A Close Encounter: The Explosion of a Valve

[Velocity]

It was 53 degrees Fahrenheit at the time, about 8:40 PM. I decided I would shoot my <a href="http://www.spudfiles.com/forums/midsize ... mericannon Mini</a>, as it is my favorite spudgun that I have made. I took a ping-pong ball, injected it with water until it was filled, and loaded it into the cannon. I then setup a target outside, and brought the launcher outside. I attached it to my compressor, and filled it until the gauge read 30 PSI. The gauge on my universal filling system is broken, so it probably was not truly 30 PSI. However, my compressor is regulated down to 50 PSI, so unless that regulator was broken (which I highly doubt it was), the launcher had no more than 50 PSI in it.

I fired the ping-pong ball at the target (and I missed, low by about one foot), and a tremendous BOOM followed. I was surprised by the great noise created for only 30-50 PSI, but this cannon had always been loud, and so I was not worried. I then brought it inside, and placed it down on the carpet. When I went to shut the garage door, I noticed a large white scratch had developed on the side of my newly painted valve. Upon closer inspection, I realized that the valve had developed a large crack on the entire right side of the tee.

<img src="http://www.spudfiles.com/uploader/uploa ... ack333.JPG">

It is difficult to determine how this happened. It couldn't have been the temperature, because it was not that cold. It couldn't have been the pressure, because it was only 30-50 PSI. I believe that I did not have a sufficient bumper. I have an air hose coiled up inside of the metal bushing, but it does not extend past the edge of the bushing. There is one piece of foam rubber on the piston, hardly enough to stop the forces involved here. I think the piston slammed back, and the edge of the piston (a 2.5" piece of 1.875" type II PVC rod wrapped with some duct tape) hit the edge of the metal bushing. The bushing then was forced backward, and it pulled the PVC parts of the piston valve backwards, causing this huge crack to develop. The piston is unharmed (as far as I can tell).

I was holding the launcher by the chamber and the barrel at the time, and the valve was behind me. I am so very lucky that I was not holding any part of the valve, because that might have turned very ugly.

I am completely unhurt; I did not even realize that the launcher had failed until minutes after, when I saw the white crack on the black paint.

Some more pictures:
<a href="http://www.spudfiles.com/uploader/uploa ... PG">Female Adapter</a>
<a href="http://www.spudfiles.com/uploader/uploa ... 3.JPG">Top of the Valve</a>
<a href="http://www.spudfiles.com/uploader/uploa ... >Piston</a>
<a href="http://www.spudfiles.com/uploader/uploa ... PG">Inside the Valve</a>

While this might not have been a complete explosion that shattered the valve, the crack which runs through the valve shows that an incredible amount of force was present which caused the valve to break.

If anyone else has any insight on why this might have happened, I would appreciate it. I am just so thankful I came away with this with no injuries.

[PVC Arsenal 17]

Freaky! Must've gotten weak from being fired so much. Glad you're okay though.

How tight was the bushing screwed in? Looks like it could've expanded the fitting. That plus pressure might have done it in.

[pyromaniac]

Dang thats like the second time in a week that something exploded.

It's goos that your ok.

Really weird pictures.

[Velocity]

Thanks for your concerns everyone

Freaky! Must've gotten weak from being fired so much. Glad you're okay though.

How tight was the bushing screwed in? Looks like it could've expanded the fitting. That plus pressure might have done it in.

I don't think it got weak from firing so much (I do not shoot spudguns very often; this one was fired under 100 times so far). However, your theory regarding the bushing has made me think, and it is possible true. Anyone have an opinon on that?

Dang thats like the second time in a week that something exploded.

It's goos that your ok.

Really weird pictures.

I know that a couple of launchers have blown up recently. I think we should start a "Launcher Failure Log" sticky, like the one on the late Spudtech forums

Why are the pictures weird?

[clide]

My first instinct would be over tightening of the bushing. It may have been highly stressed already and the impact of the piston just pushed it over the edge. How much do you crank it down? I typically go one turn past hand tight.

I've also heard that using a male metal fitting in a plastic female makes it more prone to failure. I've had a female fitting crack before and IIRC I was screwing a metal bushing into it.

[joe blogs]

I had something like that happen to me. it turned out that the guy in the hardware store was an idiot and sold me the wrong pipe. I went back there and they didn't want me to complain to loudly so they found out who it was (turned out to be a trainee) and gave him a lecture and me a voucher for $50 but i wass still pissed because that incident could have been potentially deadly. The reason i didn't complain to higher authorities is that pneumatic guns are sort of illegal in Australia.

[frankrede]

You also used the pipe for a purpose of which it was designed.
That is your fault Joe Blogs, you should have checked the pipe yourself.

And Rmich, thats what I am thinking because I have broke fittings by over tightening them before,and that wasn't even with piton valve.

[Hawkeye]

I doubt Hardware store employees are trained to advise people on the correct pipe to buy for spudgun use. You should know what you are looking for before you go in and research what the labels mean.
Pretty much all of the material we use is technically the "wrong pipe" because none of it says "for spudgun use".

You don't expect the guy behind the Mcdonalds counter to be a nutrition expert, do you?

[VH_man]

Yeah, ive had metal fittings in plastic fittings fail on me beofre. just make sure you dont twist it too tight and youll be OK. if you can find a PVC part its proboably better, but whatever..... i dont think the bumper is a problem.

[Velocity]

Yeah, thats probably right... i tightened it as much as I could. I suppose I should only tighten it enough to prevent leaks, right?

I used to have a plastic plug, but I switched cause I didn't want the launcher to fail... funny how things work out, right

They should make NSF-sg (rated for spudguns )

So what do you think: when I rebuild this (ironically, I have been planning to rebuild this for weeks, and was going to order the parts tonight until the "incident" occurred), should I go with the plastic SCH 80 plug or steel?

[mega_swordman]

Dang thats like the second time in a week that something exploded.

It's goos that your ok.

I concur. This is certainly bizarre, lately there have been a large number of cannon accidents. Perhaps this means something, like with cannons becoming more sophisticated, people are becoming careless. Or I could be wrong and this could be a really bad coincidence or a "wave" of accidents that will eventually pass.

At the very least, you are alright. That's always good to hear.

[Hotwired]

Pressure pipe isn't meant to have shock loads put on it. It looks like the piston's finally managed to bash the metal fitting out, cracking the plastic as it went.

Lighter piston and more of a bumper next time?

I'd agree with a cannon failure log personally.

[jrrdw]

I beleave those metal plugs are made with a tapper to them, the futher you screw them in, the tighter they get. Sounds like a combination of wedgeing and the pressure assited, makeing the crack longer.

[lukemc]

glad to hear your ok it seems strang this happened after so long. do you have any pictures of the bumper you used?

[Kenny_McCormic]

i would get rid of the threads and use screws to hold a sch 80 cap on the back then it would be user seviceable and built like a tank