. Here are pictures of the elbows and cannon.
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jackssmirkingrevenge
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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:
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:
hectmarr wrote:You have to make many weapons, because this field is long and short life
Lucky you were unharmed. 
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farcticox1
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Don't forget if that was regular PVC it's not rated for air pressure.
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Moonbogg
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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.
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D_Hall
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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.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:)
(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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jackssmirkingrevenge
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Perhaps if such a big bore is required, perhaps you should consider a coaxial design.Djkitten wrote:Since I couldn’t find any solenoids larger than 1 inch, I can’t really change them to a larger size.
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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jackssmirkingrevenge
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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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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.
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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Good find, I don't know enough about standard fittings to tell if it will scale up to OP's larger caliber requirements.Moonbogg wrote:Here is the video showing how to make the piston.
[youtube][/youtube]
hectmarr wrote:You have to make many weapons, because this field is long and short life