Ever wonder how strong an airtube really is?

[Hajimoto]

"AirGunShooter"

"Hajimoto"

"AirGunShooter"Hajimoto - Have you ever performed a hoop stress calculation on an air gun pressure tube to determine the allowable pressure at the material's stated yield strength?

No sir I personally have not. Sorry
It was just curios if you were in any way involved with the pressure test video?
Early in the video when tube diameter measurements were taken after the first pressure cycle and it was noted the change in diameter, the material had already yielded. When designing and working with high pressure materials to be used with a compressible fluid, we consider a yield of this magnitude to be a material failure. Any time an item is stressed to the point of exceeding the specified minimum yield strength of that material, the item has officially failed. Testing to ultimate catastrophic failure is certainly important, but it is not a point I would ever want to use in the real world safety design rating of a product. Hopefully those doing the video performed a calculated yield point to use for predicting material failure and fatigue related cycles. 

SO I asked the testing group and posted your concerns. This is the response I received back.

"Sure, I will be happy to address that comment, and it is a good comment. A couple of hours of video was edited to produce the two videos of a few minutes each. Numerous measurements were taken throughout the testing that are not shown on the videos.
The yield calculation for the tube predict material yield to start at approximately 8500psi. Yield is normally taken as a 0.2 percent permanent deformation of the tube. After the 9,000 psi o-ring failure, the deformation was measured as being 0.002" on the diameter, or about 0.16 percent, so still barely below the yield definition. Based on that measurement, one could say that yield had started and that failure had occurred. However, as the pressurization continued, the growth remained rather insignificant, as determined by measurements, and also by observation of the minimal amount of oil that was pumped into the tube. The increase in oil volume did not really occur until about 10,000 psi, when yield and resulting elongation were fully underway. Full failure occurred at 10,000 psi.

You could say that yield had started at 9,000 psi, which would be a 3 to one safety factor for yield. Final failure was at 10,000psi, or a 3.3 to one safety factor.
Those two numbers represent good, solid safety factors for a small pressure vessel.

Required safety factors vary by certifying organization with the yield safety factor always being lower than the ultimate failure safety factor. Bob Sterne has researched the various trends in safety factors, and I hope he will chime in. As I said, suggested/required safety factors vary by organization, and even year to year within some organizations.

Again, a 3 to 1 safety factor for yield is, I believe, satisfactory and safe."

I understand his clarifications and feel comfortable with the purchase once again.... WHEW!