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PSI Max On 400 psi ball valve

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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PSI Max On 400 psi ball valve

Unread postAuthor: blindbatjosh121 » Sat Jan 12, 2008 8:29 pm

Hi i have just recently built my pneumatic interchangeable barrel potato gun with a 400 psi brass ball valve and was wondering how much psi i could crank it to safely without blowing up my pvc joints and getting hurt.
please help quickly
Josh
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Unread postAuthor: Novacastrian » Sat Jan 12, 2008 8:34 pm

Any chance of getting pics up of your launcher? I think most members would recommend not exceeding 120psi with pvc.
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Unread postAuthor: schmanman » Sat Jan 12, 2008 8:34 pm

the max pressure of the gun will be much less than 400 psi.

what diameter(s) is the pvc?

look for a pressure rating on the pipe.

the pipe is pressure rated, right?
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Unread postAuthor: LikimysCrotchus5 » Sat Jan 12, 2008 8:40 pm

Just as Nova said, probably under 150. Change the valve for better performance. A piston will be best, or you can just use a sprinkler vavle.
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Unread postAuthor: DYI » Sat Jan 12, 2008 9:26 pm

Well, theoretically, you can bring it to whatever the lowest pressure rating in the whole pressurised section is.

In practice, because of how violent and dangerous PVC failures are when the pipe is pressurised with gases as opposed to liquids (what they are designed for), you should include a safety margin of your own. I personally wouldn't use PVC pipe on a pressure vessel which held compressed gases, because it goes against manufacturers' specs, and because I want to continue living without crippling permanent injuries.

If you can get the valve to open in under 10 ms, it should be fine. If you want a method that doesn't involve massive springs / high powered pneumatic actuators, take the easy route and make a piston valve.
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Unread postAuthor: blindbatjosh121 » Sat Jan 12, 2008 9:29 pm

I know the psi i i can go up to is much less than 400. but the air chamber is 3" sch40 (everything is ) the connections are 1 1/2" and then it goes to the ball valve than back up to a 2" female adapter for interchangeable barrels. Yes its rated at like 280 psi but i don't know how much the pvc cemented joints can hold and my ball valve works fine but later when i get some more money i will change the valve to a sprinkler out but for know its fine. - whats translation? - i think i put on pictures of the gun on an attachment but not sure if it worked- sorry if it doesn't make sense i was in a hurry
Josh - plz help
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Unread postAuthor: DYI » Sat Jan 12, 2008 9:37 pm

PVC cemented joints are the strongest part, as they solidify into a single piece, unlike threaded fittings.

As long as everything is pressure rated, PW, SCH 40, you should be able to use it at 100 psi without being in loads of danger. For future projects however, try to avoid using materials that shatter and produce high speed shrapnel when they fail.
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Unread postAuthor: blindbatjosh121 » Sat Jan 12, 2008 9:54 pm

What materials should i use because in my area ABS is hard to find. Copper?
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Unread postAuthor: DYI » Sat Jan 12, 2008 10:09 pm

Copper is a good choice. While it is rather expensive in comparison to PVC, it is rated for use with compressed gases, and has a much less lethal failure mode.

I would suggest steel though, for everything but the barrel. It is available, cheap, and has very high pressure ratings, as well as not having the sensitivity problems that some plastics have. If you live in the States, you can get threaded steel/iron pipe and fittings in up to 6" sizes from McMaster, but the fact that you don't have truck sized wads of money lying around means that 4" is the general limit.

Loads of people build PVC pneumatics without blowing themselves up, it's just that I like to take the safe approach as opposed to the cheap one.
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Unread postAuthor: Maniac » Sat Jan 12, 2008 10:11 pm

not abs it is not good at really any pressure. its not that its unsafe but that it rips down the side of the pipe above 50psi to my knowledge. And yes copper is what most people go with because its readily available and strong and safe and metal and can hold high pressures and i cant think of anything else.
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Unread postAuthor: blindbatjosh121 » Sat Jan 12, 2008 10:13 pm

ya i like the safe aproach menards or ace got all this stuff to in my area
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Unread postAuthor: DYI » Sat Jan 12, 2008 10:21 pm

Maniac, it is usually a good idea to not make generalisations, and to know at least the basic facts before offering advice.

