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PVC Detonation Protection

A place to ask general spud cannon related questions.
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PVC Detonation Protection

Unread postAuthor: turbohacker » Sun Dec 09, 2007 4:17 pm

I have not been active in the forums for quite some time now because, as you may remember, my father was in an acident regarding pneumatic spud cannons which ultimately caused him to loose his left eye.

I would now like to start making cannons again. I need to make sure that they are completely explosion proof. This post is dedicated to any ideas regarding safety for pneumatic cannons.

My ultimate goal is to have a cannon that, if somehow destroyed, will have no possible chance of sending PVC fragments anywhere.

My initial idea was a fabric sleave of some kind to be used over the chainber to contain any PVC fragments in the event of an explosion. Do you think this would work? Any other ideas?

Baselines: Cannon is made of sched 40 PVC Pressure is 120PSI
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Unread postAuthor: MrCrowley » Sun Dec 09, 2007 4:43 pm

Don't use CO2...

If your only using 120psi you'll be fine without any protection just as long as your wearing clothes, a sweatshirt would help. So with that said a fabric sleeve of some sort that doesn't rip easily should do the job, it wont contain the blast but it will slow down the already slow fragments.

When I had PVC blow at 110psi, me and two others didn't get hurt at all, that was point blank range, though it could've done damage to our eyes, so if you wear glasses as well you should be fine.
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Unread postAuthor: mopherman » Sun Dec 09, 2007 4:44 pm

I would make an outer shell for the chamber to catch any fragments. OR, this might sound crazy, use metal.
EDIT: I dont mean to sound like a smartass.
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Unread postAuthor: turbohacker » Sun Dec 09, 2007 4:47 pm

I have build many metal guns, however PVC is faster, cheaper, and easyer to work with.

These guns will be used by primarily kids (as snow shooters) and will have pop off valves. This safety precautioin is in case one is dropped.
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Unread postAuthor: mopherman » Sun Dec 09, 2007 4:49 pm

In the case of snow shooters, NEVER use pvc. It becomes brittle when cold and could risk another explosion.
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Unread postAuthor: Ragnarok » Sun Dec 09, 2007 5:21 pm

Well, the easiest solution to avoiding PVC fragments is to not use PVC.

I believe there were a series of experiments a while back that proved that external protection around the chamber was fairly useless, and often just added extra debris to be thrown.
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Unread postAuthor: DYI » Sun Dec 09, 2007 5:21 pm

First, if its for use in the winter you need a built in liquid heating system, set to the right temperature. After that, a few wraps of carbon fiber, done properly, should stop, or at least slow down shrapnel. A more cost effective and simpler choice would be to simply use steel pipe. You do live in the US, can't you get it from Mcmaster?
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Unread postAuthor: hi » Sun Dec 09, 2007 5:34 pm

simple, dont use it. make them out of metal pipe, it has a much lower chance of failing.
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Unread postAuthor: frankrede » Sun Dec 09, 2007 9:12 pm

PVC PIPE IS NOT MEANT FOR USE WITH PRESSURIZED AIR FOR A REASON.
Its like building tall buildings out of cheap materials
Can it be done? Yes.
But will it hold up? probably not.



Also, instead of using a pop off valve with low flow, a good idea would be to use a union with a burst disk that blows at a certain pressure in the event you might have a malfunction and your reg goes out.
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Unread postAuthor: SpudBlaster15 » Sun Dec 09, 2007 9:26 pm

Air pressure vessels made with PVC will withstand air pressure just as well as they will water pressure.

The key to avoiding damage to human tissue caused by PVC shrapnel is to avoid creating shrapnel in the first place. Use the pipe within its pressure rating, and do not subject it to shock (ESPECIALLY when the pipe is pressurized, and it's temperature is below ~5*C or so) or prolonged doses of UV radiation. If you are using a regulated high pressure source, install a pop-off valve to prevent over pressurization in the event of regulator failure.

Should these precautions be taken, there should be no reason to fear an explosion, and the resultant shrapnel.
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Unread postAuthor: Thursto » Sun Dec 09, 2007 9:29 pm

Hey, sad to hear about your dad but about the topi, if i were me, i'd use very high strong pressure rated PVC, and for an outer shell make it out of ABS (because it tears) or just more strong pvc, and have like a 1cm gap between the chamber and the shell, i'd drill holes in the shell, that way if it explodes it doesn't put the shell under pressure, the escaping air can go threw the holes in the shell, and all the shell does is hold back the pvc fragments. Well that is just my idea, another one could be fill the shell with that expandable foam crap. Anyways hope you figure something out for it, cant wait to see it!

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Unread postAuthor: MrCrowley » Sun Dec 09, 2007 9:46 pm

frankrede wrote:PVC PIPE IS NOT MEANT FOR USE WITH PRESSURIZED AIR FOR A REASON.
Its like building tall buildings out of cheap materials
Can it be done? Yes.
But will it hold up? probably not.


Chances are it will hold, but if it doesn't they will get sued.

The reason they don't recommend PVC with compressed air is because it causes a lot more shrapnel then if it was high pressure water, like SB15 said, if it can hold high pressure water it can hold high pressure air (up to it's rating of course).

But if the pipe fails for a manufacture reason and it's used with compressed air, someone could loose an eye and they could try and sue the pipe company saying the pipe failed lower then the rating.
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Unread postAuthor: rna_duelers » Sun Dec 09, 2007 10:04 pm

Warp it in Kevlar,yes it's costly and would take a long time to get it perfect but it is also very strong.

I have also had pressure rated pipe go pop on me,it was about 10cm from my face and I wasn't hurt at all,sure it was loud and shook me up a bit but no pieces of PVC in my skin.You could possibly make small section that are covered with sheet metal as a barrier and if it does rupture the pieces will be stoped by the sheet metal.I don't mean cover the whole thing in sheet metal just certain areas of the cannon around your neck,face,groin etc,cover the important ones.Wear a paintball mask when spudding if you want to be cautious.
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Unread postAuthor: Infernal Maveric » Mon Dec 10, 2007 4:44 am

You stated that the cannon/s will be made for use in the winter snow by children. PVC and cold do NOT mix, and more importantly so, PVC fragments, children, and angry parents are not a fun mix.

Use metal for the whole gun. It will be safe to use in the cold (with gloves on) and won't explode in your face.
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Unread postAuthor: SPG » Mon Dec 10, 2007 6:58 am

Thursto wrote:if i were me, i'd use very high strong pressure rated PVC, and for an outer shell make it out of ABS (because it tears) or just more strong pvc, and have like a 1cm gap between the chamber and the shell, i'd drill holes in the shell, that way if it explodes it doesn't put the shell under pressure, the escaping air can go threw the holes in the shell, and all the shell does is hold back the pvc fragments. ~ Thursto


I reckon that's a very good idea, and much better than wrapping it tightly in anything. I doubt PVC shards will accelerate that much in half an inch or so, so would be unlikely to break the outer pipe. What you do need though is to make sure that the air can get through it as efficiently as possible so the pressure is released.

I've always wondered with spudguns about building in controlled failure points (a burst disc is an example of one of these). As a for instance, if you put a T between chamber and valve you could then use a modified end cap to hold a burst disc in place in the side exit of the T. Over pressurise and that provides your controlled failure.
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