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Alternatives to PVC?

A place to ask general spud cannon related questions.
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Alternatives to PVC?

Unread postAuthor: oldchris » Sun Mar 22, 2009 11:04 am

AFAICT, PVC us only used for non-pressure rated applications hereabouts (Ontario): central vac pipes, furnace intake/exhaust, underground drainage, electrical conduit etc.

We do still seem to use CPVC for potable water, but pretty much only in 1/2 and 3/4 nominal - and PEX seems to be taking over this application. Larger sizes of ABS DVW pipe is readily available. Strangely enough, you can buy PVC fittings in large sizes, but no pipe.

Just how unsafe is ABS for pressure vessels, combustion chambers, etc? Are there any other easily obtained materials than could be substituted? I have seen Cu pipe in larger sizes, but I would think this would move anything constructed from it into the "semi-portable" category!

TIA,
Chris
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Unread postAuthor: Demon » Sun Mar 22, 2009 11:29 am

The problem in pvc is that it fails "explosively", sending sharp pvc pieces evrywhere.

The abs is not pressure rated ( you can get some tough but it costs a lot )
but when it fails ,it liberate the pressure, but dont send pieces evrywhere.

Sch80 abs would be an alternative of pvc ( but not for the price ).

( i am canadian too )
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Unread postAuthor: TurboSuper » Sun Mar 22, 2009 12:33 pm

I find that galvanized steel and copper are readily available in Canada. They don't come in good sizes for combustions, but for pneumatics it's golden stuff. It's expensive, but given the right valve you could take your cannon to several hundred PSI.
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Unread postAuthor: starman » Sun Mar 22, 2009 12:41 pm

Demon wrote:The problem in pvc is that it fails "explosively", sending sharp pvc pieces evrywhere.


As many times as I've heard this, I've never seen it happen or heard of it happening to sched 40 or better PVC. Yes, clean-outs fly off, chamber/barrel transitions have cracked, barrels have cracked off into a hand full of pieces, 180 degree rear over and under chamber to barrel piping has cracked and/or broken loose...yes....I've seen that. However, not the thousands of glass-like shards traveling at explosive speeds ripping to shreds everything in its path....that's the image that is portrayed.

The handful of "explosive" videos I've seen were either faked or not sched 40 pipe and while I'm sure it scared the daylights out of the shooter, was far from lethal....eye injury or minor cuts and abrasions really the only possibility here...

I don't want to down play the dangerous possibility of someone abusing the material with pneumatic over pressures (pressures beyond rating) or hybrid mixes, especially over 2x...a big no-no.

Show me the evidence...
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Unread postAuthor: frankrede » Sun Mar 22, 2009 1:11 pm

starman wrote:
Demon wrote:The problem in pvc is that it fails "explosively", sending sharp pvc pieces evrywhere.


As many times as I've heard this, I've never seen it happen or heard of it happening to sched 40 or better PVC. Yes, clean-outs fly off, chamber/barrel transitions have cracked, barrels have cracked off into a hand full of pieces, 180 degree rear over and under chamber to barrel piping has cracked and/or broken loose...yes....I've seen that. However, not the thousands of glass-like shards traveling at explosive speeds ripping to shreds everything in its path....that's the image that is portrayed.

The handful of "explosive" videos I've seen were either faked or not sched 40 pipe and while I'm sure it scared the daylights out of the shooter, was far from lethal....eye injury or minor cuts and abrasions really the only possibility here...

I don't want to down play the dangerous possibility of someone abusing the material with pneumatic over pressures (pressures beyond rating) or hybrid mixes, especially over 2x...a big no-no.

Show me the evidence...

http://www.spudfiles.com/forums/barrel- ... 15893.html
The pieces of pvc flew pretty far
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Unread postAuthor: starman » Sun Mar 22, 2009 1:26 pm

I've seen that one...counts as "barrels have cracked off into a hand full of pieces".... :wink:

Scary, yes....lethal, unlikely.
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Unread postAuthor: Biopyro » Sun Mar 22, 2009 4:11 pm

ABS is absolutely fine for a combustion, and copper is great for high pressure pnematics. You have nothing to worry about.

