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Pvc strength

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Pvc strength

Unread postAuthor: fpshutch74 » Wed Apr 18, 2007 4:08 pm

i live in connecticut and the weather aint never perfrect so i was wondering about pvc strength, i know its pressure rating drops drimaticly after a 10 degree temp change in either dirrection away from 70 degrees.
also, i plan to make a breech loadable cannon for use in paintball w/ a 2 inch chamber and 1/5 inch barrel at 100 psi, i wondering if there are any stories or advice on pvc in none perfect conditions. also has anyone run into problems in the inpurities/ weak points in pvc?

by the way, i am only gonna fill the chamber right before shots and im using a reg with a remote and two pressure guages( one for the reg output and one for the chamber pressure cuz theres two valves betweem them.)
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Unread postAuthor: Pete Zaria » Wed Apr 18, 2007 4:32 pm

PVC definitely gets weaker/more brittle in colder temperatures. I wouldn't feel comfortable using sch40 nsf-pw at 100psi anything below about 50f for prolonged periods of time...

Sch80 nsf-pw will hold up better. Sleeving the chamber inside bigger pipe (maybe with a layer of insulation between.....) would help quite a bit. Leave the cannon inside (or someplace warm) til right before you're going to use it, and put it back inside when you're done using it.

ABS takes cold temperatures better, but generally isn't pressure rated - you could use ABS if you didn't want to go above, say, 65psi, though.

Or spend some bucks and make it out of metal.

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Pete Zaria.
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Re: pvc strength

Unread postAuthor: hi » Wed Apr 18, 2007 5:56 pm

fpshutch74 wrote:i live in connecticut and the weather aint never perfrect


that means that it IS perfect...

think about it, if it AIN'T NEVER pefect, then it is perfect, so whats your problem?

EDIT- ok, i wont be a smart ass, yes, draw the line at about 50 degrees. and if you do, dont go over about 40 psi. i agree with pete, use sch80 pvc or metal pipe.
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Unread postAuthor: Scope » Wed Apr 18, 2007 7:36 pm

I live in ct... the temp is pretty... well normal
what connecticut are you from??

I really wouldnt worry about it... aslong as you dont leave it outside and dont use it for like 4 hours straight.. you will be fine
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Unread postAuthor: spuzi14 » Wed Apr 18, 2007 8:14 pm

Don't you guys know it's that darn "global warming" causing these cold temps? :wink:

If the weather is constantly changing temps, like it has been in Ohio, I'd make a metal tater hater. I'm considering one this summer depending on where I work and stuff.

(tips hat to global warming)
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Unread postAuthor: AmYisroelChai » Wed Apr 18, 2007 8:50 pm

Pete you are correct metal is the safest but for paintball might be to heavy. Maybe 1" Copper would work fine for a chamber and bring the PSI slightly higher?

I like the insulated pipe in pipe idea though.
Try 1 1/2 barrel sleeved in 2" barrel fill the space with the instant foam selaer from HD - its called Great Stuff. Its sticky rapidy expanding foam.

Post a pic of your cannon when done.
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Unread postAuthor: PAspuder » Thu Apr 19, 2007 8:51 am

I ave had several guns that were made of PVC. I never liked to opperate them in cold weather, but i have shot them in temps as low as 50 degrees. I never liked to run any guns (pvc) over 80, for fear of failure. I know that sch 40 is pressure rated, but it isnt worth the risk to mea, after i had a gun blow up. That was the only time i ever had failure with pvc...I tried to put too much weight in the barrel, and when the air hit the object in the barrel, in stead of pushing it out, it blew the whole top off.

So if it helps any....I think you would be okay in COOLER weather, but not COLD. Also, if you just have to fire it....just drop your psi down a little.
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Unread postAuthor: Pete Zaria » Thu Apr 19, 2007 1:47 pm

@AMC,
I'd think copper would be fine down to at least 40F. Too much further below that it might get brittle, I really don't know.

Insulating your chamber from the cold via sleeving it inside some other pipe and filling the gap between with insulation (foam rubber, expanding foam, bubble wrap, cotton batting, whatever) would help keep the "inside" gun warm for a few minutes, but you'd still need to try to keep it warm between shots or etc....
If you do that, use NSF-PW PVC for the inside, and cell core ABS DWV for the outside layer (for two reasons, its cheap as hell and it won't shrapnel if it fails).

