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Newbie questions

A place to ask general spud cannon related questions.
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Newbie questions

Unread postAuthor: MrPotatoHead » Tue Jul 18, 2006 12:04 pm

Just got interested in this potato madness and have a couple of questions.

Which tends to deliver more energy, pneumatic powered or fuel powered? I have heard that the pneumatic powered does but that seems hard to believe.

Secondly was thinking of building a pneumatic with a piston. I have seen many piston guns that then used sprinkler valves with the modified top so you can attach the air tool to it. Why not just attach air tool to the back side of the piston? Won't the air behind the piston release fast enough with just an air tool or do you really need a sprinkler valve there?

Thanks in advance.
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Unread postAuthor: Darkerweb12 » Tue Jul 18, 2006 12:14 pm

Combustion spudguns harness the stored energy in the propellents of areosol sprays, these propellents are often , butane, hexane, and sometimes alcohol. When you egnite the areosolized fuel, it combusts, breaking down the long chemical chains, and producing hot gas that takes up much more volume than the fuel originally did, producing pressure that pushes the potato out.

Pneumatic spudguns harness the stored energy of compressed gasses, most commonly air, but some higher end guns use helium. When you compress air, it is like coiling a giant spring, and the harder you compress this air, the harder it pushes back. They harness the energy by releasing this air all at once, and that force gets put upon the projectile.

Comparativly, Pneumatics are much safer, quieter, and predictable. And they can be more powerful than combustions.

The sound you get when fireing a pneumatic spudgun is like a big SWSHHHH, or depending on your valve setup, a loud honk. When you fire a combustion spudgun, there is no valves to augment the sound, and it has a large BOOM and sometimes a muzzle flash.

It's mostly just a personal preference, but I reccomend you to build a combustion first, then a pneumatic, as they are a little bit more complicated.
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Unread postAuthor: Shrimphead » Tue Jul 18, 2006 12:20 pm

Actually... pneumatics really aren't safer. They are just generally thought to be because there is no combustion involved. They really could be considered more dangerous because they are normally used at pressures of around 100 psi, where combustion guns only create up to 60 psi. But if built safely, neither are really dangerous. And to answer your piston question, the reason sprinkler valves are used to actuate the piston rather than blowguns is because they have more flow and so the air is released quicker. This causes the piston to actuate quicker which shoots the projectile farther.

I would suggest to make a ball valve or a sprinkler valve pneumatic before you try a piston. Pistons can be really hard to get to work right.
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Unread postAuthor: MrPotatoHead » Tue Jul 18, 2006 2:19 pm

I was thinking of buring the breach portion of the barrel into the chamber portion and was thinking of putting the sprinkler valve inside the chamber and running the brass fitting that gets added to top of valve out through the side of the chamber and sealing the brass fitting at the chamber wall, so it won't leak.

This would theoretically work ......... right?
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Unread postAuthor: Shrimphead » Tue Jul 18, 2006 2:50 pm

There are a few problems that I see with that idea. You would need a large chamber (probably 4", but maybe less without the solenoid). Also I don't know if the sprinkler vavle can handle all of that pressure pushing on it from the outside. It would be cool if it worked though, because it would be a non-piston or diaphragm coaxial.
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Unread postAuthor: PVC Arsenal 17 » Tue Jul 18, 2006 2:59 pm

So you're saying it's like a coaxial but the sprinkler valve replaces the piston? hmmm...

Like this?? Image


If that's what your thinking, then it would be possible but extremely difficult to do without pipe taps and what not. It wouldn't be nearly as powerful as a regular piston/diaphragm though.

It's an interesting idea...
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Unread postAuthor: Darkerweb12 » Tue Jul 18, 2006 4:02 pm

If that is what you are thinking, that is a really cool idea, I don't think anybody has thought of that before...
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Unread postAuthor: trae08 » Tue Jul 18, 2006 4:10 pm

Actually i just thought this up the other night but my idea was to run a short hose from the modded sprinkler valve to the inside of the chamber. Then a hose from that same spot on the outside to a blower. if that makes sence. but ive only started building it. My lack of funds has post poned construction.

Its a little sloppy but heres the basic design.

Cant really see it all that great but the red is the hose theres 2 seperat hoses one threads into the inside of the tank and one threads onto the outside meetig the one on the inside the black thing in the front is the gauge the thing in the back is safty popoff. when i get it finished it will be powered by co2 an i was thinking of a design revolving around one word "portability"

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Unread postAuthor: Mihlrad » Tue Jul 18, 2006 4:27 pm

isnt the entire point of a piston valve that it gets more flow then a sprinkler... if you do this then you get the same flow you get from a sprinkler valve wouldnt you? Correct me if im wrong.
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Unread postAuthor: trae08 » Tue Jul 18, 2006 4:37 pm

u would but its just a cool design and its more portable sprinkler valve this way. plus i dont know how to make a piston an i dont really want to but im sure i will one day until then this is my alternative
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Unread postAuthor: MrPotatoHead » Tue Jul 18, 2006 9:27 pm

Originally was thinking something like this. This would include the piston. But seeing as this would be my first build maybe I should leave out the piston or just dive right in and go balls out :lol: .

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Last edited by MrPotatoHead on Tue Jul 18, 2006 9:43 pm, edited 1 time in total.

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Unread postAuthor: trae08 » Tue Jul 18, 2006 9:41 pm

where does the other end of that sprinkler valve go?
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Unread postAuthor: MrPotatoHead » Tue Jul 18, 2006 9:56 pm

trae08 wrote:where does the other end of that sprinkler valve go?


One end has the piston attached and the other end goes to the outside to allow air from piston to escape.

The air tool (connected via the red hose) only allows the air in the sprinkler valve to escape (air trapped between the top of sprinkler valve and the diaphram) which accuates the sprinkler valve allowing the air trapped behind piston to escape rapidly. That air trapped behind the piston needs to go to a low pressure area (outside the pressurized chamber).
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Unread postAuthor: trae08 » Tue Jul 18, 2006 10:03 pm

oh i dont really kno how piston valves works thats why i like sprinkler but i guess it makes sence
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Unread postAuthor: MrPotatoHead » Tue Jul 18, 2006 10:48 pm

trae08 wrote:oh i dont really kno how piston valves works thats why i like sprinkler but i guess it makes sence


In a sense the piston valve has a faster reaction time and larger volume area allowing more air to rush past it as opposed to the sprinkler valve.

You want to maximize all of the air pressure inside the pressurized chamber before your projectile leaves the end of the barrel. It may be a difference of having 1/2 the usable air pressure make it through the valve as opposed to having almost all usable air pressure make it through the valve.

You can put more air pressure into the expansion chamber but eventually the pvc will fail, so once max pressure is realized then the next step is to make the inner workings (valves and what not) more efficient to increase projectile velocity.

Someone correct me if i'm off, as I am still a newbie.
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