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constant flow full auto :)

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: jackssmirkingrevenge » Tue Jan 13, 2009 6:55 pm

That's not how pop-off valves work though. In the case of the one I'm using, the porting is just under 6mm while the piston diameter is 10mm. This means that when closed, the spring only has to support the air pushing on the 6mm port, let's say around 4 lbs at 100 psi. Once the air gets past the port however, now the full area of the piston is exposed, so now those 100 psi are putting 12 lbs of force on the piston, which is much more than the spring can take so it "pops" allowing air through the vents until the pressure drops.
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Unread postAuthor: iknowmy3tables » Tue Jan 13, 2009 10:13 pm

I see now, but still this would only use half the pressure of the input, do you think this could work well though, the force of friction using the setup can be really high like 10lbs on the opening direction and 1lb in the closing direction
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Unread postAuthor: jackssmirkingrevenge » Wed Jan 14, 2009 1:40 am

iknowmy3tables wrote:I see now, but still this would only use half the pressure of the input, do you think this could work well though, the force of friction using the setup can be really high like 10lbs on the opening direction and 1lb in the closing direction


The problem is that once it begins to close, it encounters air resistance, making it liable to stay open and sound... well, flatulent. High friction on opening means that it will open slowly and therefore not gain enough momentum to return properly.

That's my 2 euro cents, but if you want to try it out and prove me wrong, go ahead. Whatever you do, make sure it's tweakable ;)
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Unread postAuthor: psycix » Wed Jan 14, 2009 1:44 pm

@ the high friction design

More friction = more heat
More friction = more wear
Automatic firing = Rapid subsequent shots

Combine and....
1- It will all melt
2- It will all wear down in no-time
3- While it wears down, the friction changes, requiring constant tweaking.
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Unread postAuthor: Brian the brain » Wed Jan 14, 2009 5:12 pm

You've just summed up the exact reasons why pressure actuated full auto is so hard to do..

Jack..I'm watching you bro! :wink:
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Unread postAuthor: psycix » Thu Jan 15, 2009 9:12 am

Indeed, almost all full auto's got those problems, and increasing friction only makes the problems larger.
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Unread postAuthor: jackssmirkingrevenge » Fri Nov 06, 2009 11:45 am

This is why I insist that anything that's going to be thrown out at work comes to me first :D

Yes, a brass 1" pop-off valve! I took it apart and it's got a bit of surface corrosion but it's to be expected given its years hooked up to a steam pump, but all it needs is a good clean et voila, I might just make that auto marble gun *muahahaha*

In case you're wondering, that tiny little thing in the middle is the 1/4" pop-off valve that's the original subject of this thread, for scale :)
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Unread postAuthor: psycix » Fri Nov 06, 2009 12:05 pm

*Whistle* Now that's a popoff!
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Unread postAuthor: jackssmirkingrevenge » Fri Nov 06, 2009 11:00 pm

psycix wrote:*Whistle* Now that's a popoff!


It certainly is :D needs some modding though to ensure it works like this though, but not much work. The important thing is that there is a strong body and spring that can deal with the larger areas involved, the rest is easy.

The seat is a full 1" diameter, meaning that 3/4" porting is just about right :) basically I'm going to fit a piston tube - 37mm, giving a piston:seat area ratio of more than 2:1 - to eliminate the dead space and cast a new lighter piston, going by the same principles as my other "rattlesnake" valves it should work a charm.

I'm not exactly sure what I'll be hooking it up to, but it will be big and it will need to be hooked up to a compressor :roll: :D
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Unread postAuthor: inonickname » Fri Nov 06, 2009 11:13 pm

Lucky- when I went to Bunnings and asked for pop-off valves I was shown pop-off valves for steam..not exactly what I wanted..

They ranged from $70-$100, so you got a good score there.

Why stay at a marble MG? Pilot for a GB MG or something larger.. I'll keep an eye on this I guess :lol:
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Unread postAuthor: jackssmirkingrevenge » Fri Nov 06, 2009 11:47 pm

The reason I never actually bought one so big was that they were so bloody expesnive so it was nice to get this as an early xmas present :D though I was pissed off to hear that several similar 3/4" valves had been thrown out in my absence :-/

Why stay at a marble MG? Pilot for a GB MG or something larger...


I can't abide by wasting this as a pilot, think of all the air going out of the back that could have been used to fire the projectile! These things eat air up at an insane rate but at least using it as a direct valve you know all that air is pushing your ammunition out.

It would probably still be very decent for golf balls if used in this manner though, hmmm... where does one buy cheap golf balls in quantity?
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Unread postAuthor: Lentamentalisk » Sat Nov 07, 2009 2:37 am

Ebay
600 golf balls for $40 including shipping. Not the best deal, but shipping is going to be a pain in the posterior no matter what. Look around, and you may find something better. Or, go to the local range, and see if you can buy used balls that they pick up that people leave behind.
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Unread postAuthor: POLAND_SPUD » Sat Nov 07, 2009 6:39 am

@JSR
wow that's nice

it would be cool if you could install an air compressor in your landrover... at least that will be able to provide enough flow and you won't have to worry so much about noise

well even if it can't be done, now you've got something to think about before buying a new car
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Unread postAuthor: psycix » Sat Nov 07, 2009 7:04 am

So when do you start casting? Or is it curing as we speak?
What is the effective valve porting?

it would be cool if you could install an air compressor in your landrover...
Psst... call it a Jeep! :P
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Unread postAuthor: jackssmirkingrevenge » Sat Nov 07, 2009 12:56 pm

POLAND_SPUD wrote:it would be cool if you could install an air compressor in your landrover... at least that will be able to provide enough flow and you won't have to worry so much about noise


I try to be discrete about my spudding, I don't think a vehicle mounted autocannon would be consistent with keeping a low profile :D

Psst... call it a Jeep!


gah!

Image

:D :D :D

I'm filling in the dead space for now, and making a chamber, to see how it fares with the standard piston. I'm keeping it as an "on the side" project for the moment as it was an unplanned development.
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