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My man Marc just posted this awesome build of the Compressed Air Rocket kit, which looks like a perfect summer project with the kids. When he got to the part about wrapping the PVC in duct tape for safety I had flashbacks of the Burrito Blaster build we did on Make: television; we debated back and forth whether or not to wrap it in duct tape.

This being the internet, there are lots of people with strong opinions about the matter. Some say that the duct tape is necessary to contain the shrapnel, in case the PVC should burst. Others say the duct tape will be of no use whatsoever. Still others point out that protecting the PVC from UV light will prolong its life. I personally was satisfied with getting Bill Gurstelle‘s word that in his years of backyard ballistics, he’s never seen a single accident where a properly used air cannon’s PVC chamber exploded.

So this is my question: based on experience, rather than theory, can anyone definitively say if duct tape wrapped around a PVC air chamber improves the safety of these devices? Please let us know in the comments. And if you shoot some video of your experiment, we all want to see it!

John Edgar Park

John Edgar Park

John Edgar Park likes to make things and tell people about it. He works at Disney Research and writes for Make and Boing Boing. He is training for American Ninja Warrior. You can find him at and twitter @johnedgarpark — if you like that sort of thing.

  • SKR

    I don’t know about the shrapnel, but UV light will degrade PVC. Covering it would help protect it from UV, but so would painting it. IIRC, I saw a Discovery Channel program where they showed stress tests on PVC. One was pressure. The PVC bulged in a very elastic way before exploding. I’m guessing that if it starts bulging, run. Or maybe vent the gas.

  • ssummers

    We had the same theory about the tape reinforcement. we however used the fiber reinforced packing tape to shore up our potato cannon. I’ll never exactly know the physics and pressures involved but we had a malfunction and instead of rupturing the “reinforced” chamber it blew off the 6 inch sewer cleanout fitting at the end. The cleanout had been applied with primer and pvc glue and still ended up being the weak spot. The cleanout blew a hole thought the siding of the house and was lodged inside. Spectacular. I dont wonder if the tape might make a pressure vessel go from sparkler to sparkler bomb in the event of a failure.

  • What

    When building a high pressure container out of PVC duct tape is always a good idea, in the process of building the last aircannon I messed around with I used some PVC cement that I have had for years…well, its effectiveness had significantly decreased and I had the glue joint fail between the chamber and the cap on one end. The end cap bounced off the lawn and created a ~2″ deep impression in fairly hard soil…

    It cant hurt to add in a second layer of safety to a project, it *does* hurt when a PVC endcap ricochets into your face… =?

  • Paul

    Anecdotal experience is really of no use to us here.

    What you really need to do is some rigorous testing, causing both tape wrapped and unwrapped chambers to fail.

    Of course you’ll want to record the results on video & take all the necessary precautions to make sure you don’t end up with pvc shards in the eye, or embedded in your skin.

    Really, with the number of makers coming to, and duplicating many of your PVC based projects, you’d be poor netizens if you didn’t do this experiment.


    • pdub

      Anecdotal evidence may not fall into the realm of ‘true’ scientific experiments, but it is still valid in many ways. True, there is no control group, but there is a large bastion of makers recreating these steps and having valid results to comment upon. This is a vast resource from which to glean equally vast amounts of knowledge. Let’s get away from the scare tactics (which are valid from time to time) and check out what people are really doing in their backyards. We can have safety and fun at the same time!!

      -Paul, alias pdub

      • Paul

        Well, my only “scare tactics” were in encouraging someone doing these tests to hide in a bunker during the tests…

        Really I just wanted to see a mythbuster style video, complete with John Park and Philip Torrone doing a countdown from inside a bunker made out of plywood and a couple of doors with safety glass. Bonus points if the bunker really does get buried so that it’s just peeking above the ground.

        Needed for testing the PVC? Not at all.

        Worth it for the entertainment factor? I think so.

        So, how do we talk them into this?


