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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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Unread postAuthor: saefroch » Sat Dec 25, 2010 6:47 pm

omniscient wrote: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).
Please no insults here. I have significant personal experience with launching bottle rockets at 120psi. (And with three exploding at ~160psi about 5 feet from me, no shielding, no injuries) None have ruptured unless the pressure is allowed to go past 120psi. The failure from a 2L bottle mostly full with water will not be very violent, since there is little compressed volume to expand. Precautions are always recommended, in case you are pressurizing a flawed bottle, and get incredibly unlucky.

I doubt the normal CO2 one purchases will have enough impurities in is to cause any problems... after all, it's not like you inhale all the gas out of the top of the bottle, you drink the water and whatever compounds have been formed in the reactions between the pressurized gas and the water, with concentrations according to their K value. I don't think any gas will be present in sufficient concentration (and thus a significant partial pressure) to produce a measurable amount of product. Although... there is such a thing as "beverage grade CO2," so I'd be wary of the stuff before drinking it.
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Unread postAuthor: Insomniac » Sat Dec 25, 2010 9:03 pm

As far as I know, what you're doing is relatively safe.

A pressurized bottle with little to no liquid in it is dangerous at close range. They explode with a hell of a bang (hearing damage is likely), the plastic gets quite torn up and mangled (I can't be sure, but I can almost guarantee that there is significant possibility for injury if you were holding it at the time), and the shrapnel, albeit very lightweight and not very numerous, warrants the use of safety glasses if you're close to it. It doesn't take long to put on some glasses, but the possible consequences for not doing it, although unlikely, are lifelong.

However, if you're filling it completely with water first, the story changes a lot. I still wouldn't advise holding it, as it's unneccesary and things can still go wrong, but the amount of stored energy is minimal. I'd still whack on some safety glasses, say in case the cap failed, but other than that I can't see a failure being particularly violent. Regular bottles of soda are at a fair pressure in the supermarket, and we don't hear about many injuries caused by those.

I think you'll find this helpful.
[youtube]http://www.youtube.com/watch?v=a_QvUC3EqxA[/youtube]
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Unread postAuthor: omniscient » Sat Dec 25, 2010 10:59 pm

saefroch wrote:
omniscient wrote: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).

Please no insults here. I have significant personal experience with launching bottle rockets at 120psi. (And with three exploding at ~160psi about 5 feet from me, no shielding, no injuries) None have ruptured unless the pressure is allowed to go past 120psi.


If you remember the author's original post:

skyjive wrote:. Fill bottle to curvy part at top, hook up CO2 at 75 psi, shake for 10 sec. Instant seltzer!...


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?


Launching a 120psi-charged 2 liter bottle rocket from 5 feet away and holding one at 75psi, are 2 completely different things.

Where we differ, is that I have had considerable experience in purposely causing 2 liter bottles to fail. Have you ever noticed how much harder the plastic is, after the bottle fails? The plastic is heated, stretched and then immediately cools... in a sense, "tempering" the plastic (for lack of a more intelligent description).

The caps can fracture, the installed fitting(s) can fly out and smack you in the mouth and knock half your teeth out... can embed themselves in your eyeball and blind you, or tear the skin, muscle and tendons on your fingers apart.

Holding ... I repeat; holding a pressurized PET plastic bottle is not a safe practice.
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Unread postAuthor: metalmeltr » Sat Dec 25, 2010 11:06 pm

If you are truly that paranoid get a full face shield.
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Unread postAuthor: omniscient » Sat Dec 25, 2010 11:37 pm

metalmeltr wrote:If you are truly that paranoid get a full face shield.


Oh... didn't think of that!... and it would protect my hand, as well! :roll:

Please excuse me out of this discussion, for the time being; I'm going to straddle my golf-ball hybrid and ignite a 2x acetylene mix. - I don't have a full-face shield, but figure that <a href="http://shop.naturesgrub.co.uk/WebRoot/Store3/Shops/es114020_shop/4B82/BED9/BD63/DCBB/B065/0A0F/1117/CADD/2.5ltr.jpg" target="_blank">this</a> will do?
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Unread postAuthor: Insomniac » Sun Dec 26, 2010 12:37 am

No, just wear safety goggles and hopefully you'll be fine. Then again, I've heard that the goggles do nothing.

