5 ms·
These sorts of failures are usually caused by people constructing the potato cannon out of thinner schedule 40 PVC (usually colored white). If you use schedule
by ggreer 2y ago
These sorts of failures are usually caused by people constructing the potato cannon out of thinner schedule 40 PVC (usually colored white). If you use schedule 80 PVC (which tends to be dark gray) or ABS (which deforms instead of shattering), the risk is negligible.
This is also why I prefer pneumatic cannons to combustion. Since there's not a quick spike in pressure from a combustion reaction, the maximum pressure that needs to be contained is lower (and you can measure it with a gauge as you're pumping the air tank up). Also if you make the air tank big enough, the pressure behind the projectile stays high for longer, so you tend to get higher velocities.
When I was in high school I made a potato cannon, played around with it in the woods with some friends, and then told my parents about it. My mom wasn't too happy, but my dad took it as a challenge. He built an even more powerful pneumatic version with a tripod, sights, and a solenoid trigger mechanism. The whole family loved it. I used some extra PVC pipe to make molds for cement slugs. With a little paper wadding to get a good seal, they'd go fast enough to embed themselves a couple feet into the side of a hill. It was spectacular.
- ryandrake 2y agoYea, Home Depot PVC doesn't belong anywhere near compressed air. I knew a guy who wanted to outfit his garage with several compressed air drops for air tools and used plain old white PVC. Big mistake which he realized when one of the fittings shattered and launched a metal quick-disconnect through the garage door and out into the street. Thankfully nobody was in the line of fire. Please don't use PVC for air under pressure.
- jvanderbot 2y agoId love to make more potato cannons but my main issue is exactly this. I have no idea what the pressures are, what materials would work, etc. It's all folklore and bravery
- doubleg72 2y agoNot really.. you can find standard ratings for pipes all over the place. I just ran air lines in my garage and it was fairly simple for me to get online and see that I needed type m copper based on the pressure I'm at. Wasn't cheap, but neither is aluminum pipe and now i have a nice reel in the center of the garage. There's a bit more to calculating the pressure when exploding hairspray in an enclosed vessel, but I'd be willing to bet just as easy information to find.
- memcg 2y agoI worked in a PCB shop that had a network of 1 1/2" PVC pipe for compressed air. When Tees failed we would lose production for the remainder of the day. We finally replaced the entire network with type M copper.
- metadat 2y agoMaybe wrap it in a ton of duct tape, then it can't shatter too dangerously.
- tyingq 2y agoDepending on the circumstances, that can also make it a more powerful bomb.
- metadat 2y agoHrm :-/ okay, please disregard.
- tetris11 2y agowhat if you house it in a pool of acid, and place it near a baby for safety
- jvanderbot 2y agoAgain - neither of these are much more than moderately held opinions.
- tyingq 2y agoThat strengthening a pressure vessel with tape might raise the pressure at which it fails? Does that really need a citation? One example: https://www.cbsnews.com/news/texas-teen-gravely-injured-by-homemade-sparkler-bomb/ https://www.cbsnews.com/news/texas-teen-gravely-injured-by-h...
- jvanderbot 2y agoWell there's two of many possible outcomes, which are covered under your "depending on the circumstances", which make your comment universally true, and therefore not so informative: 1. We strengthen the pressure vessel enough so that it gives way at higher pressure, making a "stronger bomb" 2. We strengthen the pressure vessel enough so that it doesn't give way, making it not a bomb at all. It's not at all clear if the duct tape will do 1 or 2 or something else, and this first-order logic / first-impressions design doesn't smell to me like a rigorous solution.
- MisterTea 2y agoThen use steel or aluminum pipe.
- arwineap 2y agoHome Depot sells many grades of PVC and pipe, it's up to the buyer to select the grade they need for their application. This is something I would suggest buyers do at every store they shop at.
- jvanderbot 2y agoHow do you know the risk is negligible?
- metadat 2y agoBecause it will fail earlier and less dramatically compared to a sudden increase which can explode violently.
- 0x0000000 2y ago> This is also why I prefer pneumatic cannons to combustion Strange, since combustion based cannons tend to reach about 30 to 40 psi at most, while pneumatic easily can reach 100 psi.
- lazide 2y agoCite? Butane and propane can easily produce > 100 psi when used in engines, and are commonly used as replacement for gasoline and other hydrocarbons in generators and fork lifts to do just that. In a confined enclosure (potato gets stuck or the like), it’s a pipe bomb.
- grogenaut 2y agoby engines I'm assuming you mean something with a stroking piston which is going to reduce the total volume by somewhere from 4:1 to 13:1, so that's going to increase major pis increases by itself even before explosion. You don't have compression with butane into a potato gun, just the efffects of the rapid combustion. So it wouldn't really be a fair comparison.
- lazide 2y agoHere is a nice declassified paper on using butane and propane in unconfined fuel air explosives. [https://apps.dtic.mil/sti/tr/pdf/ADA084367.pdf https://apps.dtic.mil/sti/tr/pdf/ADA084367.pdf] Quite effectively too. There is also some nice research on proper high explosive detonation of similar mixes when using proper detonators. It requires rather extreme amount of willful ignorance to think lighting a mixture of oxygen and butane or propane inside a enclosed space is only going to be 30-40 psi maximum, instead of ‘thank god it only hit that maybe because the potato moved’. [https://colab.ws/articles/10.1134/s0010508211010114 https://colab.ws/articles/10.1134/s0010508211010114] There was a good research paper I found that had a quantified set of numbers, but it required paying for it. Meh. Still waiting for that cite.
- fkyoureadthedoc 2y ago
- tyingq 2y agoNot leaving it outdoors probably helps also. PVC in the sun gets brittle.