Another option to look into would be tracking down some pressure-rated ABS. It'd take the cold, and the pressure.

Peace,
Pete Zaria.
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Unread postAuthor: Fnord » Thu Apr 19, 2007 2:55 pm

I'd think copper would be fine down to at least 40F. Too much further below that it might get brittle, I really don't know.


From personal past experience, copper doesnt seem brittle at all in colder temperatires. Only with extreme cold is when I wouldnt use it.
Also, doesnt copper tend to fail by just making an extremely small tear? Meaning, it doesnt just explode like pvc or other metal. (when refrigerator radiators fail they usualy just from a small hole and vent from what Ive seen)
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Unread postAuthor: AmYisroelChai » Thu Apr 19, 2007 4:24 pm

just a thought you can put your 2" chamber intoa greased up 3" pipe. Fill the rest with Good Stuff (mentioned) above. Then slide out the 2" chamber now insulated with good stuff from the cold. Just a thought.
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Unread postAuthor: fpshutch74 » Fri Apr 20, 2007 9:41 am

thanks everyone, but does anyone know where i can get a 5 foot section of 2inch copper pipe.... its expencive and i only need like 5 feet
so i was thinking about asking a plummer next time we have a problem but that may be a while

also does the barrel and the chamber have to be copper, my only thought is if the burst of compressed air is two much for the pvc barrel at a cold temp, then it might fail
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Unread postAuthor: JDP12 » Fri Apr 20, 2007 11:32 am

Umm fleet farm usually should I believe fpshutch74, or maybe that's four foot sections....I forget
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Unread postAuthor: Fnord » Fri Apr 20, 2007 2:53 pm

also does the barrel and the chamber have to be copper, my only thought is if the burst of compressed air is two much for the pvc barrel at a cold temp, then it might fail


Barrels are usually a low-stress area compared to a chamber, which is why some people us abs for their pneumatic barrels. It should be fine, just dont use cell core or excede the pressure rating on the pipe.
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Unread postAuthor: CS » Fri Apr 20, 2007 4:09 pm

I have always heard it proposed that when PVC dips below 73 degrees that its strength reduces. I actually think I have proposed that from time to time as well. Although I wanted to find documentation on just how much different degrees of temperature effect the integrity of PVC, and I set out on Google to find it. Finding information on the issue was a bit of trouble as most sites documented the effects once it exceeded 73 degrees.

Anyway if I am understanding <a href="http://www.freedomplastics.com/technical/faqs.php#8">this</a> document correctly, it is proposing that PVC pipe strength increases when its temperature reduces. I am sure if you take this to any radical degree it will not hold true, but this surely contradicts the common perceptions here on SpudFiles. Although for the time being I would follow the common perception as it is sure to keep you safe regardless.

I also thought maybe this common perception proposes that PVC's impact strength drops with temperature, not its undisturbed pressure handling capabilities. As I did find documentation that states PVC impact capabilities drop severely with temperature.

PVC Pipe Failure Analysis - The Madison Group wrote:However, a very important change in property occurs as the temperature gets colder - the impact strength of PVC drastically changes for the worse. This means that at low temperatures the ability of PVC to dissipate the energy from a sudden blow is limited and may result in part failure. The best way to describe this phenomenon, apart from demonstrating the impact of several PVC pipes at different temperatures, is to graph the impact strength of PVC as a function of temperature, shown in the figure below.

<img src="http://www.madisongroup.com/services/failure/casepipe/impactpvc.jpg">

<a href="http://www.madisongroup.com/services/failure/casepipe/pipeanalysis.html">PVC Pipe Failure Analysis - The Madison Group</a>
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Unread postAuthor: clide » Fri Apr 20, 2007 4:17 pm

Yes, PVC does get stronger as the temperature decreases, but as you show it gets very brittle and that is where the danger lies. I imagine the rapid changes in pressure that the gun endures are much like an impact, and dropping the gun from even a low height could make your gun toast.
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