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select fire auto-piston design

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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select fire auto-piston design

Unread postAuthor: iknowmy3tables » Wed Mar 24, 2010 6:58 pm

so auto pistons are nice, but I was thinking what if the piston could also be used as a trigger valve. if the pressure input was regulated to just below the opening pressure this design should work.
but first I have to ask do regulators lose substantial amounts of flow when the pressure on the output side of the regulator is near the pressure setting? would this effect prevent the design from having high ROF? if so how could it be fixed?
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Unread postAuthor: ramses » Thu Mar 25, 2010 4:23 pm

That looks good. I would use it as a pilot valve, depending on your caliber, to keep the spring force/trigger weight manageable.

Regulators do drop off in flow as pressure reaches what they are set for, so you will have some "shoot down" depending on your regulator, volume of the buffer chamber, bore, etc.
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Unread postAuthor: Hawkeye » Thu Mar 25, 2010 6:02 pm

Air leakage at the trigger rod?
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Unread postAuthor: ramses » Thu Mar 25, 2010 7:25 pm

probably negligible.
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Unread postAuthor: velocity3x » Thu Mar 25, 2010 7:26 pm

I just don't get it. I can see that pulling either trigger will fire the gun but, what is going to reseat the piston after the "Auto Trigger" is pulled and the chamber evacuates? Without releasing the auto trigger after each shot, the piston will remain unseated. If the trigger must be released after each shot....it's not an "Auto trigger". The "Auto Trigger" seems to be nothing more than the "Semi trigger" with more leverage and longer throw.
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Unread postAuthor: jackssmirkingrevenge » Thu Mar 25, 2010 10:29 pm

I think it's a bit of an unnecessary complication, with an autopiston design like this one light pressure on the trigger (assuming it's spring loaded to return shut unlike the ball valve setup illustrated) is enough to give you one shot.
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Unread postAuthor: iknowmy3tables » Fri Mar 26, 2010 12:23 pm

velocity3x wrote:I just don't get it. I can see that pulling either trigger will fire the gun but, what is going to reseat the piston after the "Auto Trigger" is pulled and the chamber evacuates? Without releasing the auto trigger after each shot, the piston will remain unseated. If the trigger must be released after each shot....it's not an "Auto trigger". The "Auto Trigger" seems to be nothing more than the "Semi trigger" with more leverage and longer throw.


that's because you have to understand auto pistons first, the concept behind an auto piston (also known as snap valves or pop-off valves) is that when the pressure reaches the opening point it opens but once it's opened there is a larger cross sectional area of the piston revealed, more area means more force to open the piston, so the piston flys open and stays open until there is a substantial pressure drop

@JSR
yeah but I kinda need semi auto ability for a nerf gun because the rules for HvZ games on my campus, also typical blow guns have bad flow for filling larger chambers for semi and full auto purposes, unless you'd prefer something like a regulator bypass valve setup

so guys I'm considering this for a nerf gun, I'm thinking of using a piston 1" to 1.25" in diameter and a chamber fairly small like a section of 1" pipe less then an foot long, and for an air source nothing special just a typical air compressor regulator. so any guesstimations on performance and feasibility?

also I don't have any concern for leaks around the rod, as you should know any spot that isn't constantly under pressure doesn't need to be air tight, which is why almost no one uses o-rings on their breech setups
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