I have been filling my 2 liter soda bottle air reservoir (for my Air Zound) to 120 PSI.

Anyone have a guess to how high the pressure is to failure?

https://galileo.phys.virginia.edu/out...Newton3Frm.htm

"Note: The industrial specifications for the pop bottles maintain that the bottles can withstand 180 psi. For maximum safety, do not exceed 90 psi."


This was in reference to 2 liter bottles...not sure how reliable the info is. I would have to assume that sun exposure and general aging would diminish the max over time. Remember that the PSI will increase with temp.

Where did you get the two liter bottle? Just used a normal soda bottle? Is there any advantage to using the larger bottle? Extra loud sound, perhaps?

I'd think just more blasts with volume, louder sound would be a result of pressure.

I use the OE bottle, at the recommended pressure of 80psi, this provides plenty of loud blast for my riding. That and I top off when I check/fill my tires.

Stacey is correct.

More pressure = higher velocity air flow = louder sound

More volume = will maintain pressure longer = more horn blasts.

I had never heard of this Air Zound (but I just looked it up)! I've been using dingdong bells. Now I gotta get one! I'll hook it up to my scuba tank.

I'm so glad I fired up BF for my break time reading!

But to the original question...

The maximum pressure a cylindrical vessel can hold is given by:

stress = (pressure * diameter)/2* (wall thickness)

Looks pretty simple. These bottles are made of PET, so let's just assume a tensile strength 7,977 psi. Diameter is about 4.3 inches. Wall thickness is about .017 inches. (I'm pulling numbers out of the air here).

Solving for burst pressure:

(7,977psi)*2*.017 inches/4.3 inches = 63 psig.

You get the idea...

The problem is that under a constant load, plastics tend to increase in length or "creep". Different polymers vary in how much they creep. Teflon is one of the worst! Eventually, the bottle will burst just because it keeps growing. Wall thickness reduces and OD increases. A recipie for disaster in the pressure vessel business!

Does it change things when the container is wrapped? The OEM bottle is wrapped with a plastic cloth that works well with velcro.

What we need is an equation that tells us how much louder the horn will be for all that higher pressure. I suspect that the small plastic horn limits the maximum decibels no matter the pressure.

Unless you're using the horn to cheer on a football game, the horn out of the box is already pretty loud and long.

Should test a bunch to destruction and find out

As for the wrapping, I doubt it would do much. The shear strength of the velcro wouldn't make a difference. It will keep all the exploded pieces together, though

But you gave me an idea...my sons' air bottle for their paintball markers are fiberglass wrapped. That little cylinder is strong, and can handle a high pressure.

As for decibels as a function of airflow or pressure, that's a very complicated subject. That simple hoop stress equation I posted earlier probably put half the forum to sleep. We don't even want to get into airborne noise equations.

You are probably correct in presuming it has a decibel limit...based on size and materials.

I still want to know where the OP acquired a 2L air-zound!

The AirZound is great for when you just gotta get someones attention. Like the MUP and a jogger has an IPOD. You should see them crap their pants!

Empty Mt. Dew bottle.

I carry one of these attached to my floatation device while diving or boating. I carry it while backpacking too. It's hurt-your-ears loud even with my limited wind power (some may dispute this).

I can hardly wait to get ahold of an air zound!

BTW, one of the best places to buy it is on Amazon.com -- right now going for $18 and free shipping if you buy enough qualifying stuff (like books, maybe).

I've seen that whistle and looked at others. What I want is a whistle or horn that is pitched low. Shrill sounds may get attention, but low-pitch commands more respect on the roadway. Maybe this isn't possible with light-weight components.

The other problem with whistles is how to get them from your lanyard into your mouth when you need them. When you most need them you're probably already in fast-moving traffic and don't want to make that motion. You can carry it in your mouth as you go through intersections ... if you don't mind drooling all over.

What ? WHAT? WHAT?

https://www.bikeforums.net/commuting/340524-air-zound-exploded.html

That's exactly what it's for, they eventually blow up. The pieces are so light anything will stop them.

I got one awhile back for my wife. Two things to keep in mind:

They come with air in them, so don't squeeze the trigger to see how it works while it's anywhere near your face;

They can wake the dead.