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check valve effect in a piston valve using a rubber cap

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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check valve effect in a piston valve using a rubber cap

Unread postAuthor: iknowmy3tables » Wed Apr 07, 2010 3:01 pm

so I recently I've been experimenting with a secretstrike nerf gun and I learned a good bit about it's design, you can find some diagrams here

anyways one of the features is that it uses a piston valve, and for a piston it uses a sort of rubber cap in a way that creates a check valve effect that allows air from the pilot to enter the chamber, but prevents air from the chamber from entering the pilot.

so I think this could be applied to a homemade piston valve, you could make a piston out of a rubber end cap like one of these
Image
they're lighter and softer then a wood or pvc piston so you'd hardly need a bumper.

What do you guys think?
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Attachments
rubber cap piston valve.PNG
rubber cap piston valve.PNG (14.3 KiB) Viewed 524 times
rubber cap piston check valve effect.PNG
this roughly how the check valve effect works
rubber cap piston check valve effect.PNG (16.28 KiB) Viewed 524 times

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Unread postAuthor: deathbyDWV » Wed Apr 07, 2010 3:10 pm

I don't see why it wouldn't work except for the piston being too soft and bending on the way back... So it'd need to be lubricated some...
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Last edited by deathbyDWV on Wed Apr 07, 2010 3:12 pm, edited 1 time in total.
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Unread postAuthor: Hubb » Wed Apr 07, 2010 3:11 pm

I think it's worth a shot. The only negative I can see right off hand would be the friction of the piston to the pilot pipe.
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Unread postAuthor: MRR » Wed Apr 07, 2010 3:15 pm

The only problem I see is that friction increases dramatically with higher pressure. The valve could become slow or doesn't even fire at all.


edit: hubb beat me at that one
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Unread postAuthor: Gun Freak » Wed Apr 07, 2010 3:35 pm

I might try this on my new piston valve. Seems logical...
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Unread postAuthor: iknowmy3tables » Wed Apr 07, 2010 4:42 pm

here's an thought, could the static friction perhaps delay the opening of the valve so the pilot pressure would be lower before the valve opened?
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Unread postAuthor: Gun Freak » Wed Apr 07, 2010 4:46 pm

iknowmy3tables wrote:here's an thought,


The word "thought" begins with a T, which is not a vowel, therefore you would not use "an", but instead "a". :D Just messin with you. :lol:

iknowmy3tables wrote:could the static friction perhaps delay the opening of the valve so the pilot pressure would be lower before the valve opened?

Resulting in a quicker opening time? I don't think it would be much of a difference, but it sounds like it might work.
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Unread postAuthor: Hubb » Thu Apr 08, 2010 7:37 am

I would think that with the increase in friction, the piston will begin to move when the pilot is exhausted, but it will move really slow. I don't think it would work like you think it would.

I think if we could get past the friction issue, that this would be a very nice piston valve. It would have a light weight, low profile, fast opening times,...all the things that a good quality piston valve should have.

With that said, maybe if we could place a ring of pipe inside the walls of the piston to cut the friction. This would still give it the check valve quality, but also be able to be lubed up, which should eliminate a whole lot of friction.

Really, though, the only way to see if this works or not is to try it. I've been wanting to make another piston valve so I might give this one a go when I get a little bit more scratch (probably next Friday).
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Unread postAuthor: c11man » Thu Apr 08, 2010 10:36 am

i see the center of the cap bending into the barrel but it shouldnt matter because its all one peice
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Unread postAuthor: iknowmy3tables » Thu Apr 08, 2010 11:17 am

i believe it's worth a shot cause if it doesn't work well then you can just replace it with a piston made from a pvc end cap
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Unread postAuthor: clemsonguy1125 » Thu Apr 08, 2010 11:34 am

It may work but under enough pressure the center would balloon out and possibly "pop" but at say 80 psi it should be fine
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Unread postAuthor: Gun Freak » Thu Apr 08, 2010 3:52 pm

clemsonguy1125 wrote:It may work but under enough pressure the center would balloon out and possibly "pop" but at say 80 psi it should be fine


You can probably reinforce it with some washers inside of the cap or something. I think with some practice this idea could be the new piston valve technology :)
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Unread postAuthor: clemsonguy1125 » Thu Apr 08, 2010 4:44 pm

I agree but maybe a coat of epoxy would work better
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Unread postAuthor: c11man » Thu Apr 08, 2010 5:18 pm

i think washers would be better
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Unread postAuthor: clemsonguy1125 » Thu Apr 08, 2010 5:56 pm

well washers would need to be bolted on which would add more weight than just dumping in some epoxy
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