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Piston

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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Unread postAuthor: elitesniper » Tue Jan 01, 2008 5:40 pm

Hey guy i need to ask you a quick question about pistons well, um for pistions do the need and oring ? do they have to be air tight in the tee were you acutate and relese the pressure or can they have just a little tiny room left but they can still seal by you blowing into it
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Unread postAuthor: MrCrowley » Tue Jan 01, 2008 5:44 pm

No they don't need an oring.

If they have an o-ring they need a equalisation hole where the air from behind the piston can get through into the chamber.

As long as the piston is lubed up and a good fit in the pipe it should be fine. At first it may seem that air wont seep through, but it will as long as you can move the piston with your finger.

<A HREF="http://www.spudfiles.com/forums/how-to-make-a-pneumatic-cannon-with-a-2-piston-valve-t10381.html">This Might Help</a>

Oh and I can't seal my piston with blowing, but it does seal at under 5psi from the compressor when lubed up well.
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Unread postAuthor: elitesniper » Tue Jan 01, 2008 5:54 pm

Oh right thanks MrCrowley again, your always so much help :D does this look like a good piston? its hollow though but its made of really hard aluminum
Image
Image
Image

the pistion is supposed to seal like that agianst the barrel right? and the back has nothing thats ok right yea ill have a bumper
[/img]
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Unread postAuthor: MrCrowley » Tue Jan 01, 2008 5:59 pm

It's quite long, which is good and bad, more weight but takes up pilot volume. Since it's aluminium it doesn't really matter.

Yeah that's how it seals.

You may want to fill the piston with expanding foam so you don't add to the pilot volume. Make sure to keep the piston in pipe when filling it up so the foam doesn't deform the piston.
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Unread postAuthor: elitesniper » Tue Jan 01, 2008 6:00 pm

fill it full with foam or half? wait i put real packaging foam inside the pistion since i dont wana buy the expanding foam then i melted some glue sticks in it that will work well right?
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Unread postAuthor: MrCrowley » Tue Jan 01, 2008 6:06 pm

Full, may as well. It wont add weight worth noticing.

Just add small amounts at a time, it expands alot and you don't want to deform the piston.
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Unread postAuthor: elitesniper » Tue Jan 01, 2008 6:09 pm

alright thanks i hope this pistion is guna work i cant wait to try it out :D home depot is closed to day though :( how does it feel when you first try youy homemade pistion and it works really well huh huh ? :lol:
o yeah and one more thing do you think i can acutate it with a blowgun?
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Unread postAuthor: MrCrowley » Tue Jan 01, 2008 6:25 pm

Best feeling, even my dad was 'over the moon'.

Not sure what size it is, but I don't think so it looks a bit too big for a blow gun.

Really anything over 25mm(1") you want a ball valve to actuate it with.

Anything 40mm(1.5") or over you want at least a 1/2" ball valve as the pilot valve.

And anything over 50mm(2") a sprinkler valve would be best but a 1/2" ball valve works fine.

You may get it to work with a blow gun, like I did, but it will have poor performance.
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Unread postAuthor: elitesniper » Tue Jan 01, 2008 6:31 pm

but the blowgun is modded so will it work? um the tee is 1 1/2 inches i also need a 1/4 ball valve behind the quick disconnect stud right?
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Unread postAuthor: MrCrowley » Tue Jan 01, 2008 6:34 pm

elitesniper wrote:but the blowgun is modded so will it work? um the tee is 1 1/2 inches i also need a 1/4 ball valve behind the quick disconnect stud right?


Yes, but you will have poor performance.

And yeah the male end needs a 1/4" ball valve, but the female QC has a valve in it and doesn't.
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Unread postAuthor: elitesniper » Tue Jan 01, 2008 6:40 pm

but then if a put a qc on my gun i will still need a ball valve for the midde of the two studs or else when i disconnect it the pistion will acutate am i correct? :lol:
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Unread postAuthor: MrCrowley » Tue Jan 01, 2008 7:14 pm

Studs?

If you have the male QC on the gun, just put a ball valve behind it like I did with mine.
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Unread postAuthor: elitesniper » Tue Jan 01, 2008 7:23 pm

yea thats what ima do
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