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It would help but I still wouldn't risk it. If you can find pressure rated ABS, go for that.
If it's PVC, it's brittle in the cold. IMO, this is a bad idea all together. Ask yourself: Whats behind a snow fort?
When life gives you lemons...throw them back they suck!
BTW, when I recommended ABS, I did so because it can handle the cold far better then PVC, and if it happened to fail, it will simply tear apart. No shrpanel.
It's just not a good idea, and it won't really work. If anything, make a surgical tubing slingshot and use that to fling snowballs.
from experience I have used 3/4 sch80 in the snow and it works ok but not great I wouldn't trust it. It is still really brittle. to day I built me a 2inx24in copper barrel. and I shoved the hole thing with snow and really compacted it. I shot it at 100psi. I have to say snow is one of my favorite things to shoot. It it had some kick to it I love it. Ill post a video in the next couple days.
here is a question, What temperature does PVC become brittle enough? How long does it take for PVC to be out in the cold before it reaches that temperature?
Reason I ask is because I have messed around with PVC enough to know that it really doesn't feel that cold or hot, so does it change temperature quickly?
Does PVC have a high enough conduction to quickly become brittle?
I know if you have a piece of metal outside in the cold for 5 minutes it will be extremely cold on the touch, but when you have PVC outside in the cold it really doesnt feel cold at all...
Do you think it really is just over-cautious of us to treat PVC/cold weather?
I will admit that before I joined this site, I have built a few cannons and used them in -25c (-13F) loading them up with snow and ice chunks and fire them for hours. I never noticed the PVC getting that cold to the touch.
Now I know if you have direct coldness directed to the cannon at one spot for too long it can become brittle(co2 inflator directly to the side of a pvc piece). But does the temperature of the outside air really effect the PVC so much that it can reach that critical brittle temperature?
PVC will settle to the temperature of the surrounding air just like anything else. However, just because something doesn't feel cold doesn't mean it isn't cold...it just isn't good at conducting heat out of your skin very quickly.
You feel the same effect walking from your carpet floors to the tile floor in the bathroom. The carpet and the tile are exactly the same temperature but the tile is much quicker at drawing heat from your feet than the carpet is. PVC is the carpet.
fair enough, how long will it take to settle to the tempature of the surround air and how cold is cold enough?
Challenging Question time:
If a person with a 2" Sch 40 PVC pipe is held in a house at 70 Degrees F, and It is put outside in 15 Degrees F weather, How long will it take for the PVC to reach around 15 Degrees F? Also How long would it take for it to get to a temperature that is dangerously brittle?
Last edited by Davidvaini on Tue Feb 10, 2009 11:56 pm, edited 3 times in total.
Another note is that while firing a combustion it does heat up the chamber so the chamber will be fine after a few shots but the barrel becomes very cold. Sgort once said he cracked a blue flame just above freezing outside.
According to this page...
PVC pipe is pressure rated at 73° F (23° C). As the temperature drops below 73° F the pressure capacity increases and is usually considered an additional safety factor and not taken into account. However, as the temperature increases above 73° F, the pressure capacity of PVC pipe decreases and the pressure capacity must be de-rated.
Other official things I've read say you should derate pvc 50% below freezing...so who knows...
Another theory on "brittleness" at cold temps could be just simple thermo-mechanical expansion/compression of the material, not necessarily brittleness. However, I am just theorizing here, I don't know for sure and info on the subject is a little scarce.
hmm.. until I get some sort of proof all I can go off of is what I have seen and experienced. Otherwise its just safety conscious hype.
I have personally used a 2 inch sprinkler valve cannon in Wisconsin winter temps of -15F for multiple hours in a row shooting snow balls and nothing happened. I have done it multiple times.
I know what you are gonna say, "Its could be just luck that nothing happened and its better to be safe then sorry"
Point I'm trying to make is until we get some solid facts or figures on this, we should try not to exaggerate coldness issues. I think it would be pretty pathetic if this got carried away like the DWV situation a while back. (When people said DWV could only hold 10psi.)
Now obviously DWV isnt pressure rated and cannot hold as high of pressures as NSF-PW pipe, and obviously pvc does get brittle with cold temperatures, so it is better to be safe then sorry, but lets not get carried away.
I think what was said back then was that DWV isn't even rated to hold 10psi. Just reinforicing the fact that it isn't rated for use with pressure.
PVC is brittle at all temperatures. . . it's a question of how hard you have to hit it before it shatters.
Proof? I've shattered multiple pieces of 1.5" SCH40 while using it as carpet beaters on a summer afternoon. Of course, I was a mite annoyed to be beating carpet in the first place, so I was working off some steam, wasn't watching what I was doing, and hit the tree branch holding the carpet, (yeah, and it took me four times to learn the lesson. . .) But, anyway. . .
The point I was orignally going to make is: soda bottles used to be glass. Beer bottles still are, in most cases, as are champagne bottles. Therefore, obviously brittleness alone doesn't preclude using a material as a pressure vessel. . . we just have to respect the limits of the material.
In this case, respect equates to: don't drop a pressurized chamber, and don't pressurize a chamber that has been dropped until you can hydrotest it. This goes double in the winter. The good news: snow tends to be a good cushion against impact damage.
(Hydrotest made easy: fill chamber to be tested as full as you can with water, then pressurize using a pump until you see 150% of normal pressure on the gauge. (you DID put a gauge on your cannon/pressure source, right?) Wait several minutes (I like 30) and check the gauge for a pressure drop. I personally condemn a chamber for any pressure drop that is not obviously a bad valve or fitting.)
it's best to do your hydro work in a garage or other place with reasonably stable temperatures and shade.
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