Half a croissant, on a plate, with a sign in front of it saying '50c'
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Dry ice potato gun

Easy build high pressure PVC potato gun
  (+7, -2)
(+7, -2)
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Simple. A strandard PVC spud gun barrel (2in PVC) attached to an electric sprinkler diaphram valve attached to enclosed PVC chamber. Inside said chamber is dry ice, submersied in water. As the CO 2 sublimes it builds up pressure inside the chamber, as read by standard pressure valve mounted on the outside. You load your starch projectile, wait for enough pressure and fire elecronically.
evilpenguin, Nov 06 2007

What not to do... http://www.stuff.co.nz/4266339a6009.html
.. with dry ice. These idiots got caught. [neutrinos_shadow, Nov 07 2007]

Dry Ice Bombs http://video.google...9015794510241027087
The next step in the evolution of dry ice explosives (this video) ought to be the potato gun! [quantum_flux, Nov 09 2007]

Dry Ice Potato Gun http://video.google...pe=search&plindex=2
.... and sure enough it is! [quantum_flux, Nov 09 2007]

[link]






       If the dry ice was submersied in water; would it not be wet ice? And easy to build does not imply convenient to use. Most households do not have a box of dry ice sitting on the shelf. Nevertheless; for providing weapons building instructions on the H/B and risking that black-windowed car outside your door... [+]
vincevincevince, Nov 06 2007
  

       Fire electronically? Normally you would give it a hit of gas from a lighter, a bit of hairspray or some other aerosol, stick in your spud (or orange) then press piezo to fire. What fires with co2?
the dog's breakfast, Nov 06 2007
  

       <Googling> It'd work, but there's no point in doing it--there are plenty of other propellants around, including liquid CO2, that are much easier to use.   

       Simple? You'd have to find and buy dry ice, keep it insulated, use it within a day, handle it with gloves, get it into the chamber, seal the entire hatch, carry and dispense water, wait for pressure to build up, and maintain a pressure gage. The electronic valve is workable, but still a pain. (The water isn't needed--it speeds things up a little, but it reduces useful volume.)   

       Fishbone for the word "simple".
baconbrain, Nov 06 2007
  

       [dog] Built up CO 2 pressure. Just like air pressure, held back by valve.   

       And simple, YES! For me at least. I could build a working version in about an hour, and all from items readily available in the Home Depot. Thats what I mean about simple. You don't even need to drill any holes in the PVC, wait for epoxy, just PVC-cement all the peices together and your done.   

       I will admit dry ice is scarce, but I live close to a dry ice supplier. They are 2 blocks from my house. I'm sure there are such places where you live, you just need to look.
evilpenguin, Nov 06 2007
  

       Oh, I can get dry ice--I bought some last weekend. I used it for a camping cooler, and skipped my usual trick of blowing up two-liter bottles.   

       And I could use it in a potato gun, though I'd not use water to speed the process. Although the water might keep the PVC from getting brittle from cold.   

       If you want to try making one this way, fine. I'll take off the fishbone. (I have to learn to avoid annotating before breakfast.) [ ]
baconbrain, Nov 06 2007
  

       I'm a bit indifferent to the idea, but a word of caution.   

       The vapour pressure of Co2 at room temperature is pretty bloody high, ie PVC shatteringly, horendous injuringly, you-wouldn't beleive it high. Ie 6000Kpa ish at room temperature. That's 60 atmospheres. The best DWV PVC pipe you'rer going to get will hold something like 3200psi under rediculously ideal conditions.   

       So I'd suggest one of two fixes. Best one is a PRV ie pressure releif valve set at no more than 100 psi on your chamber.   

       Second best is a ball valve and a pressure gauge. Crack the ball valve just a tiny bit, so the equilibrium pressure is reasonable, ie ~100PSI.   

       Fankly, these are both pretty piss-poor safety measures. In an industrial system, you simply can't have a component with a given failure pressure, hard-piped to a source of gas at a higher pressure, regardless of the valving in between. It's just not safe.   

