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2 Liter bottle burst pressure

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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2 Liter bottle burst pressure

Unread postAuthor: skyjive » Sat Dec 25, 2010 1:31 am

So as a sort of fringe benefit of having spudding stuff laying around, I realized I can carbonate my own beverages with my CO2 bottle. My family goes through about 20L of seltzer a week so it might actually have practical value (!). Anyway, here is my setup: CO2 bottle to QC to modified bottle cap with homemade stainless/neoprene bulkhead fitting. Fill bottle to curvy part at top, hook up CO2 at 75 psi, shake for 10 sec. Instant seltzer!

Image

The question part of this post is: what is a typical burst pressure for these bottles? I feel a little wary loading up a thin, large-diameter plastic vessel to 75 PSI and shaking it when full of water. Not mention, what will the failure mode look like?

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Unread postAuthor: Crna Legija » Sat Dec 25, 2010 6:59 am

iv had coke bottels up to 120, never burst one tho
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Unread postAuthor: SpudFarm » Sat Dec 25, 2010 8:36 am

I feel a little wary loading up a thin, large-diameter plastic vessel to 75 PSI and shaking it when full of water. Not mention, what will the failure mode look like?


Full of water?
Hydrostatic testing is pressure testing with fluids to prevent energy building up in the vessle before it burst.
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Unread postAuthor: saefroch » Sat Dec 25, 2010 11:10 am

Failures normally occur at 140-160psi. 75 is perfectly fine, as most 2L bottle rockets are launched at 120psi and I've never seen one fail at that pressure. They only fail when they're stuck on the launcher and over-pressurize. Failure mode? Localized shear where the layers inside the plastic aren't bonded as strongly as the rest, then a rippled tear along the height of the bottle. Some shrapnel, but a scary as it sounds, it's not hazardous to be 10 feet away when it fails, unless you have terrible luck. The air resistance of the bits of plastic is so huge you'd have to be holding the thing when it goes boom to be injured. If it's mostly full of water, I wouldn't be concerned at 75 psi. Just make sure there aren't any stress marks or other damage to the bottle.
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Unread postAuthor: metalmeltr » Sat Dec 25, 2010 1:28 pm

I have had them blow up in my hands, stings a little and is really loud but no a real harm.
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Unread postAuthor: omniscient » Sat Dec 25, 2010 3:59 pm

The reason why the PET plastic bottles finally rupture is a combination of heat and pressure. A PET plastic bottle will easily explode @ 75-100psi, so long as the bottle is dry (inside and out) and the surrounding temperature is above 50 degrees (F).

Adding a small amount of liquid to the inside of the bottle, seems to help dissipate the heat of the compressed air... CO2 is colder than compressed air and with addition of filling the bottle up to the curve with a liquid, is why your bottle(s) have not yet failed at 70psi.

When a PET plastic bottle does rupture, the blast is violent... more than sufficient to turn your hand into hamburger meat. The cap can explode, causing serious injury, as well as the liquid contents. If the point of rupture were on your hand, I'm sure it would easily inject the CO2 gas and the liquid under your skin, as well... Please, also consider the risk of being permanently blinded, by either plastic shards from the cap, or from the liquid streaming into your eyes.

Anyone here who would tell you that what you've described is safe to do, doesn't know their ass, from a hole in the ground. (to put it as mildly as possible).
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Unread postAuthor: Lockednloaded » Sat Dec 25, 2010 4:48 pm

omniscient wrote:When a PET plastic bottle does rupture, the blast is violent... more than sufficient to turn your hand into hamburger meat. The cap can explode, causing serious injury, as well as the liquid contents. If the point of rupture were on your hand, I'm sure it would easily inject the CO2 gas and the liquid under your skin, as well... Please, also consider the risk of being permanently blinded, by either plastic shards from the cap, or from the liquid streaming into your eyes.

