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how do you make a piston valve?

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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how do you make a piston valve?

Unread postAuthor: THEMOST » Sun Nov 05, 2006 6:06 pm

how do you do it ? i cant understand any of the diagrams they briefly explain. But what I mostly dont understand is how you open the valve. Could someone please tell me how they work.

(yes I have googled it and I've spent about 30 min)
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Unread postAuthor: Infernal2 » Sun Nov 05, 2006 6:19 pm

Perhaps you should turn your attention to the HOW-TO button at the top of your page?
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Unread postAuthor: THEMOST » Sun Nov 05, 2006 6:22 pm

Ive done that and there wasnt anything on piston valves!
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Unread postAuthor: kyle1292 » Sun Nov 05, 2006 6:25 pm

check out my piston thread its Kyle1292 piston questions, theres a link in there
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Unread postAuthor: kyle1292 » Sun Nov 05, 2006 6:27 pm

KYLE1292 Piston thread*
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Unread postAuthor: kyle1292 » Sun Nov 05, 2006 6:27 pm

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Unread postAuthor: THEMOST » Sun Nov 05, 2006 6:31 pm

Yeah I was just reading that what are the odds. I get it now. That was a really good way to explain it on that site by PCguy.
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Last edited by THEMOST on Sun Nov 05, 2006 6:32 pm, edited 1 time in total.
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Unread postAuthor: SpudStuff » Sun Nov 05, 2006 6:32 pm

Wow that is like a record! Use the freakin edit button!

Link
Stop Complaining and use the search button!

Video Tutorial:

Long link
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Unread postAuthor: MrCrowley » Sun Nov 05, 2006 9:59 pm

just remember next time no need to start a whole new thread when theres been four in the last few days and theres a piston animation floating around here i would give it too you but i lost the link just search it on these or the spudtech forums.
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Unread postAuthor: POS » Mon Nov 06, 2006 5:16 pm

Someone asked me once by PM how the valve works, now here's my answer :

With a 2" T you can only use a barrel with a ID of 1.5 ". The barrel always needs to be smaller than the piston diameter, due to the airpressure.

The piston is pushed against the barrel, cause the pressure in the barrel, and so, in mid air, is zero. The pressure in the chamber, and around the barrel in the T is the pressure you work with, lets say 100 psi (7bar).

So the piston is pushed to the barrel with a pressure of 100 psi. Behind the piston is the pilot chamber. There the pressure is also 100 psi. When you empty this pilot chamber, trough the pilot valve, (which is mostly a blowgun, but bether, a sprinklervalve. (I use a ball 3/4" valve for that)) the pressure behind the piston drops to zero. The piston should seal enough to prevent the pressurised air in the chamber to enter the pilot chamber and exit trough the pilot valve. Tight seal isn't nessesary. The piston must be able to move freely.

So anyway, the pressure behind the piston drops to zero, and the pressure in the barrel is also zero. Due to the fact that the barrel diameter is smaler than the diameter of the piston, and the piston chamber, the power from the pressurizes air in the chamber works harder on the piston, moving it in the direction of the pilot valve, than it works the piston pressed against the barrel.
You could say that behind the piston the chamber is bigger than the barrel, so the chamber, which is at a lower pressure than the main chamber, sucks harder on the piston than the barrel does.
The result of this is that the piston will move backwards toward the pilot chamber, releasing the barrel, so the pressurized air from the chamber can ascape trough the barrel, pushing out your ammo.

I hope you understand the working of the valve now. You should be able to figure out how it works and how you can make one.

To seal of the piston in the piston chamber (pilot chamber) I use ducktape, raped around the piston, until it seals enough, but stil can move enough.


Hope you get it now ...
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Unread postAuthor: POS » Mon Nov 06, 2006 5:20 pm

Oh, and for the other guys, when someone ask for something, is it that hard to give him a propper answer, instead of yelling and telling him to look elsewhere. Just help the guy out. Forgotten your first steps in spudding ? I sure din't forget mine. Just help the guy or shut up. No one needs useless comments. Some of uss read a lot here, and if we have to open every topic to only read crap, it isn't fun anymore. Don't post to just post something and get spudbux. It's lame.
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Unread postAuthor: Scope » Tue Nov 21, 2006 9:09 pm

Ok I know that this thread is kinda sorta dead, but i have a legit question. I plan on building the valve that spudstuff posted(thanks). After reading POS's post i have been left wondering. Do you put a schrader (w.e u use 2 fill) in to your pilot chamber and your holding chamber (main chamber). Do you fill the two seperatly?? Does the pilot chamber have to have a higher pressure then the main chamber?

Thank you to anyone who answers.
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Unread postAuthor: SpudStuff » Tue Nov 21, 2006 9:16 pm

Yes the fill should be behind the piston. That pushes it foward to seal.
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Unread postAuthor: Scope » Tue Nov 21, 2006 9:20 pm

Is there two fills?
One for the chamber and one for the piston?
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Unread postAuthor: SpudStuff » Tue Nov 21, 2006 9:22 pm

No one fill from behind the piston. It leaks past and fills the chamber.
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