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High Effeciency Piston

A place to ask general spud cannon related questions.
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High Effeciency Piston

Unread postAuthor: Flash » Fri Feb 15, 2008 3:54 pm

Here's a 3D model of a piston that I designed. I made it to be used with a barrel sealing or coaxial cannon. The main thing is that the equalization hole is actually a homemade check valve that has a smaller surface area on the side where air enters, giving it a possibly low cracking pressure. Its also made to be less long than most pistons, making it weigh less and move back faster.

EDIT: How do I embed a video from photobucket?

<embed>
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Last edited by Flash on Fri Feb 15, 2008 4:54 pm, edited 4 times in total.
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Unread postAuthor: MrCrowley » Fri Feb 15, 2008 3:57 pm

Need help with inserting the model?

What format is it?
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Unread postAuthor: Flash » Fri Feb 15, 2008 4:03 pm

Need help with inserting the model?

What format is it?


Its one of those videos made on Photobucket. I'll post a picture for now.
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Unread postAuthor: MrCrowley » Fri Feb 15, 2008 4:37 pm

Link to the video, and then for us to view it we have to right click the link and open a new tab/window.
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Unread postAuthor: Flash » Fri Feb 15, 2008 5:03 pm

I wasn't able to embed it, so here's the link.

Image
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Unread postAuthor: Hawkeye » Fri Feb 15, 2008 6:45 pm

The lighter one way valve piston has already been done with a floating o-ring which leaks as the gun is pressurized and seals 100 % as soon as the piston starts moving back.
I can't really tell what materials your model would be made of but the red portion looks like it might just be pulled out of place.
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Unread postAuthor: Flash » Fri Feb 15, 2008 7:41 pm

Do you have a link to that piston? It sounds pretty cool.

And what do you mean by it being pulled out of place? Do you mean that it be pushed out of the outside blue piece from the pressure? I never took into consideration the possibility of it being exposed to high pressures (like in copper cannons), just mid pressures to be used in nerf and paintball guns.
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Unread postAuthor: jackssmirkingrevenge » Sat Feb 16, 2008 1:31 am

Flash wrote:Do you have a link to that piston? It sounds pretty cool.


The piston would look something like this:

Image

And the "floating o-ring which leaks as the gun is pressurized and seals 100 % as soon as the piston starts moving back" idea is exactly what is used in the piston of most manual pumps:

Image
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Unread postAuthor: Hawkeye » Sat Feb 16, 2008 9:11 am

Yes, it is just based on the bike pump piston. I make these pistons from two large tap washers, a smaller central spacer with the o-ring around it and a sealing face glued on.
Pretty sure Rag makes them in similar fashion.
Jack, I think you'll notice that your diagram has the grooves on the wrong side of the o-ring. ;)
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Unread postAuthor: pizlo » Sat Feb 16, 2008 9:24 am

It works Exactly like a nerf plunger. When it travels forward(backwards I guess) the o-ring is pushed against the solid ridge of plastic and makes a seal, but when in moves the other way the O-ring is pushed against the ridge with the grooves, and the grooves make it so no seal can be achieved.
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Unread postAuthor: Gippeto » Sat Feb 16, 2008 11:03 am

I'm curious;

If you guys can make a groove for an o-ring, why don't you use a u-cup seal? No need for an equalization hole or check valve. They are wear compensating. The greater the pressure differential, the better they seal.

Your piston would work very much like a qev, and built from suitable materials, would tolerate much higher pressures.
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Unread postAuthor: jackssmirkingrevenge » Sat Feb 16, 2008 12:32 pm

Hawkeye wrote:Jack, I think you'll notice that your diagram has the grooves on the wrong side of the o-ring. ;)


Filling air from behind (coming from the right in the diagram) the piston pushes the o-ring in the groove and allows the air to leak past. When the pilot is opened, the o-ring pushes against the non-grooved section of the piston, preventing air in the chamber from leaking into the pilot area.

How is it the wrong side?

On another tangent, this had been my idea for a high efficieny piston - basically, the piston is in two parts, the purple section starts to accelerate when the pilot is opened, so that instead of starting to open gradually, the red portion sealing the barrel is yanked open suddenly when the purple part hits it. The diagram is not to scale, the purple section can afford to be a little larger in diameter.
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Unread postAuthor: Hawkeye » Sat Feb 16, 2008 2:19 pm

It will still work that way, but I think if you reverse the side the grooves are on it will work better.
When the piston starts to move backwards it should have the o-ring seal against the solid rim. The air acting against the piston face is going to shove the body of the piston back faster than the o-ring.
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Unread postAuthor: jackssmirkingrevenge » Sat Feb 16, 2008 2:29 pm

Hawkeye wrote:The air acting against the piston face is going to shove the body of the piston back faster than the o-ring.


If that were the case, how do you explain the fact that pump heads use the configuration I illustrated?
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Unread postAuthor: Gippeto » Sat Feb 16, 2008 2:31 pm

I can see that drastically reducing pilot volume. Still kind of complicated to build, but sound in theory.

My idea of a high efficiency piston.
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