Show us your pneumatic spud gun! Discuss pneumatic (compressed gas) powered potato guns and related accessories. Valve types, actuation, pipe, materials, fittings, compressors, safety, gas choices, and more.
Ok i have the right kind 3/4 sprinkler valve modded to what i believe is correct. Everything works perfect, until i shoot it.
the valve opens so slowly that the pressure is greatly reduced and the projectiles might as well fall out of the barrel.
The only other problem i can think of is that i built the cannon with a stock, but the gas runs throughout the stock as well, which might be making the flow of the pressurized gases run awkwardly.
If that is the problem, how would i seal off an already glued stock?
And if not, what's wrong with my valve? ( i used the blowgun mod)
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Last edited by pbpenguin5 on Sun Feb 17, 2008 1:21 pm, edited 1 time in total.
it's not leaking at all, it's just not dumping the air all at once like a normal ball valve does on simpler cannons.
i'll post pictures as soon as i can, i usually post in school, like right now
and the stock is joined by a T fitting, one to the stock, one to the pressure chamber, and one to the barrel. I'm thinking the air is traveling into the chamber and stock, then conflicting at the T fitting to escape.
In my opinion, you either have yourself too small of a reservoir nad too big of a pilot volume that you end up venting most of your chamber before the pilot volume is exhausted enought to open the valve, but since you said the stock is part of the chamber too, you should have enough chamber volume.
Did you dissassemble the valve and clean it all out?? that might be a problem too.
Yea, that's definitely going to get you at least a tazer.
<a href="">DONT TAZE ME BRO.. DONT TAZE ME... AHHHH</a>
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The inside diameter of the path that the air has to go through must be the same or larger than the input port on the sprinkler valve. So, since you're using a 3/4" sprinkler valve everything between the valve and the air resevoir must be at least 3/4" so that it doesn't restrict the air flow.
elitesniper wrote:i think your chamber is too small
I got the idea for this of instructables.com with a guy who made a very similar sniper with a lesser size chamber that sent C02 cartridges like bullets.
my problem is the air isn't escaping simultaneously
Same problem I was having... your mod is hendering the movement of the diaphragm AND what dewey-1 said above, valve is in wrong direction...lol
On top of the valve, you seem to have the threaded 3/8" fitting tightened down to the nut, which would leave a few threads showing on the underside of the valve top. It that's the case, the extra threads are restricting the diaphragm from opening all the way. Either back the fitting out until the threads are flush with the inside of the top, file a couple of threads off of the fitting so where you can actually tighten the fitting back down tight, and/or mod the white tip in the center of the diaphragm. I filed threads off and filed down the center tip down to almost level with the actual diaphragm. Works great now.
EDIT: You will have to apply a small amount of epoxy to the top to seal off the small hole that runs through the plastic piece in the diaphragm.
Last edited by fireman565 on Tue Feb 19, 2008 2:38 pm, edited 2 times in total.
Your air chamber is designed OK and it's plenty big enough. How much air pressure are you puting into it? Also, there's a small drain hole in the exit port of the sprinkler valve. It should be right there inside the 3/4" threaded hole. Be sure that hole is plugged up with epoxy. Just a thought. Also, Make sure the sprinkler valve isn't backwards. There's arrows on it to show the direction of flow. The blow nozzle your using may have a rubber tip on it that is too small to let enough air out to allow the diaphram in the sprinkler valve to pop-up. The blow nozzle itself may be too small. You have to let a good amount of air out of the top of the sprinkler valve quickly. Also, It doesn't matter if you have a guide rod or not. I've used sprinkler valves with and without guide rods and they all work fine.
Last edited by DVLCHLD on Sun Feb 17, 2008 3:07 pm, edited 1 time in total.
i agree with fireman, you are probably blocking the movement of the diaphragm with you're blowoff. i have the identical valve on my cannon, and it works great as long as pressure is high enough, below 100 psi it doesn't seem to open as fast
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