# Cargo Actual Diameter at Pressure

We were wondering what other teams cargo diameter is at correct pressure. Ours is measuring about 9 1/4". Currently we’re still waiting for our pressure gauge to come in, but have filled the cargo up until it’s definitely over pressurized and it doesn’t seem to be growing any larger.

I thought it’s weird that the manual says the cargo is 9 1/2" instead of ~ 9 1/2".

Section 5.7
CARGO is 9½ in. (~24 cm) in diameter, weighs 9½ oz. (~270 g), and has a fuzz surface.
CARGO is inflated to 3½ psi. ±½ psi.

What diameter are you guys getting with your cargo?

All the cargo I have measured has been 9.25ish. Granted we only have 2 currently. Waiting on more.

yup, 9.25" diameter, and it doesn’t change appreciably with pressure, past about 2psi

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Have you seen any expansion of similar inflated game pieces in previous years as they get used throughout competition?

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I can’t recall any similar game pieces. The closest might be 2010. The rubber balls with very elastic skin, as used in 2019, and the large balls with a cloth bag around an elastic bladder in 2008-2014, are not really the same as the 2022 game piece.

As I’ve been told many times after learning the hard way in 2020. Design around the variations (different psi and worn out game pieces). I dont have much confidence in the pressure gauge regulation at events, and I’ll bet it’ll vary from event to event.

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Stupid question I should know the answer to, but don’t have a complex enough mental model.

Would atmospheric pressure at different alititudes come into play here?

Or, maybe asked differently… does the spec’ed inflation PSI refer to some absolute measurement that won’t vary as altitude/weather changes, or is it relative to outside atmospheric pressure?

I really feel like I should know this answer, but I’m drawing a blank on how to even think about it.

good question…I can take a wild guess.

If the ball is elastic, then it will expand when going to a higher elevation (lower atmospheric pressure). The gauge pressure may not change much.

If the ball is inelastic, then the absolute pressure in the ball will stay the same, but atmospheric pressure will drop with increased elevation, so the gauge should read higher. The spec’d pressure is a relative pressure reading. So when you bring a ball from your home in San Diego, to play in Denver, you’ll need to let some air out. And reinflate it when you get back home.

But that’s only my wild guess, from watching thin plastic water bottles as I drive to lower elevations all the time.

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Going off what the user in this post explained, it sounds like it most certainly would/will.

Definitely the rule means gauge pressure, that is, the pressure in excess of local atmospheric pressure. 3½ psi absolute pressure would cause the CARGO to collapse into a bowl shape at sea level.

We are just trying to figure out how much variation to account for. At this point I would think cargo would mostly be shrinking due to lowering pressure. If it doesn’t grow much past 2 psi, then I would think they won’t over expand much throughout the competition.

We’re getting +/- 0.25"

Also, we intentionally inflated one to 10 psi for over a week now. Still only ~0.25" larger than the normal ball. It does have a noticeable firmness to it and it bounces about 6-8" higher with the test drop.

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Are you saying yours are 9.5" +/- .25"?

Understandable. Based on my observations so far, the variation in the ball due to change in psi, isnt remotely close to what happened to the yellow balls in 2020 as it got damaged and shrunk over time.

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I just measured a ball that we purchased from AndyMark that is inflated to about 3.5 psi and bounces within the prescribed parameters. It’s almost exactly 9.5". I’m at 200 feet above sea level.

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We got our pressure gauge today and filled one of the cargo balls to pressure. I noticed when measuring it this time that it’s not perfectly round. Not that I’m surprised by this, but just thought it would be good to mention. This could be why some people are getting different diameters. To measure ours I set it on a table and used a height gauge. I was getting heights from 9.20" to 9.40".

Also FYI, in the manual for the digital gauge we got, it has you zero the pressure first so that it’s set for you altitude.

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We aired some up today and a significant portion weren’t round. 1/3 to 1/2 I think.

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