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Max air pressure in an innertube?

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Max air pressure in an innertube?

Old 10-01-21, 09:19 PM
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Max air pressure in an innertube?

Anyone have a pressure gauge accurate enough to measure the maximum pressure in an inner tube before it explodes? With the tube NOT in a tire. Any guesses on what that pressure might be? IMO, any bicycle or automotive air pressure gauge won't even register at such pressures.
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Old 10-01-21, 09:23 PM
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Why would someone do that?
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Old 10-01-21, 09:24 PM
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Old 10-01-21, 09:43 PM
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Not much. Not sure why anyone would ever want to know this and what they'd do w/ the info.
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Old 10-01-21, 09:59 PM
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Originally Posted by rickpaulos View Post
Anyone have a pressure gauge accurate enough to measure the maximum pressure in an inner tube before it explodes? With the tube NOT in a tire. Any guesses on what that pressure might be? IMO, any bicycle or automotive air pressure gauge won't even register at such pressures.
I don't think it would be that high. Tubes get pretty big before they pop, much bigger than the tires they fit in, and with increased volume, you get lower psi. I'd guess PSI goes up for a few strokes, then kinda plateaus, maybe only increasing fractions of a PSI every stroke til POP!

Last edited by LesterOfPuppets; 10-01-21 at 10:04 PM.
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Old 10-01-21, 10:14 PM
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This one might work, just rig it up inline in your pump hose.

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Old 10-01-21, 10:20 PM
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Originally Posted by rickpaulos View Post
Anyone have a pressure gauge accurate enough to measure the maximum pressure in an inner tube before it explodes? With the tube NOT in a tire. Any guesses on what that pressure might be? IMO, any bicycle or automotive air pressure gauge won't even register at such pressures.
Inner tubes are basically just rubber balloons, they can barely contain any pressure at all. When you add air to them, they mostly just grow bigger, rather than seeing substantial increases in pressure. They pop when they stretch out so much that the material tears, much like party balloons.
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Old 10-02-21, 04:41 AM
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Old 10-02-21, 07:50 AM
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Back of the envelope calculations for butyl rubber suggests to me that you should get to 10's of psi with a 1" tube. It will be lower than "theory" because there will be a relatively thinner portion that will bulge and will be the failure point.

I suspect you could see it with a normal pump gauge on a small diameter tube.

I'll put my marker at 10 psig.

Yes on doing it safely. Maybe have it on the other side of a door so you are protected. Make sure the dog's with you...
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Old 10-02-21, 08:37 AM
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When you put the tube inside a tire then it becomes part of a system or structure that lend their particular qualities to the whole group.

I'd doubt a tube will hold much pressure at all by itself. But I'd be happy to be surprised if anyone wants to make balloons of their tubes..
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Old 10-02-21, 08:56 AM
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This thread discusses the pressure needed to burst a balloon. It takes a pressure of about 75mm of Hg to burst the balloons. That’s 1.5 psi. Of course a balloon is thinner but I doubt that you’ll have much more pressure in a tire tube before it bursts. It just expands more. I’d estimate 5 psi or less.
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Old 10-02-21, 10:44 AM
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I get a pretty big number back-envelope but it does not account for the hernia so Iím pretty sure itís not right. At my job we use water for pressure tests most of the time unless itís too heavy. The energy stored is much lower because itís not compressible. Try it! Have fun! Itís very unlikely to kill you.

I predict failure at the stress concentration at the valve or any patches

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Old 10-02-21, 01:16 PM
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The pressure and strain in a balloon made of a material that can stretch 500% or more before yield seems like it would be a good homework problem for a college structures class. Maybe discipline-specific. I can't recall such a one but we were concentrating on fuel tanks and cabins and spars and combustion chambers, all rigid material
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Old 10-02-21, 01:23 PM
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Old 10-02-21, 01:32 PM
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Although come to think about it more, maybe it's higher than I expected. I did several years ago get a sidewall cut while out riding. The wheel immediately made a loud bang and was instantly flat.

Changed out the tube with new and then inflated the tube with CO2. A part of the tube came out of the 1/4" sidewall cut in a bubble the size of a dime and held. I figure the it must have been about 75 psi or better in the tube. It didn't blow so I just let some pressure out and it went back in the tire. I stuck a piece of something in there to act like a boot and rode it home and then put a new tire on.

But even if a tube not in a tire will take a lot of PSI, the tube will probably be stretched to the size of those old truck tire inner tubes I use to float down the creek on..
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Old 10-02-21, 08:45 PM
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Originally Posted by Iride01 View Post
But even if a tube not in a tire will take a lot of PSI, the tube will probably be stretched to the size of those old truck tire inner tubes I use to float down the creek on..
I used to let my young daughter pump up old tubes for fun - they'd get almost as big as the whole garage before they finally let loose... not a bang, just a poof. Lot of volume, not much pressure.

