An Interesting HPA Failure

I got some pics today of an imploded plenum spacer that was between a regulator and valve in a Disco.... Here is a side view, the pellet is to keep it from rolling over....

http://i378.photobucket.com/albums/o...psskddnol3.jpg

Here is the other side after a few shots.... The velocity dropped by over 400 fps in about 3 shots as this happened....

http://i378.photobucket.com/albums/o...psojmxqssy.jpg

End view, showing the imploded section is stretched all the way across the ID of the tube.... Note how a small portion of the circumference of the wall has extruded to about twice it's original width....

http://i378.photobucket.com/albums/o...pstjs42d6h.jpg

Another view of this puzzling failure.... It would appear that the material is about 1/32" wall aluminium tubing....

http://i378.photobucket.com/albums/o...psivm9fkay.jpg


I think the initial failure was probably a small buckle failure of the tube wall from end compression, combined with a small amount of air in the space between the spacer and the reservoir wall.... Once it collapsed even slightly (the initial collapse may have only moved the wall in 1/32" or so), it had a larger volume of HPA behind it for the next shot, and imploded slightly.... That now much larger space then filled with HPA and on the next shot the much larger volume then expanded and extruded the wall inwards, stretching it into the current shape.... If you look at how much of the tube wall has stretched into the much longer length of the folded in portion, the wall must now be very thin.... One more shot would likely have ruptured it....

When I first heard about this "implosion" I thought it unlikely and suspected to see a buckle failure in the tube wall when I got the photos, but in fact the spacer was within about 1/16" of it's original length.... It would still slide out of the Disco reservoir.... I am not sure of the regulator setpoint, but if we assume it was 1500 psi, the end force on the tube spacer was about 650 lbs. when the reservoir was full, and would have increased during the shot cycle as the pressure in the plenum dropped.... There would not have been much volume of air initially between the spacer and the reservoir wall, but enough that combined with the end load it likely caused an initial buckle failure which then filled with air, and within a few shots imploded the tube spacer to produce the results shown.... It certainly shows the power of HPA, and how completely unexpected things can happen....

Bob