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Not gun connected pistons

Post about things you have launched or thought about launching. Also post about various materials used for building cannons. No posts about explosive projectiles!
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Not gun connected pistons

Unread postAuthor: john bunsenburner » Fri Nov 07, 2008 5:54 pm

Ok the name says it all; i want to build a gun whaere i have a back pack with an air reserve. the thing is i whant the gun to look real so i came up with the following:

I will have my chamber in my backpack, there i will have a piston that is barrel sealing but instead of a barrel i will just use a piece of copper tube. At the end of that i will have a HP air tube/hose. This will lead to the gun. The question of how to fire is solved by having the exaust valve also connected by a tube to the gun and the ball valve used as my exaust will be opened by a spring pwered mechanism.

Who here has ideas, or comments. Is this idea just plain mad or does it have potentual(sorry about all spelling i just got back from a 4 hour disco and a 3 hour dinner).
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Unread postAuthor: TurboSuper » Fri Nov 07, 2008 7:14 pm

It will work. A while back Sgort built a backpack based combustion launcher, and it worked real well. The only downside is the dead-space created by the air hose, but it shouldn't adversely affect performance too much.
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Unread postAuthor: john bunsenburner » Sat Nov 08, 2008 4:19 am

cool, i have to try that(hmm i had an old school bag somewhere here...)
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Unread postAuthor: starman » Sat Nov 08, 2008 10:58 am

Sounds pretty inefficient, with the flex barrel "extension" and pilot "extension", you'll have lots of dead space on both sides of the piston.
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Unread postAuthor: john bunsenburner » Sat Nov 08, 2008 12:35 pm

What if i pressurize the whole system before use and then have one valve to set it all off?
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Unread postAuthor: starman » Sat Nov 08, 2008 2:54 pm

Then you're back to having a valve of some sort back on the gun....the piston in your backpack would then be useless.
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Unread postAuthor: john bunsenburner » Sat Nov 08, 2008 4:48 pm

Well i have an exaust valve anyhow, if the system is presureized then it doesnt matter if it is next to the piston or 10km away...
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Unread postAuthor: TurboSuper » Sat Nov 08, 2008 5:12 pm

Well the system is only going to be as powerful as it's fastest valve. If you already have an exhaust valve, why have a piston valve?
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Unread postAuthor: john bunsenburner » Sat Nov 08, 2008 5:15 pm

A piston valve system always has an exaust...Have you ever acctually looked into piton valves?!
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Unread postAuthor: starman » Sat Nov 08, 2008 5:28 pm

john bunsenburner wrote:Well i have an exaust valve anyhow, if the system is presureized then it doesnt matter if it is next to the piston or 10km away...


I assumed you were talking about pre-pressurizing the flex "barrel" too??

It does matter about the length of your pilot. It's considered pilot dead space and adversely affects performance...certainly an 10 km one would be a non-starter.
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Unread postAuthor: john bunsenburner » Sat Nov 08, 2008 5:40 pm

If the pilot, any everything else is pressurized so that i just open one valve(ball valve) and the air comes out(pilot and the air in the chamber) to push the projectile out of the barrel then the performance and efficency are not effected are they? Tell me if i am wrong but i think im right(lol...)
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Unread postAuthor: TurboSuper » Sat Nov 08, 2008 5:43 pm

john bunsenburner wrote:A piston valve system always has an exaust...Have you ever acctually looked into piton valves?!


Oh, you mean the pilot exhaust?


Look, any barrel space you have that isn't blocked by the projectile in question is going to reduce effeciency. It's a fact of life. If you're willing to live with that, then go for it. Unless of course you want to fire through the air hose somehow...
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Unread postAuthor: john bunsenburner » Sat Nov 08, 2008 5:51 pm

But does a big chamber reduce efficency compared to a small chamber of the same pressure? no. if i have the whole hose at the pressure i am using then its like having one big chamber in hose form...
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Unread postAuthor: TurboSuper » Sat Nov 08, 2008 5:56 pm

You said in your original post that you wanted a piston valve connected to an air reserve inside a backpack. Now you're describing a piston valve connected to the actual gun and only the air reserve inside your backpack.

Make up your mind, plzkthx.
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Unread postAuthor: john bunsenburner » Sat Nov 08, 2008 6:03 pm

the piston and air reserve go together...but yes everythings in my back pack
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