Pnumatics (nothing to do with cars but i know some of you know)

[CBFryman]

Working on an extra credit project for physics. not that i need it (im am teh masterzzz 105 on the 1st test, was the highest and the classand the next was a 95 followed by an 80, prety much everyone else failed) and then a 110 on the retake, we are working on projectiles and motion in two dimentions.

well im taking what i learn about motion in two directions and what ive leaned about force and what i learned in chem about gas pressure and applying it all togather in pnumatic projectiles. ie air powered potato launchers.

im not down with the whole 2-3" barel since the pnumatic potato launches ive seen in person all use this size range, have an uber small air tank and cant quite match up to combustion potato launchers of the same size.

im thinking 1 1/2" barel with 3 or 3 1/2" air tank. the barel maybe 3' and the tank maybe half that. tank pressurized with CO2 or a bike pump to 100PSI or so and let 'er rip.

however my question is about valves, it seems as though your ball valve which you pick up from lowes doesnt have the release capasity or speed for such a project (looking to out launch my teachers combustion potato gun which he says can fire your averago idaho potato 250-300yds) are there any other valves which i could pick up with a better release capasity? butterfly valve would seem to be the best but i dont know if where to get one.

[public]

Check the graybar catalog. www.graybar.com
Lots of cool stuff. You may want a slide valve(like a trumpet uses), very quick action to full pressure. These were used on steam locomotives so they can take a lot of pressure.

[Moppie]

What about a rotary valve?

[CBFryman]

Originally Posted by Moppie

What about a rotary valve?

you tell me

[Moppie]

I fail to see the joke?

http://www.google.com/search?sourcei...q=rotary+valve

[CBFryman]

im looking for something cheap. manual opening. the majority of thoes look like butterfly valves with actuators on them to open them on demand.

[TheSilentChamber]

Manual valves for air suspension. They are fairly cheep, will hold the pressure and you can get some that flow a very large amount (1" ones if you could find them would be the best bet).

[Alastor187]

Have you checked this website out:

http://www.spudtech.com/detail.asp?id=39


The products are rather expensive in my opinion but it is a good resource on spud-gun technology.

[superchuckles]

if you're looking for a way to get the "instant pressure" kind of shock that i think you're wanting to get (instead of the gradual increase that even fast valves would give), perhaps you're going about it the wrong way. in the design of your gun, immediately after the air valve, but before the potato, you should put a rupture disk that will blow at approximately 90% of the total pressure you want to apply. this way, you know that you're initial pressure will never be below 90% of the total, and that the lag time from 90% to 100% is going to be negligable compared to the lag time of going from 0% to 100% without the rupture disk. the thing that i'm wondering though is, if you're going to be able to develop enough cylinder pressure. 100psi is nothing compared to the pressure created by an explosive charge of ether (starting fluid) going off in one of those. i'd estimate somewhere closer to 350 to 500 psi from one of them. anyhow, when i was in the air force, they used rupture disks on liquid oxygen storage tanks to keep them from reaching too high a pressure & exploding - but for your gun, it sounds like just the thing even though for a totally different reason. they were made of aluminum foil disks for LOX tanks, i'm sure you could do some experimenting & figure it out relatively easily.