SpudFiles

Oxbreath wrote:nothing you can do will make it completely failsafe.

If it works at all, and students have or can gain access to it, without supervision... I guarantee that some student is going to find a way to cause a fail.

The only way to make this truly failsafe, is to not use it at all.

This.

As they say, you can make something foolproof, but somebody keeps making better fools.

If you're using rated parts and keeping below their recommended pressures (which are there for this very reason), you have nothing to worry about, unless you attack the thing with a hammer while it's at pressure (see: foolproof).

In my experience, most people on this forum will strongly encourage ample safety with launchers, but there is a point of diminishing returns. Your earlier comment "I am not interested in your opinion about whether the launcher is safe at my current pressure", sounds like a large double standard to me considering you are asking the same people for help on making the gun "failsafe".

Your biggest concern with a rupture would be a result of throwing the gun while it's at pressure. You could perhaps build a spacer ring or two around the tank itself to absorb any accidental impact. The same way that propane tanks at service stations have bollards around them to stop cars driving into them.

There are 3 parts to any successful safety program.

They are Engineering controls. This places a barrier between a hazard and the people. Safety guards, interlocked elevator doors and such are Engineering controls.

Technical Controls. This ensures the integrity of the system. Technical controls are such things as rated metal vessels and pressure rated parts for air systems. Safety pop off valves. Laminated widshield glass instead of single pane glass.

The most important is Administrative Safety controls.. This is the administration of safety policy. This includes wearing PPE such as gloves and safety glasses, keeping the muzzle pointed downrange at all times, nobody crosses the firing line, using handrails in stairways, etc, obeying speed limits, stopping for red lights and stop signs, no drinking while operating, etc.. Behavior is the cause of most safety failures.

Use all 3 for a safe launcher.

I will ever so slightly disagree with the majority of this thread. While PVC parts are exeedingly unlikely to fail due to the forces a well designed cannon will put on them, the risk of failure from dropping the thing when pressurised is a real danger.

If I were you, I would simply build the whole launcher out of metal. Most metal fittings and pipes will take stresses several orders of magnitude above what the cannon will normally see, without any damage at all. If you build it from a material like this, there is practically nothing you could do that would cause a failure, short of taking a hacksaw to it. No need for additional enclosures or padding, and you can have complete confidence it will be safe.

katypotaty wrote:My question concerns making the gun failsafe.

Throw the gun away and make another one out of steel.

Problem solved.

D_Hall wrote:Problem solved.

LOL, Jack, one of the first youtube links you post that made me lawl.

First off, have you taken a look at your pressure rated PVC pipe? If you have, you'll probably see that you shouldn't use PVC for pressurized gas in any situation emblazoned across the side in some way. That may lead you to ask why we use it (its because its cheap available, and tested), but you're situation puts it in a situation where it may be prone to abuse, and failure would indefinitely result in legal action. Now lets say you wrap it in fiberglass and encase it in ABS, in the event of failure, a prosecutor would have a field day finding a hunk of plastic stuck in some kid's leg with the words:
"---------------------------WARNING----------------------------
Never use plastic pipe fittings with compressed air or gas."
written clearly across the side.

I build with PVC all the time, but I use it safely, carefully, and if it explodes I'm the only one at any risk. If you are in this situation; metal fittings RATED for compressed GASSES is the only way to truly be safe

Some plastics is rated for compressed gas use. The problem is it is not rigid. Natural gas is delivered in PE pipe.

Pressure rated plastic pipe for gas;
http://www.alibaba.com/product-gs/35743 ... l_gas.html

D_Hall wrote: Throw the gun away and make another one out of steel.

Problem solved.

Not really. "Steel", particularly if it isn't designed for a pressure application, is no more a 100% guarantee against failure than is a properly designed plastic gun. A steel gun made from a suitable steel and designed and assembled correctly would be better than a typical PVC gun.

The only "failsafe" gun is one that is never built. The major risk with any gun isn't failure of the material it is failure to use it safely. I've never heard of a person hurt by a real gun failing (though I';m sure it happens occasionally). I have often heard of people that "should know better" (like cops) shooting themselves in the foot.

jimmy101 wrote:I've never heard of a person hurt by a real gun failing (though I'm sure it happens occasionally).

Google the name of a popular firearm model/manufacturer (eg Glock, 1911 etc.) along with the word "kaboom", you'll be surprised!

Yep, it happens..



Often through abuse though..

Still, my point was that locally, at least once a month or so, someone is hurt by doing something stupid with a gun. Occasionally, as in perhaps a couple times a year someone somehere in the world is hurt by a mechanical failure of a gun.

Chances of getting hurt by the failure of a commercial gun is probably a lot less than the chances of getting hit by lightning or bitten by a shark.

Chances of getting hurt because you did something stupid with your gun is probably something like the chances of being in a car accident.

jimmy101 wrote:Occasionally, as in perhaps a couple times a year someone somehere in the world is hurt by a mechanical failure of a gun.

Well, either I completely defy the odds, or you're a little off the mark with that, as one of my relatives was not only injured but killed by the mechanical failure of a gun. Short version, its chamber blew apart, caused a major head wound which turned septic and killed him. Still, his death certificate lists "Gun barrel rupture" (or words to that effect) as the cause of death.

To be fair, this was over a hundred years ago, when materials science and engineering weren't what they are now; But even so, extrapolating a bit from the plethora of "Kaboom" pictures on the Firearm blog, I'd still say it's probably quite a bit more common than you're guessing.

... yet we seem to have scared the OP off

Decided he needed a safer hobby... tiddly winks perhaps?

But those little plastic discs could....knock the dust from your eyelash or some such.