Anyone here who would tell you that what you've described is safe to do, doesn't know their ass, from a hole in the ground. (to put it as mildly as possible).


from an actual "hands on" experience with this:

metalmeltr wrote:I have had them blow up in my hands, stings a little and is really loud but no a real harm.
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Unread postAuthor: velocity3x » Sat Dec 25, 2010 4:56 pm

Lockednloaded wrote:from an actual "hands on" experience with this:

metalmeltr wrote:I have had them blow up in my hands, stings a little and is really loud but no a real harm.


You'd be wagering your hands that nothing will go wrong. That's a pretty high and senseless price to pay if you loose.
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Unread postAuthor: Biopyro » Sat Dec 25, 2010 5:28 pm

I've found them to start swelling around 110 (yield strength i think) and then swell a bit and go about 120psi. As above with the safety precautions. Yes they could be harmless, but it's not hard to put a safety screen up.

On the plus side, water is not compressible so having them full with water will reduce the contained energy.

Keeping them cool will increase the amount that will stay dissolved, and shaking them more will cause faster dissolution, but definitely don't use your hands.
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Unread postAuthor: metalmeltr » Sat Dec 25, 2010 5:31 pm

On a side note this must be how soda stream works.
Buy the flavoring and your money ahead.
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Unread postAuthor: D_Hall » Sat Dec 25, 2010 6:08 pm

One thought...

Does CO2 come in different grades like O2 does?

More to the point: O2 comes in different grades. Industrial grade O2 will have trace amounts of other stuff in it. Blah blah blah. Suffice to say that you shouldn't be breathing it. If you want to breath it, you need to purchase medical grade O2.

Could I make a similar statement about CO2? Could somebody with more knowledge say something like, "Industrial grade CO2 will have trace amounts of other stuff in it. Blah blah blah. Suffice to say that you shouldn't be drinking it. If you want to use it for seltzer (ie, drink it), you need to purchase food grade CO2."

Honestly, I have no idea.... Anybody?
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Unread postAuthor: metalmeltr » Sat Dec 25, 2010 6:12 pm

I have been told the only diference between medical and industrial O2 is the valve on the tank
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Unread postAuthor: D_Hall » Sat Dec 25, 2010 6:17 pm

metalmeltr wrote:I have been told the only diference between medical and industrial O2 is the valve on the tank

The valves are different, certainly. I've also heard tales about allowed particulates in the tanks and such. IE, the *gas* may be the same, but that doesn't mean that the *system* is the same. I've heard so many conflicting versions that honestly I'm not sure what or who to believe. But one thing I know: It's not worth it to find out that I'm wrong so unless I find myself in a real-life action movie, I'll stick to medical grade.
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Unread postAuthor: Biopyro » Sat Dec 25, 2010 6:24 pm

O2 is a slightly different beast.
You're inhaling it. The stomach is designed to deal with all sorts of nasties. It will vet them, and usually manage to eject what's not good.
The lungs aren't quite as capable and will much more readily absorb or deposit what gets in.

Oxygen for medical purposes is designed to be safe for round the clock use for long periods of time. As I mentioned before, the lungs aren't great at ejecting what gets in, and so if there's just a few impurities, they can accumulate.
I'm sure I needn't mention that the gut is very good at expelling what gets in ;).

Of course, the impurities may be unimportant, but if you're running a medical supply company and someone will be breathing your product every day for 24 hours for the foreseeable future, the last thing you want is to be implicated in their death.
TL;DR

Oxygen is used for a long time in the lungs. Things accumulate or are absorbed and can be dangerous.
CO2 in drinks is used for a short amount of time. Gases are burped out and solids are excreted. It shouldn't be dangerous.
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Unread postAuthor: Moonbogg » Sat Dec 25, 2010 6:31 pm

Its a good point about the safety in consuming that stuff coming out of a non food grade cylinder. About the danger of being hurt by the bottle busting, i'd say the chance for injury is there so where safety glasses at least.
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