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chamber size?

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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chamber size?

Unread postAuthor: fpshutch74 » Tue Nov 06, 2007 9:04 am

im gonna make an air cannon for paintball. i was planning to make it with a two and half foot long 2in pvc chamber. but with winter coming up im starting to wonder if i should make it out of metal ( chamber only). For 1.5 in metal pipes, there are 1 foot sections( i would connect two)

my question: would a 1.5 in diameter chamber have a noticable performance difference than a 2 inch diameter chamber at the same length and pressure?

also wat is a good bursk disk for 125 psi( for a separate project)
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Unread postAuthor: gwoloshyn » Tue Nov 06, 2007 9:09 am

For your first question, I would imagine if your just shooting paintballs the chamber size would not make a noticable difference at the same psi. How close is the chamber to the valve? I could be wrong though..
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Unread postAuthor: Zen/// » Tue Nov 06, 2007 9:10 am

Never use pvc cannons when your in a cold enviorment (unless you have a deathwish), either play in the summer or build a copper/steel gun.


What kind of valve are your using?

A smaller volume chamber but with more pressure is more powerfull then a large low pressure chamber.
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Unread postAuthor: jackssmirkingrevenge » Tue Nov 06, 2007 9:26 am

How long and wide is your barrel, and what valve are you using? GGDT will give you a rough idea of the performance difference.
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Unread postAuthor: gwoloshyn » Tue Nov 06, 2007 10:54 am

Can't you use combustion cannons with schedule 40 fittings in the winter?
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Unread postAuthor: psycix » Tue Nov 06, 2007 3:57 pm

Combustions can, pnuematics not.
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Unread postAuthor: Pete Zaria » Tue Nov 06, 2007 4:38 pm

gwoloshyn wrote:Can't you use combustion cannons with schedule 40 fittings in the winter?


I sure as hell wouldn't if its very cold. PVC gets brittle when it's cold. ABS holds up better in cold temperatures, but still looses some strength.

Remember, Schedule is just a wall thickness rating and NOT a pressure rating - Lots of sch40 pipe isn't rated at all.

This page has some good info on using PVC in cold temperatures:
http://www.madisongroup.com/services/fa ... lysis.html

I keep my cannon inside for a couple of hours before I'm going to use it if it's below about 55F outside, which it is most of the winter. When I'm not using it, it gets hung from two hooks on the ceiling in my garage, which is well-insulated but not heated.

Peace,
Pete Zaria.
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Unread postAuthor: Eddbot » Tue Nov 06, 2007 10:59 pm

ok, i got two questions,
first: whenever i'm looking for pipe fittings at ace, they all say something like 'PRESSURE-1.5" COLD WATER' if PVC is made for cold water why would it get so brittle when cold
second: how cold is cold? i mean i live in the bay area of California and the past week has been above 70 when it's supposed to be the beginning of winter, but it's always like this, is it still safe to shoot if it's like 60 outside, cuz it's gonna be like that for another 3-4 weeks
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Unread postAuthor: clide » Wed Nov 07, 2007 12:46 am

Eddbot wrote:ok, i got two questions,
first: whenever i'm looking for pipe fittings at ace, they all say something like 'PRESSURE-1.5" COLD WATER' if PVC is made for cold water why would it get so brittle when cold
second: how cold is cold? i mean i live in the bay area of California and the past week has been above 70 when it's supposed to be the beginning of winter, but it's always like this, is it still safe to shoot if it's like 60 outside, cuz it's gonna be like that for another 3-4 weeks


By cold water they mean not hot. You have two types of plumbing in a house, hot water lines and cold water lines. Despite the name, cold is usually at room temperature. Also PVC doesn't typically move around and experience high shock loads in normal use so its brittleness isn't as big of a factor. In a gun brittleness can be dangerous.

Yes 60 would be fine. Personally I stop shooting when it drops below 50 degrees.
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Unread postAuthor: jimmy101 » Wed Nov 07, 2007 12:36 pm

In terms of water pipe, "cold" is generally about 50F, the temperature of the ground through which the main supply pipes run through.

If you run water out of a tap for a while the temperature will usually stabilize at about 50~55F.

NSF-pw pipe is probably OK down to a little lower temperature. In a house where the water supply lines are run through the crawl space, the pipes will cool off to less than 50F on cold days. (But hopefully they'll never get below freezing.)

NSF-pw pipe will certainly handle normal water supply pressures down to a little above freezing. Figure "normal" water supply pressure is perhaps 60 PSIG?
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Unread postAuthor: williamfeldmann » Wed Nov 07, 2007 12:47 pm

I agree with the above statements.

In general I don't shoot if it is less than 50 degrees outside, just to be safe. I don't think the pipe would have much problem until it is colder than that, but to quote Hubb the other day, "I like myself."

I also store my cannons inside on Friday nights to let them adjust to being warm if I plan on shooting on Sat. When I am not using them I leave outside in a shed. During the winter, I will store them in a closet in my woodshop since it gets bitter cold in Iowa.

Cold water out of a tap is maybe 50 degrees at the coldest. Usually more like 70, but it feels cold to you because you are 98.6 degrees (or you should be, if not contact a doctor immediatly).
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Unread postAuthor: psycix » Wed Nov 07, 2007 1:43 pm

williamfeldmann wrote:Cold water out of a tap is maybe 50 degrees at the coldest. Usually more like 70, but it feels cold to you because you are 98.6 degrees (or you should be, if not contact a doctor immediatly).


I am way above 100 F these days. :(

Got a bad cold last weekend. :(
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Unread postAuthor: fpshutch74 » Wed Nov 07, 2007 7:10 pm

alright then... say i made the chamber out of metal ...do you thing i could get away with having a plastic valve and pvc breech loading barrel set up. the barrel isnt under pressure if you dont count the force of the shot?

also if i did make a pvc chamber, do you think i could wrap the chamber with something to prevent damage to the chamber and to stop the shrapnall if it did break

someone said denim works, also im thinking mabey sliding a larger diameter pipe over that to make it look better
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Unread postAuthor: BigGrib » Wed Nov 07, 2007 7:17 pm

denim or canvas would work but if your pvc is pressure rated usually for 200 psi you shouldn't have to worry about it exploding i would use ABS for a combustion because ABS doesn't grenade like pvc does it just splits.
I dont think that there is any advantage of making a chamber out of metal. the only thing you would have is a heavier gun.
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Unread postAuthor: Eddbot » Wed Nov 07, 2007 7:46 pm

okey dokey...artichokey

don't ask...
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