Pressure rated ABS is safe to use at whatever pressure it's rated for. DWV ABS has been pressure tested to 120 psig for several hours, although due to lack of quality control it is not advisable to use DWV ABS in continually pressurised systems.

ABS is a more useful material in barrels however, or in oxygen enriched combustion guns. I've used a 3" DWV ABS barrel on my 500 psi burst disk gun with a projectile that weighed 2.5 pounds and literally had to be hammered into the breach, at 25 degrees fahrenheit. The barrel remained completely unharmed. The fact that it has the best failure mode possible, and that it can literally survive more than twice its burst pressure in a rapid shock makes it a very useful material. Copper barrels are rather better, but a 12' x 3" copper tube would be mind-bogglingly expensive.

@blind...: If there's anything you can't find at a local hardware store, just get it from McMaster-Carr. They ship to individuals, deliver in less than 48 hours to anywhere in the lower 48 states, and have everything. Absolutely everything.
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Unread postAuthor: SpudBlaster15 » Sat Jan 12, 2008 10:30 pm

DYI wrote:I personally wouldn't use PVC pipe on a pressure vessel which held compressed gases, because it goes against manufacturers' specs


So using 150PSIG rated malleable iron pipe and fittings at 450PSIG is withing the manufacturer's specifications?:lol:

In all honesty, (assuming the solvent welds are created effectively) you should be safe to use the launcher at any pressure <200PSIG>150PSIG to rupture without success.

Even though the pipe is not rated for use with compressed gases, it is rated to sustain extended periods of internal pressurization of up to 280PSIG, with a safety factor of 3 employed.

PVC pipe failures really aren't as hazardous as most believe them to be. Sure they are spectacular, but the lightweight shrapnel is highly ineffective at penetrating flesh. A 6" long, 1.5" nominal diameter Sch 40 PVC pipe was filled with black powder and placed next to a block of gelatin inside a plywood box. The force of the explosion blew apart the box and the gelatin block, but even with a maximum theoretical internal pressure of ~1500PSIG, even the larger fragments managed to penetrate less than 1/8" into the surface of the gel. An airsoft BB fired at ~600fps will achieve more penetration into the gel.

Hearing and eye protection should be sufficient to prevent any potential injuries caused by PVC shrapnel.

ABS, steel, and copper are safer materials, but ABS is difficult to find for many individuals, copper is very heavy and usually expensive, and steel is also very heavy, and difficult to find in nominal diameters larger than 2".

If you can find ABS, use it. The raw material's tensile and yield strengths are very similar to that of PVC, which means pipes with identical dimensions should have very similar burst pressures. In addition, ABS has a much higher impact strength, and maintains its resilience at temperatures down to ~-25*C, which in layman's terms means that it will not become brittle (and thus lose it's high impact strength) until said temperatures are reached.
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Unread postAuthor: DYI » Sun Jan 13, 2008 11:59 am

So using 150PSIG rated malleable iron pipe and fittings at 450PSIG is withing the manufacturer's specifications?


:D Point taken, but they don't fail quite as spectacularly as PVC, and they have been tested up to more than twice the pressure I use them at, so I feel reasonably safe. And you quoted a burst pressure of over 2kpsi for the 2" welded steel pipe.

PVC shrapnel won't always do damage, but Turbo's dad lost an eye to it, and one person almost had their jugular vein sliced by it. So, like smoking, while it isn't always fatal, it should be avoided if possible. And seamless copper tubing (the only kind) can hold higher pressure per weight than SCH 40 welded steel pipe (the most common kind).
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