Neer fatal disaster.

Tell stories about your spud cannon adventures!

Postby MarvinTheRobot » Sun Sep 19, 2004 3:53 pm

Today I had to run my generator (prep for winter,) and I decided to load test it with my compressor.
What better use for the air, than to lob 24ox pepsi bottles with my big in-line potatoe gun?

I had 2 sucessfull shots, and was re-chargine my 4" x 3' chamber, when BANG!!!
The 4" pvc endcap my shrader valve was in, catastrophicly failed.
My right hand was on the air chuck, filling the chamber to 120psi.

At the time of failure, the chamber was around 110psi, because the air had almost stopped flowing into the chamber.

The results:
Pieces of the endcap were found 100ft+ away from ground zero.
My thumb has a minor cut, but it is completely covered by a band-aid.
My middle and ring fingers middle knuckles are red, and have small streaks of blood across them.
All of my right hand fingers feel like they were hit with a hammer.
Ether the chuck or the valve hit me in the right side of my chest, leaving a "3rd nipple" :)
My spud gun is completely demolished, the force pushed it into the driveway, breaking it in several places

The gun: It was an in-line gun, about 1.5 years old.
I filled it with the barrel removed,, resting it vertically on the ground, so the endcap and schrader valve are pointing up.
Now it is in 2 main pieces, and the endcap is in fragments.

Pics:
<a href="http://www.fraggedhosting.com/imagehosting/public/P1050645.JPG">Image 1 (185K)</a>
<a href="http://www.fraggedhosting.com/imagehosting/public/P1050647.JPG">Image 2 (214K)</a>
<a href="http://www.fraggedhosting.com/imagehosting/public/P1050648.JPG">Image 3 (180K)</a>


<i>Next time use links for pictures that are that large. It kills people on dialup connections. (plasticex)</i>
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Postby plasticex009 » Sun Sep 19, 2004 4:18 pm

Did you previously drop this launcher or did any thing happen that could have weakened the endcap? That endcap looks different that the ones I have used; they have had a dome shaped end not a flat surface. I would venture to guess that the flat endcaps are not supposed to be used in pressurized systems just because of their shape. Recall that most pressure vessles have hemisperical ends.
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Postby MarvinTheRobot » Sun Sep 19, 2004 4:25 pm

It was sch40, so it was pressure rated, but in the future I am gonna revise my fill system :)
I have a feeling that it has been rested on the valve a few times, as I have a sibling, who is, shall we say, less than bright. :)
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Postby PCGUY » Sun Sep 19, 2004 4:58 pm

Just because something is SCH 40 doesn't mean it is pressure rated... it could say SCH-40 Cellular Core...
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Postby Mr.Plow » Sun Sep 19, 2004 5:33 pm

ditto plasticex.

I've seen the flat end ones, but they're all DWV.

I friend of mine two houses over had a basic combustion with one of those on it, and it failed as well. It wasn't what I'd call a "safe" cannon by ANY means (it was all cell core with DVW fittings, with a 1" hole in the side for spraying hairspray and sticking a long-stem lighter into...when I pointed out the safety concerns, he replied, "Its ok, thats why I covered the outside with duct tape!" [:o]). Funny how the endcap blew off before the cellcore went...
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Postby Rex_R » Sun Sep 19, 2004 5:35 pm

I believe that I read on mcmaster that sch40 endcaps(in 4") were not pressure rated, and that you had to go with sch80 if you wanted a pressure rated cap(preferably a slip cap)
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Postby plasticex009 » Sun Sep 19, 2004 5:37 pm

As PCGUY said, SCH40 doesn't mean it is rated for pressure. SCH40 is merely a dimensional standard, meaning that SCH40 3" pipe will fit into any SCH40 3" socket fitting.

It is like saying a 1/4"-20 nut will fit on a 1/4"-20 bolt. If you want to know how much stress the bolt/nut will hold, you can't judge this based off of the size alone, material properties must be accounted for.
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Postby buzzboy » Sun Sep 19, 2004 6:55 pm

Plus somebody soom in on pic one. The chamber says nsf-dwv. Not a good sign.

What type of schrader were you using. I use ones that have a rubber gasket on the insideand a nut on the outside. I don't see how you guys like the ones that screw into the chamber. This seems like it would make it even less safe.
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Postby ryno » Sun Sep 19, 2004 7:01 pm

<blockquote id="quote"><font size="1" face="tahoma,verdana,arial" id="quote">quote:<hr height="1" noshade id="quote">Originally posted by buzzboy
[br]Plus somebody soom in on pic one. The chamber says nsf-dwv. Not a good sign.
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
It may or may not be. On all of my pressure rated pipe, it also has nsf-dwv. It just means it can be used for it.
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Postby MarvinTheRobot » Mon Sep 20, 2004 1:05 pm

I'll tell you right now: EVERY PART HAD PRESSURE RATING! (above 175psi)

I use a metal schrader valve with a rubber gasket and a nut, it was chrome, and looked cool. :)

The problem was the fatuige it has suffered because it was rested on the valve often.
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