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Old 09-24-2011, 12:39 PM   #1
atvan
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Default Soda Bottles

I am likely going to be a member of the Science Olympiad team from my school this year, so I was talking to my science teacher about it. One of the activities is a 2L bottle rocket. Apparently, soad bottles are rate to 320 psi, so for our use, should be more than enough.


Edit: My spelling ain't as good as my science.

Edit 2: fixed typos in the first edit reason.
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Old 09-24-2011, 01:07 PM   #2
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Default Re: Soda Bottles

2 litre bottles are fine for water rockets. Although I wouldn't trust them to anything like 320 psi. I'd say anything above 50 and you want to be somewhere safe.
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Old 09-24-2011, 01:31 PM   #3
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Default Re: Soda Bottles

Some water rockets go up to 100 psi fine, so if you are using the 1/2 rating or even 1/3 rating rule, you are good.
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Old 09-24-2011, 10:06 PM   #4
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Default Re: Soda Bottles

Sounds nice atvan. Good luck!

Many soda bottles can hold fairly high pressures for short periods of time. But the plastic will creep (slowly expand) and eventually the bottle will burst when the pressure is over a certain level. Also, pressure vessels almost always have a fairly conservative safety factor on them. Just because the bottle might burst at X psi does not mean that X - 1 psi is safe. Other loads you have not accounted for could easily take you over the limit. Generally pressure vessels have a safety factor of at least 2.5, so if a bottle bursts at X psi then X / 2.5 psi is the absolute maximum you should consider filling it to (and it's better to use lower pressures than that too).

Soda bottles are good for low pressure (~50 psi as cantab said) temporary storage of soda. Outside of that, I wouldn't trust them for much. Water rockets are fairly different than water guns and they have different safety concerns for that reason. People generally don't hold a pressurized water rocket against themselves, for example. People usually are reasonably far away from the bottle.

No soda bottles that I am aware of have a pressure rating, much less one over 100 psi. Most PVC pipe that diameter doesn't have a rating over 150 psi, and soda bottles are made of a far weaker and thinner plastic.

Soda bottles are not particularly dangerous because the shrapnel would have a low mass. But the noise could cause hearing damage and you can still get nasty cuts from the shrapnel even assuming that it doesn't go in your eyes (a worst-case scenario).

When I get the time I'm going to purge the website of any positive references to soda bottles. I can't recommend pressurizing them in water guns. Water storage at no pressure is fine.
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Old 09-24-2011, 10:26 PM   #5
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Default Re: Soda Bottles

I noticed today that the bottles have seams on them. Seems (no pun intended) kinda like a weak point to me.
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Old 09-25-2011, 03:10 AM   #6
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Default Re: Soda Bottles

They aren't reasonable for pressures that might launch a rocket, unless you just have a nose cone and some stabilizing fins.
In addittion, the only way I would consider a soda bottle is for quickfilling, and leave the pressure storage to something more robust.
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Old 09-25-2011, 09:07 PM   #7
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Default Re: Soda Bottles

Soda bottles are also built to contain mostly pressurized liquid (non-compressible) with a very small volume of highly pressurized air. Water guns and rockets tend to require far more air than that, which would create more stress simply due to the increased volume.
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Old 09-25-2011, 09:31 PM   #8
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Default Re: Soda Bottles

It doesn't change the stress. What it changes is the violence of the rupture if the bottle ruptures.
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