Last edited by DiabloScott; 10-02-21 at 08:49 PM.
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Old 10-02-21, 09:12 PM
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Sometimes when I was fixing a puncture and couldn't locate the hole, I inflated the tube a bit more past its normal size and it developed a bulge in one spot before it would overall get much bigger and it was clear it would burst on that bubble, so I didn't continue. Maybe these days, the tubes are made with some more exacting process so their wall thickness doesn't vary too much and they can be inflated much more but I didn't have intractable flat for ages, so.

Now, it you asked how much pressure before tube inside tire would burst... I guess here I would put on my protective glasses and even then I wouldn't like that. I know that with automotive tires, people got killed mishandling tire job.
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Old 10-02-21, 09:14 PM
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Some have already alluded to measuring low pressures with water. That is my suggestion.

You can make a pretty simple low pressure tester with a few pipes or hose. The measuring side, at least, needs to be clear so you can see the water level. Set up the tube/pipe structure as a U. On one side route the pressure line to also get pressure in to the U. The other side mark increments in inches, maybe even 1/4 or 1/8" depending on how precise you want to get. Fill the U with water up to your set point (0 line). Apply pressure on the pressure end. As you apply pressure the water level in the measuring side will rise. Just make sure that the surface area that the pressure is applied to is the same surface area as the measuring side. That would be the inside diameter of the pipe/hose/tube is the same. Where the bottom of the U is doesn't matter, so long as the pipe/tube/hose above the lowest point the water will be pushed to on the pressure side, and the tube above the 0 point on the measuring side, are the same. Therefore, you can do this with very small tube - even 1/4" tube to keep it cheap. Keep the U set up perfectly vertical.

14" WC = 1/2 PSI, roughly. WC = water column.
27-3/4" WC = 1 PSI
138-1/2" WC = 5 PSI

Inches of water column is a common unit of measure for low pressure natural gas (like in your house). You can get manometers that measure these low pressures, if ya want to get fancy with it. You have to check the measurement ranges carefully as most have specific pressure ranges that they work within. Too low of a max pressure and you'll break it, too high of a max pressure and you won't get the resolution on lower pressures. So you should have a starting idea of where your pressure is going to be so you can try and get that pressure in the resolution range of the meter.

On edit - if you scale the input pressure line with surface area you can compute the difference of - say it is exactly 1/2 the surface area of the measuring side - then you can cut the length in half of the measuring side that you would need. The increments would be 1/2" = 1" though. You could use any scaling you wanted, but if you get off of a standard fraction the gradation of the measuring side would be a lot harder to accurately mark.

Last edited by KC8QVO; 10-02-21 at 09:28 PM.
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Old 10-11-21, 05:48 PM
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Call it a hernia or an aneurysm. A bulge in an inner tube. The bulge is very taut, the rest is very squishy. it holds air so it will work just fine installed in a tire.

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Old 10-11-21, 11:23 PM
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If you have that inside a tire like with a too undersize tube it will burst on a puncture rather than just leaking and itíll be hard or impossible to patch.
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Old 10-12-21, 09:57 AM
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Originally Posted by 10 Wheels View Post
Why would someone do that?
In search of the elusive michelin flat microscopic pinhole out on the road comes to mind. Or heck, in the bathroom when I'm trying to find it with water in the sink and have spun the tube through the water twice at what feels like an already-overinflated tube. (But for the latter, I at least have the knowledge that if I blow a tube by more pumping, the tube was still no good to me anyway without finding the leak.)
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Old 10-12-21, 10:15 AM
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The gauge on my pump appears to read down to 10psi, and the needle is moving in response to changes in air pressure a few PSI below that, but I can't begin to guess how accurate it is. I use it for my fat bike tires which I inflate up to around (what I think is likely) the 8 psi mark then, going by feel, let some air out over the first ride after inflation.
Blowing an unconstrained tube up to the point where it ruptures barely makes the needle of my pump move off of zero. My guess is less than 5psi.
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Old 10-12-21, 10:34 AM
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I believe it would take less pump psi to burst the tube when in Denver (ambient psi is 12.15) as compared to sea level (14.7 psi), and even less at the summit of Mt Everest (4.5 psi), and might take around 9,000 psi at full ocean depth, yes? Someone has to test this theory, any takers?

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Old 10-12-21, 10:37 AM
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Originally Posted by Riveting View Post
I believe it would take takes less pump psi to burst the tube when in Denver (ambient is 12.15 psi) as compared to sea level (14.7 psi), and even less at the summit of Mt Everest (4.5 psi), yes?
The real test will be to count how many strokes to burst a tube at the bottom of the Mariana Trench, and how many on the moon.
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Old 10-12-21, 10:50 AM
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Originally Posted by ClydeClydeson View Post
The real test will be to count how many strokes to burst a tube at the bottom of the Mariana Trench, and how many on the moon.
But only if your floor pump is rated to 9,000+ psi. I've worked in a facility where we pressure tested equipment meant for full ocean depth up to 10,000psi, and have seen 10" diameter, 3/8" thick, titanium tubes collapse and shatter at a lot less.
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