        • pdub

          Wasn’t trying to be a jerk. Sorry, my friend.

          I agree with the mythbusters theme. How can we bring this to their attention?

          • Paul

            Didn’t come across that way at all.

  • Desco

    You’re probably going to blow the 1/16″ thin rubber hose or one of the fittings LOOONG before you blow the PVC itself.

  • NMA

    It takes much less pressure than you might think (than I thought) to turn a PVC pipe into flying shrapnel. Precautionary measures are definitely warranted. In retrospect, it would have been preferable to have the end cap fail before the pipe. At least you can point it away from yourself…

    • Marc de Vinck

      That is what I was thinking when it comes to the air rockets. I would think the tube from the pump is more likely to come flying off the brass connector, rather than the PVC exploding? (although I still wrapped the chamber in tape!)

      Looking forward to some tests?!

  • Emilio

    we have a Mythbusters episode in the making.

  • clide

    There are a few tests that have been done by spud-gunning enthusiasts with regards to this. Not much about whether it will increase the strength or not, but common sense should tell you that you don’t want to rely on any reasonable amount of duct tape to increase the strength of your pressure vessel.

    The first was done a long time ago. A guy had a steel box and oxygen and acetylene to induce failure in a PVC air chamber by over pressurizing the pipe. He tested various coverings including duct tape, blue jeans, and chicken wire. A failing PVC chamber ripped apart all of the materials, they were useless at containing PVC shrapnel.

    Another test, still able to be seen through the Way Back Machine shows a test where failure was induced with a low power gun. Duct tape did nothing to contain the shrapnel.

    Duct tape will provide some protection from UV and some minimal impact protection, but if either of those is a concern there is better protection available.

    That being said, there are several things to look out for when building a PVC pressure vessel. Always use pressure rated pipe and fittings. Cheap sewer fittings like clean-out adapters are the most common cause of failure. It is also a good idea to stay below half the rated pressure. They are rated for water not air; same forces but there is a lot more danger involved when it fails with air pressure. Learn to properly solvent weld PVC, there are tons of free tutorials on the internet. Avoid stressing the fittings with recoil or a strange configuration. The fittings are designed for internal pressure and trying to bend or torque a fitting can easily cause it to break. If you are using a high pressure gas supply like CO2 then always include a pressure relief valve, regulators can get stuck.

    • Desco

      As cool as these tests sound, this test is concerned with the EXPLOSIVE forces of a potato gun using an ignited fuel/air mix, not the slow expanding force of compressed air, as the OP mentioned. So while these tests do apply to potato guns, it may not necessarily have the same results acting as an air tank.

      • clide

        The failure characteristic of PVC is going to be extremely similar no matter how fast the pressure rises. The explosion in the second test was caused by static air pressure, the failure was simply induced by a sharp impact.

        PVC is quite rigid and expands very little before a catastrophic failure. Duct tape is a lot stretchier than PVC and I would be surprised if it provided any statistically significant increase in failure point.

  • Wilson!

    Another factor in all this is the adhesive on the tape. Does the adhesive in duct tape react in some way with PVC? I know my kid’s bicycle helmet came with stickers, but if you read the instructions (who does that anymore?) it says not to put any kind of sticker on the helmet, as it might weaken it. So the duct tape might actually be weakening the pressure vessel…

    We definitely need the MythBusters to tackle this one!!!

  • netmaster

    The only recent real-world testing of PVC I’ve run across is this This test dealt mainly with PVC failure via impact and at different temperatures. Very well done for backyard stuff.

    I use 2″ PVC on my pneumatic net gun, and the only failure I’ve had was impact related. The pressurized gun fell off my deck railing (stupid place to put it, I deserved it), the only piece that broke off was the pressure gauge with a bit of PVC stuck to it.

    I think you should concentrate on what is the worst case *likely* failure scenario. Don’t do a gee whiz experiment where you use a Scuba tank to take 2″ PVC to 500 psi. I think what needs to be answered is what type of degradation (extended UV exposure, temperature extremes, impact, etc.) will make PVC burst at around 80-120psi (the amount most DIY compressors can realistically achieve). And when failure occurs will tape have any effect?