Anyway, provided there is as little gas in the bottle as possible, and gloves are worn to help prevent any cuts which could occur with a failure, I'd say it's relatively safe. Soda bottles are pressurized when you buy them, yet you don't treat them as though they were filled with nitroglycerin...
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Unread postAuthor: saefroch » Sun Dec 26, 2010 12:52 am

omniscient wrote:Holding ... I repeat; holding a pressurized PET plastic bottle is not a safe practice.
But thousands do every day :wink:.

omniscient wrote:Launching a 120psi-charged 2 liter bottle rocket from 5 feet away and holding one at 75psi, are 2 completely different things.
Very much agreed. The first has a high chance of rupturing but probably won't injure you if it does, and the second has a pretty low chance of rupturing, and will almost certainly cause small injuries (but certainly not fatal) if it does.

omniscient wrote:The caps can fracture, the installed fitting(s) can fly out and smack you in the mouth and knock half your teeth out... can embed themselves in your eyeball and blind you, or tear the skin, muscle and tendons on your fingers apart.
I guess you have considerable personal experience in this too?

omniscient wrote:Please excuse me out of this discussion, for the time being; I'm going to straddle my golf-ball hybrid and ignite a 2x acetylene mix.
If it's made out of sch 40 steel like it should be, that would be far more awkward than dangerous.

What I'd reccomend if one is going to do this is to fill the bottle completely with water, then pressurize it to 75 psi with CO2, and use a magnetic stirrer to mix the solution. However, this site suggests that you wouldn't need to set your regulator any higher then 55 psi to carbonate water.

EDIT: Does anyone know how to calculate what pressure of CO2 would be required to produce a solution with a pH of 2.5? I don't know how there can be both a concentration and a pressure in a Ksp expression...
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Unread postAuthor: Biopyro » Sun Dec 26, 2010 5:33 am

http://en.wikipedia.org/wiki/Carbonic_a ... _solutions
This only goes to 10 bar, but I suspect you'll struggle to get such a low pH with such a weak acid.
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Unread postAuthor: Technician1002 » Sun Dec 26, 2010 9:47 am

Just a note on industrial grade O2. Most of the time is is the same stuff, but the medical is tested and certified to have safe levels of CO in it. Too much carbon monoxide is OK for welding but not for breathing.
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Unread postAuthor: saefroch » Sun Dec 26, 2010 1:33 pm

Biopyro wrote:you'll struggle to get such a low pH with such a weak acid.
I saw that table, but there's also this, although it is possible that those lower pH values are due to the Vitamin C and citric acid:
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Unread postAuthor: skyjive » Sun Dec 26, 2010 9:23 pm

So it looks like this might be a case of "it's probably safe, but...". There seems to be some ambiguity about whether

1) The chance of having a bottle burst is acceptable small
2) OR the consequences of such a burst are acceptably mild
3) AND the chance of dangerous impurities in the drink is acceptably small

I think that paying the 99 cents for industrially made seltzer, while highway robbery given cost of manufacture, is not too much for knowing its safe. Oh well, back to the supermarket.

EDIT

I just remembered that my CO2 supplier is a homebrew beer shop, so I think I actually CAN assume this is safe for human consumption.

So I'll just build like a wooden box or something for burst containment and it should be safe. I assume no one disputes that a wooden box would contain the rupture event?
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Unread postAuthor: metalmeltr » Sun Dec 26, 2010 10:31 pm

A wooden box could easily contain the rupture.
As far as agitation is concerned this could work.
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Unread postAuthor: saefroch » Sun Dec 26, 2010 10:56 pm

A wooden box will contain the rupture, but even so I recommend filling the bottle up to the neck with water before pressurizing with CO2. If you're agitating the bottle sufficiently, it shouldn't matter if there is only a small interface.

If you've agitated the bottle and possibly banged it around inside the box and it hasn't ruptured, I'd be fine holding it, especially given that it's only at 75psi, and my first ball valve cannon had a 2L soda bottle repeatedly taken up to 120psi.

When you complete this device, it would be interesting if you could test the pH of your seltzer and compare it to store brands.
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Unread postAuthor: cavemanaston » Mon Jan 03, 2011 3:36 pm

ok i did my own testing as i initialy used 2 2litre bottles for my first cannon
i tested them totally full of air and they always seemed to burst at 125 psi
and if the same bottle is contiuiusly used it cans trech and weaken so i recomend replacing the bottles every so often


and i have had a bottle blow up against my leg at aprox 90 psi and after the scriest moments of my life i realised i was fine.

to add some protection you could wrap the bottles in a strechy type of sticky tape so that the bottle can break and air leak out without and shrapnel being shot anywhere

hope this helps
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Unread postAuthor: FighterAce » Mon Jan 03, 2011 6:19 pm

I once went crazy and spent a roll (5 meters) of military grade duct tape on a coke bottle... I used my setup to attach it to a shock pump and pumped away.
It reached 30 bar with no problem. After that I just vented all the air and never repeated the test because it was pretty scary.

It was done behind almost closed doors :D me and pump on one side and the bottle on the other.

I really don't recommend trying this.
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