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blow forward pop-off 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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blow forward pop-off valve

Unread postAuthor: LeMaudit » Thu Nov 17, 2011 8:05 am

Hi guys,

Here's some fun experiment I'm doing with JSR's help, who's explaining me *so patiently* pressure valves basics and pop-off physics :-D

This full-auto pop-off valve have variable ROF regulated by the air flow, and have the particularity of venting the pilot volume forward. The video shows it working at 90psi. It's much louder than the poor camera sound recording ;-)

We're not convinced venting the pilot volume inside the barrel is a good idea... I just wanted to try it :-P

The concern is of course that the venting will move the projectile prematurely before the valve open. The advantage I see in this design is 100% air consumption efficiency as both the air from the pilot and the valve are used to push the projectile. Could it be that it also help opening the valve, creating a pressure differential?

What are your thoughts about that?

[youtube]http://www.youtube.com/watch?v=kF9ZdBmOAPs[/youtube]

[youtube]http://www.youtube.com/watch?v=y59cmRFzob8[/youtube]
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Re: blow forward pop-off valve

Unread postAuthor: jackssmirkingrevenge » Thu Nov 17, 2011 8:49 am

What LeMaudit didn't mention is that the outer casing was originally the core of a small nuclear reactor ;)

LeMaudit wrote:The concern is of course that the venting will move the projectile prematurely before the valve open. The advantage I see in this design is 100% air consumption efficiency as both the air from the pilot and the valve are used to push the projectile. Could it be that it also help opening the valve, creating a pressure differential?


A light detent would be the obvious solution, but...

Also, for the pressure differential to work, you have to be sure that air doesn't go back into the pilot, reclosing the piston...
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Unread postAuthor: LeMaudit » Thu Nov 17, 2011 8:58 am

Ah true... I forgot to mention that... :lol:
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Unread postAuthor: Brian the brain » Thu Nov 17, 2011 3:08 pm

When I see that slowmo I would say there will be no premature movement of the ammo...

Great experiment!
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Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

Can't ask for a better compliment!!
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Unread postAuthor: MrCrowley » Thu Nov 17, 2011 3:35 pm

Damn, that's awesome :shock:

Looking forward to seeing this finished.
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Unread postAuthor: Zeus » Thu Nov 17, 2011 4:37 pm

It wouldn't surprise me if the case was an old fusor.

Excellent work, shiny and clever, I look forward to the implementation of it.
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Unread postAuthor: iknowmy3tables » Thu Nov 17, 2011 5:08 pm

Maybe if you paired this valve with certain blow-forward breech the pilot volume would just help move the breech rather than propelling the projectile prematurely

do you have any basic diagrams for the internals of this valve?
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Unread postAuthor: LeMaudit » Thu Nov 17, 2011 6:06 pm

thanks guys, glad you like it.

After a day playing ratatatatak with it, the little tip broke to my amazement... it's brass damnit! I guess I underestimated the force involved :D

The force involved by the pilot breach is very weak, you can hold it with you pinky. No way to move something significant with it.

I'm going to make another one, more compact. This one was really (shiny) bits and pieces assembled (3 aluminum plugs bolted together from my scrap box in fact), with lots of trials and experiments before I reach this working state.

And I'll put a barrel on the next one :wink:
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Unread postAuthor: POLAND_SPUD » Thu Nov 17, 2011 6:41 pm

interesting... any chance to see a diagram showing all the parts ??
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Unread postAuthor: LeMaudit » Thu Nov 17, 2011 6:53 pm

any chance to see a diagram showing all the parts ??


I'll work on it. This one is just like the 10th iteration of a mechanism that evolved step by step, some of the internals make absolutely no sense and should be optimized :lol:

But I would still like to know your opinion about the possible nasty or goody side effects for venting the pilot inside the barrel... as I'm rebuilding one...

Or maybe ideas to be able to exhibit the consequences (like air turbulences) about it?
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Unread postAuthor: warhead052 » Thu Nov 17, 2011 8:17 pm

How small is the next one going to be? Nice job on this one though.
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Unread postAuthor: Gun Freak » Thu Nov 17, 2011 9:05 pm

I'd also like an internal diagram :wink: MS paint is fine :D Nice work!
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Unread postAuthor: LeMaudit » Thu Nov 17, 2011 9:25 pm

How small... dunno yet... less nuclear I guess...

all right all right, here's a diagram. The conic piston head was part of a previous experiment, next piston will have a nice flat head, easier to build and seal.
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Unread postAuthor: Brian the brain » Fri Nov 18, 2011 2:38 pm

I think the dimensions of the centerpiece are a bit off.
It won't work like this....
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Gun Freak wrote:
Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

Can't ask for a better compliment!!
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Unread postAuthor: jackssmirkingrevenge » Fri Nov 18, 2011 3:47 pm

Brian the brain wrote:I think the dimensions of the centerpiece are a bit off.
It won't work like this....


Yes it will. Pressurise, bolt moves forward, leaks pilot, piston fires.

It doesn't strictly "pop", which I don't like, but you can't argue it doesn't work ;)
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