Has anyone ever tested these supposed properties of the two plastics. I think it's a case of, it's mentioned so many times that it becomes truth, without being properly tested. This summer, I will test it on PVC, but I've never really seen ABS fittings for sale in the UK... :(

Edit:http://www.sentex.net/~mwandel/cannon/product_launcher.html

And he was using oxygen with the fuel (MPS gas?)
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Unread postAuthor: daccel » Sun Mar 22, 2009 5:16 pm

What sizes are you looking for?

Try to find an irrigation supply store. These should have a variety of sizes of pressure rated pvc. I can't imagine things are a whole lot different over in Ontario than they are here in BC.
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Unread postAuthor: Demon » Sun Mar 22, 2009 5:26 pm

When people talk of the danger of "explosive" fail of pvc and interdict it in industrial use with air, i think its when you use it to the pipe rating ( like 280 for 2 inch sch40 )

But if we use it to 1/4 of it rating, is there a danger? i mean, even if we slam it on a wall and it fail ( like my friend did to the potato launcher i sold im... ), is there enough energy to cause any body damage?


The handful of "explosive" videos I've seen were either faked or not sched 40 pipe and while I'm sure it scared the daylights out of the shooter, was far from lethal....eye injury or minor cuts and abrasions really the only possibility here...


Some people already lost there eyes cause of that and the use of gas in pvc is legaly prohibited.
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Unread postAuthor: oldchris » Sun Mar 22, 2009 6:37 pm

daccel wrote:Try to find an irrigation supply store. These should have a variety of sizes of pressure rated pvc. I can't imagine things are a whole lot different over in Ontario than they are here in BC.


OK, I'll try that. There's one nearby (vandenbush?). Don't know how they feel about less than truckload sales.

My understanding (mostly from shop compressed air world) is that the issue with PVC isn't so much holding the pressure, but impact resistance. Once the pipe gets older, or in cold temps, it becomes quite brittle. It will still hold pressure until bumped, then it lets go all at once instead of splitting like copper.
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Unread postAuthor: daccel » Sun Mar 22, 2009 6:59 pm

If you don't have any luck there.. a year or two ago I ordered some forged steel fittings from Hill Supply. Just checked and they carry pvc products including sch 80.

Not sure if they're located close to you, or whether they could cut up a length to ship. They do have nipples that you could piece together, worst case.
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Unread postAuthor: starman » Sun Mar 22, 2009 7:42 pm

Demon wrote:Some people already lost there eyes cause of that and the use of gas in pvc is legaly prohibited.


CannonCreator shot himself in the eye looking down the barrel of a loaded gun. Thankfully he recovered but after some surgery and lots of medical care. I don't know of any others on Spudfiles. There are some other vids on the net showing guys shooting themselves in the face.

Truly, there should be much more worry about shooting someone or yourself or something...just classic firearms safety.
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Unread postAuthor: D_Hall » Sun Mar 22, 2009 10:52 pm

Back to the original question (regarding alternatives).... How big of a gun are you trying to make? I'm nearing completion of a gun capable of firing a 625 fps golfball (GGDT estimate).

Materials?

Steel.
Stainless Steel.
Brass.
Aluminum.

No plastics involved. At least, not on the load-baring side of the house.

Weight? I won't lie, it's heavy. But it's still portable and will in fact be shoulder-fired. So.... Unless you're trying to make a LARGE cannon, I don't believe for an instant that such guns "must" be too heavy to be portable.
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Unread postAuthor: frankrede » Sun Mar 22, 2009 11:50 pm

Turbohacker had a reg fail and the PVC ruptured causing his dad to lose an eye.
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Unread postAuthor: starman » Mon Mar 23, 2009 2:10 am

frankrede wrote:Turbohacker had a reg fail and the PVC ruptured causing his dad to lose an eye.


Unregged CO2, yeah that will make some PVC fail for sure...bad choice of cannon materials. That's a really terrible situation with his Dad.

I did list eye injuries as a real possibility.
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