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Posted: Fri Jul 18, 2008 8:25 pm
by MrCrowley
Remember if you can find a suitable chamber with a large volume, that can be used instead of standard plumbing materials.
Such large volume chambers may include:
Fire extinguishers
CO2 tanks (for welding)
Helium tanks
Paintball tanks
Acetylene tanks
Nitrogen tanks
Air compressor tanks
I'm sure if you got your hands on one of those we could help you use it in a pneumatic spudgun setup.
The advantage is they are usually rated to a few thousand PSI or have a burst pressure over 1800 PSI. They can also be found for little or no money if you look in the right places. Downsides are weight, size and maybe thread size (might have to get welded).
Posted: Fri Jul 18, 2008 8:51 pm
by Hydra
Im 13 and look what I built..
http://www.instructables.com/id/A-15mm- ... Sniper-Ri/
Its not that hard if your 14, just read around.
Posted: Sat Jul 19, 2008 4:44 am
by MaxuS the 2nd
Yes...But PVC csts more in the Uk than it does in America. It's also harder to find. Ever wondered why so many metal cannons come from the Uk?
Also if you were to turn your sprinkler valve downwards, you would cut down on pilot volume and your scope wouldn't have an obstacle infront of it.
Posted: Sat Jul 19, 2008 6:59 am
by Ragnarok
DYI wrote:And propane combustion doesn't produce thousands of psi if it starts at atmospheric pressure... Just figure out how hot it gets, and you can get a rough idea of the pressure, because as both reactants and both products are gases, there's no overall volume change.
There is actually an overall change in the molar quantity of gases in a combustion - after combustion, there are roughly 10% as many moles of gas. Although that might sound wrong, because propane is such a dense gas, and when burnt it splits into much less dense gases, then it's actually perfectly possible for that to happen.
As a the volume of a mole of gas at any given pressure and temperature is a constant, there is an overall volume change when the gas has cooled to normal temperatures.
Posted: Sat Jul 19, 2008 10:55 am
by DYI
There is actually an overall change in the molar quantity of gases in a combustion - after combustion, there are roughly 10% as many moles of gas. Although that might sound wrong, because propane is such a dense gas, and when burnt it splits into much less dense gases, then it's actually perfectly possible for that to happen.
As a the volume of a mole of gas at any given pressure and temperature is a constant, there is an overall volume change when the gas has cooled to normal temperatures.
Thanks for clearing that up Rag. I suppose I had never really thought very much about it... In propane combustion, there would be a 6:7 ratio of volume before combustion : volume after combustion. Now we just need to figure out long term storage of O<sub>3</sub>, and we're set
Posted: Sat Jul 19, 2008 2:02 pm
by Biopyro
A perfect air chamber is a 2l drinks bottle. They can be epoxied onto 22mm copper perfectly and are ideal for a lower power ball valve gun.
Pneumatics are much better for starter guns, and with nothing to really compare it to a ball valve will be absolutely fine. Best to start with something fairly small and work up. A Ball valve tennis ball cannon will probably cost you about £70 and might be a bit of a wasted potential. Best to go for copper for now.
Whereabouts in the UK are you?