    You also have to classify what type of failure you are trying to analyze. Are you trying to prevent all the little sharp shrapnel pieces d from the pipe from flying about? Or are you trying to prevent the heavy 2″ end cap (or valve, or coupler) from getting launched?

    My hypothesis would be that frigidly cold pipe could have a shatter type failure, and that a layer of tape would mitigate getting a face full of PVC shrapnel. I am not sure, on the other hand, how well tape would prevent large heavy components (valves, couplers, end caps) from being launched into your neighbors yard, or through your drywall.

    My most recent net gun I made the pressure chamber from all couplers, no pipe is exposed anywhere.

  • Alan Parekh

    I think this calls for a Mythbusters like test to solve the mystery once and for all. I can’t see the tape harming the pipe and it’s sure to protect it from the UV present in sunlight but my gut is telling me that there will be no dramatic benefit. We need to borrow the old shipping container that Mythbusters has to test the rupture point though.

  • Ryan O’Horo

    When I built my largest PVC cannon I wrapped the tank in a single layer of chicken wire then a cotton fabric blanket. It fit right into the inset the endcaps made. This seemed like the most sensible way to contain and reduce velocity of escaping shrapnel. If anything, I’d imagine that duct taping your cannon gives a false sends of security and will encourage over-pressurizing your storage tanks.

  • Paul

    Rather than trying to deal with the catastrophic failure of the pvc (catastrophic for the device, not us) couldn’t we just add a failure point?

    Like, maybe a 75 pound pressure release valve (or is that too high?)

    A quick search brought them up at about $21 a piece, so it significantly increases the cost, but I’m just throwing that out as a starting point.

    • Ryan O’Horo

      Ah yes, I guess I should have also mentioned that all of my projects include a relief valve (they even sell them at Home Depot) no exceptions. But these also fail.

      • Paul

        Yikes, having the “safety mechanism” fail is a bit unsettling. I guess that’s why you also wrap the tank.

        Any sense on whether the relief valves truly failed (stayed closed above their rated pressure/time) or if something else just failed first?

    • Toaste

      I think knowing the point of fail is the best way to make these safer.

      What about drilling a hole in the end cap and covering it with paper? Experiment with the blowout pressure of the endcap alone, then try 1/2″ hole with tissue, paper, and cardboard.

      Finding the best material (high repeatability for the pressure where the paper pops and vents the chamber, wide margin of safety, sufficient pressure for the application at hand) might require some experiments, but it should be fun to test when stuff blows up.

  • Apis

    Hmm, as the first posts indicate the point of failure is probably going to be a smaller part being propelled away by the pressure, and that projectile is probably a lot more dangerous than an exploding pvc vessel (although less dramatic perhaps).

  • Kevin Fodor

    I don’t know how safe PVC is in this kind of application. I havn’t had any bad experiences myself, but when I set out to make my own Compressed Air Rocket Launcher I played o the safe side and decided to use black gas pipe. Yeah, I know…overkill for sure. But with my 5 year old son standing by at each launch I figured better be safe than sorry. I don’t think I could do anything to this arrangement to blow it up.

    More details at;

  • Boogieman

    There is actually evidence that the adhesives soften the PVC and make it weaker.
    There have been several band members hurt by ‘properly used’ air chambers. The band Arcainium was the most recent.,d.b2k

    There is not ONE manufacturer of PVC pipe that doesn’t state it is unsafe for use with Compressed gas
    OSHA states PVC is “banned” for use with compressed gas since 1970.
    In 2005 all major PB insurers banned the use of “homemade” launchers do to 5 recorded cases of them (PVC air chambers) exploding on the fields in 2004

    Arkansaw Razorback’s intern injured by exploding PVC TShirt Cannon.,d.b2k