Comment by amluto
13 hours ago
That’s a crappy pressure vessel holding 350ml of 80psi air, for about 100J of stored energy. I’m not entirely sure I’d be comfortable with that, especially anywhere with my face in the line of fire it it fails.
13 hours ago
That’s a crappy pressure vessel holding 350ml of 80psi air, for about 100J of stored energy. I’m not entirely sure I’d be comfortable with that, especially anywhere with my face in the line of fire it it fails.
Your bike already has two crappy 80psi pressure vessels, why not three?
Those two pressure vessels are highly engineered and are wrapped with materials with pretty good tensile strength. Also, they’re made out of materials (fabric and rubber) that absorb a decent amount of energy when they tear and that don’t fragment. And the whole assembly usually depressurizes slowly.
Having personally blown up beverage bottles by overpressurizing them (be very very careful doing this!), when they go, they go violently.
I've blown up beverage bottles for fun. Hooking an air compressor to a 2L bottle and exploding it makes a satisfyingly loud boom.
*We had a valve on the air line so we could be at a safe distance when pressurizing. Be very careful. It's unpredictable exactly at which point they'll blow. Sometimes they hold full pressure for a couple seconds and then go.*
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If this is a modern bike, 80psi is way too high. 50psi is sufficient and will give you a more comfortable ride as well as higher efficiency on real-world surfaces.
80+psi is for old-style road bikes with narrow 23mm tires. Modern bikes (even road bikes for racing) don't use these any more; 28mm is the minimum these days.
Not to be pendantic (but to be pendantic) 80psi is the correct pressure for 28mm tires ridden briskly on good roads. At least according to ye olde Silca tire pressure calculator. Back in the day when folks ran 23mm tires they would typically run above 100psi (though that may not have been optimal...).
… I have a modern bike (a Specialized). The tires' rated range is 75psi to 100psi. I usually pump it to around 80–85psi. The tires are 33mm.
It's a soda bottle - it fits in your water bottle holder, and you can replace it for a couple of bucks if it fails. 80 psi is pretty low pressure (typical narrow tires are 100-120) and the bottle itself is very low mass, so the fabric around the bottle should ensure safety if it bursts.
IIRC these came out in the early-mid 90s; a bike messenger trick at the time was to fasten the horn to your handlebars with velcro, so you could take it off and hold it near a car window when triggering it.
I suppose I should maybe not worry about 80 psi so much. An ordinary bottle of soda on a moderately warm day is around 80psi. The energy is 1/2 * pressure * head space (roughly), and head space is minimal. But you can chill it in the fridge, then open it and quickly pour out half, then close it and let it warm up, and you may still be near 80 psi, and I’ve never heard of anyone getting maimed by an exploding soda bottle.
If it fails by blowing the end off toward your face what damage will it do?
> That’s a crappy pressure vessel
That's a huge assumption, and likely incorrect.
Good point, but I abused it pretty well and it seemed to do OK - was also in a water bottle holder so closer to the legs than anything.