       I hate to say it like this, but you're better off using the ol' hairspray - and - BBQ lighter combo. This thing will bite you someday, and it'll bite really really hard.
Custardguts, Nov 06 2007
  

       [custardguts] Your right. This would really just be a death bomb if the pressure built up. I have devised some safety precautions: 1. PSI guage 2. mechanical pressure relief valve (water heater TP valve) 3. On one of the PVC cement bonded joints securing the pressure chamber, the cement would be applied sparingly, allowing a built-in failure point. This joint would be located somewhere away from the user. 4. loud alarm triggered by over pressure situations 5. Heavy coating of triple-anitbotic smeared all over, just in case of explosive fragmentation
evilpenguin, Nov 07 2007
  

       And maybe this would be safer if built with metal (blackpipe)? Or would that just make deadlier shrapnel?
evilpenguin, Nov 07 2007
  

       Wiki dry ice bomb. This is dangerous and, in many places, illegal. I have to give a "Don't try this at home" fishbone...
dbsousa, Nov 07 2007
  

       Shrapnel would be deadlier...to answer the question. The energy stored as latent heat in phase transitions is quite remarkable and responsible for some powerful energy releases. It all depends on the volume of sublimating solid and the ambient temperatures, and that makes it unpredictable. Not suitable for competition purposes, as most competitions would require a repeatable performance. Even land speed records require more than one attempt, with both attempts higher than the existing record.
4whom, Nov 07 2007
  

       I have actually tried this before, except I used a burst disk. It worked well, but I went back to using and air compressor because I didn't like not knowing how much pressure was building up, or if I had made the burst disk to thick. It worked great for pvc water rockets though.
Tetra, Nov 07 2007
  

       This cannon could be pressurized with a fill valve and a bicycle pump. The limitations of the bike pump will help prevent dangerous pressures inside the PVC.
bungston, Nov 07 2007
  

       bicycle pump = boring   

       Dry ice = lethal   

       lethal = entertaining   

       therfore   

       dry ice = entertaining
evilpenguin, Nov 07 2007
  

       A combination of the potato gun and a "dry ice bomb" could be used to produce a cannon which fired after some delay, allowing those firing it to leave the area and avoid blame. This combination also reduces strain on the cannon and the risk of cannon failure and PVC shards. It is simpler in that there is no valve or firing mechanism necessary, thus making the cannon cheaper and easier to abandon.   

       One would make a cannon with a firing chamber containing a dry ice bomb (for example, a 2 liter soda bottle containing dry ice). When the pressure inside the bottle ruptured the bottle, it would explode and the released gases would propel the contents of the cannon outwards.   

       I could see this as most useful for a prank - for example, a delayed CO2cannon filled with Sphagettios positioned in the bushes near an outdoor party.
bungston, Nov 09 2007
  

       how about:

-liquid hydrogen instead of nitrogen etc.
-super hot water etc.
-combine the two and put through igniter
-double bam :)
xxobot, Nov 09 2007
  

       My coworker and I have a spud gun in the back of the truck for off road excursions.   

       An almost 2 inch dowel, about 2 inches long with a steel round drawer knob. The back end has pieces of cloth screwed to the back to keep it oriented.   

       For propellant we found Axe deodorant works really well with very little gunk buildup inside the chamber.   

       This setup punches the knob through 3/4 inch plywood.
Giblet, Nov 09 2007
  

       for sphagettios one might need a sabot.
bungston, Nov 09 2007
  

       The humble potato makes a potent weapon.... imagines a hopper of mashed potatoes feeding a sort of multi-barrel gun - a Vulcan Chip Cannon.
xenzag, Nov 09 2007
  

       Nice link [quantium]   

       but I think thats a dry ice bomb inside a PVC tube. Close, but thankfully not exactly my idea.
evilpenguin, Nov 10 2007
  
      
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