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Thought I'd share my first ever attempt at any sort of cannon. I got the idea from dry ice devices, thinking that it'd be a pretty good way of generating pressure for projectile. So here's my setup. About 1.5m of 40mm uPVC Gas Pipe (rated to 2100kPa), sealed at one end with an end cap and the other with a 25mm Ball Valve (rated for 2000kPa). I fill the tube with about a litre of hot water from the tap, then crush up 50g-75g of dry ice into as fine powder as i can get (dry ice is $7.50 AU / kg). Quickly chuck the dry ice in the open ball valve, then seal it and wait about a minute. I've got a barell that screws onto the other side of the ball valve; perfect for shooting eggs and ping pong balls. Put the projectile in, open the ball valve and bang. Applied a bit of physics and I estimate the muzzle velocity is about 25-30m/s.
I know its basic, but for less than $50 AU, and a cost of about $0.50 per shot for dry ice, i reckon its a pretty simple and straightforward way to shoot things.
Wouldn't mind a bit of advice though:
Do you think it would be safe to put more dry ice in (i.e. increase the pressure). As the pressure goes up I am dissolving a fair bit of Carbon Dioxide into the water and hence losing pressure, and i don't have a gauge so I can't estimate or measure the pressure. I'm worried about the pipe failing.
Edit by jrrdw
You may run into some trouble with the (dry ice) and moderators here. Dry ice bombs are strictly prohibited, but I'm unsure if this falls into that category.
And no, it isn't safe! While 2000kpa sounds like a lot, it isn't. No where near enough for carbon dioxide (unless regged). Dry ice will also make the cannon VERY brittle so take caution. A pop off valve and a gauge would be a good investment.
Lecture aside, nice cannon, good ingenuity and welcome to spudfiles! If you want to use more pressure you could use a rupture mechanism (burst disk) or a stronger pipe.
Edit: good pictures btw!
Is this the 1st working dry ice cannon on Spudfiles??? I beleave so. I would follow inonickname's safty advise it is sound and good info!
I send you a PM about the other.
Welcome to Spudfiles.
When life gives you lemons...throw them back they suck!
Uh oh. Death cannon.
1- Dry ice can create pressures of more then 800 psi. Your pipe is rated to 300 psi.
2- You dont have a gauge, so how are you going to know if you are about to get injured or not?
3- Ice is cold. When PVC pipe is that cold, it becomes VERY brittle. One shock or drop and it shatters in pieces, which, fly away in all directions since there is pressure inside. Most people call this an explosion.
Never use PVC cannons in the snow, and even worse, in combination with dry ice.
Welcome to spudfiles, but I want your next cannon to be filled with air OR made out of steel!
Till the day I'm dieing, I'll keep them spuddies flying, 'cause I can!
Spudfiles steam group, join!
lol you use kpa... I am not against it but it would be a good idea to switch to psi or bar&atm... it would make your post easier to understand...
Children are the future
unless we stop them now
Yeh, while it hardly matters bars and psi/pounds in^2 are the most widely accepted, most people here know them. By the way, 1 psi is 6.9 (or 7..) kpa. A standard operating pressure of many standard pvc cannons is 100, give or take ten psi.
Dry ice probably wont reach it's full potential (I'd be willing to guess the ratios aren't perfect) but the pressures and temperatures are unsafe in pvc. Copper, iron, steel, galvanized, titanium, carbides, flux capacitors and brass are good construction materials for such things.
If it's impossible to talk you out of the pvc (hope not) then at the least use a pop off/safety valve and guage, or even better a reliable burst disk.
Lets see what you can turn out in the future, it's a good idea to pay heed to comments here but don't get too down on it. People here will pick and examine every safety aspect, but they have good intentions. Mainly, your livelihood and the future of the hobby.
On topic: Eh Eh Ehhhh
This was my concern when i started out. I'm aware of the pressures that dry ice can produce and the temperature issues, but I think I've found ways around those problems:
For the pressure, I've applied a bit of high school chemistry (I'm in final year atm), and worked out the pressure I will get based upon ideal gas law. After that, I leave a bit of margin for error to ensure im well under 2000kPa. Problem is, i think a lot of my CO2 is dissolving into the water like in soft drink (due to the pressure), so what I really need is someone with a strong chemical background who can tell me the solubility of CO2 in water at 2000kPa and 60C (about 150F).
As for the brittleness of PVC, i fill the pipe with the hot water first, and crush the dry ice up. This way, the temperature difference results in very quick sublimation so as to avoid cooling the actual pipe down and making it brittle, whilst still giving me time to seal the pipe.
As for a gauge or burst valve, I'm trying to keep costs low, so anyone got any ideas as to where i can get a cheap gauge in Australia? Store i bought the stuff from wanted to charge me $120 AU for one so I passed.
And I can't see how I'm the first one to do this. It seems so simple and obvious.
@Ducky: Welcome to Spudfiles. I would advise dropping the whole dry ice cannon in PVC concept. They are unpredictable and pack a huge and dangerous punch.
does anyone use kilopascals as a measurement anymore?
Bar, PSI, lets try to keep it to those two atleast lol.
well yes, but 1 bar = 100kPa, next you are gonna measure something in barye or dyne.
I'm just giving you a hard time.
Bar and kilopascals are fine.
While PVC becomes more brittle a lower temperatures, it also increases it pressure rating. Hot PVC can handle a LOT less pressure than cold. Brittle just means if you drop it (and in doing so exceed the stress limit) it might explode.
At 60*C the rating of PVC pipe falls to just 22% of its stated rating, so your gun is rated to only 4 bar when you put in the hot water! PVC has the worst temperature-rating decline of all pipe plastics, I think it might be wise to retire this until you can at least get a gauge and thermometer installed.
Failing that, just change your chamber pipe. MDPE or HDPE pipe has a higher rating, and a preferrable failure mechanism, so if you can get hold of some, use that. Even better, use metal!
Those who would give up Essential Liberty to purchase a little Temporary Safety, deserve neither Liberty nor Safety. -Benjamin Franklin
I'm going to go back on my advise of a gauge. You don't need it, IF you do something like this:
1. Go to hardware store and buy a union. It's basically a coupling that threads together with an o ring to seal it. Replace the ball valve with this.
2. Get a tire inflater (compressor attachment) and use layers of material as a burst disk; aluminum foil works.
3. Use the gauge on the inflater to check what pressures they fail at, removing or adding material as necessary.
4. When ideal pressure (bursting) is reached factor in a safety margin and the slight amount of time the pressure will build up in the barrel, and you're set!
Very reliable, just make sure you test before using them! I don't see any good outcome if you don't.
And yes, I do believe flux capacitors are a viable method of powering spudguns.
I certainly do. I do a lot of my spudding maths in Pascals, and kPa comes into that automatically at times.
If you get into really serious engineering maths, then kPa is far more likely than using Bar, which are not an SI unit - they're not part of the SI prefixes, being 10<sup>5</sup> Pa.
There's times when I have to work in Atmospheres, and sometimes I become unfortunate enough to have to use something archaic like Torr, because I need some data and when I find it, some little cock supplied it in bloody stupid units.
Of course, my working generally gets translated into more familiar units for the forum.
Does that thing kinda look like a big cat to you?
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