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Coaxial endcap

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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Coaxial endcap

Unread postAuthor: Yonderknight » Thu Aug 31, 2006 11:22 pm

Hi,

I'm planning on making a GolfBall coaxial with a piston valve. I noticed that to cap off the valve-end of the gun, many people use plugs with screws to secure it. When looking around my local hardware store, I don't think I saw any plugs. Would there be any difference in using a plug than female adapter and a threaded plug, or maybe an endcap instead? I'm planning on using a spring, so I'm afraid if I hotglue the spring to a threaded encap it would be difficult to screw on.

Also, how does the cap or plug seal without any glue?

Thanks in advance!
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Unread postAuthor: )DEMON( » Fri Sep 01, 2006 12:04 am

A male and female adapter would be better because it would be the same pressure rating as your cannon. It will also look better. It would be better to use a male and female adapter than an endcap because you would be able to take it off , and endcap would be fixed. Heres a link to a cannon which uses a male and female adapter in the front: http://spudshot.com/Forum/viewtopic.php?t=35

They seal the plugs with o rings, the screws hold the plug in place. The Oring is on the chamber side of the screws so that air doesn't leak from the screws.
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Unread postAuthor: Yonderknight » Fri Sep 01, 2006 1:10 am

Hrmm, thanks a lot. It seems a lot easier to go with a threaded plug then. Do you think I should hot glue the spring to the threaded adapter? It would seem hard to get it to screw on with a spring there, but I don't really know.

Thanks again.
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Unread postAuthor: )DEMON( » Fri Sep 01, 2006 4:16 am

They don't sell them like that, you have to get a female adapter and reduce it to the size of your barrel. You shouldn't need to hot glue the spring, but if there is a problem then sort it out.

What exactly do you mean by hot glue the spring to the threaded adapter?
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Unread postAuthor: Yonderknight » Fri Sep 01, 2006 1:18 pm

Oops, by threaded adapter I meant threaded plug, sorry.
I'm having a little trouble explaining. Let me draw a quick diagram.

http://www.c-41productions.com/Henry/gbCoaxial.bmp

I was looking at a tutorial on BCVids on a barrel sealing piston valve, and the guy used a plug as the cap. He glued the spring to the plug and to the piston, and then used screws to hold the plug in place. I was wondering if it would be hard to screw the endcap on with a spring glued to it. Maybe I can just glue a small ring to the thread plug to hold the spring in place. I want to stay simple.
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Unread postAuthor: )DEMON( » Fri Sep 01, 2006 1:31 pm

You will need a wider spring. The bcvids tutorial is a barrel sealing valve, this is almost the same thing except it is a coaxial piston. You don't need a threaded plug, you need a reducer so you can add an exhaust valve and a fill valve. Make sure all the parts you get are pressure rated. Do you understand now?
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Unread postAuthor: Yonderknight » Fri Sep 01, 2006 1:56 pm

Yeah, I see now. I was just planning on having a blowgun and schrader drilled somewhere on the side of the end behind the piston. I guess I can just use a reducer bushing and have a 1" pipe or something coming out of that and drill the schrader and blowgun into there, that way they won't get in the way of the piston.

Thanks for all the help!
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Unread postAuthor: )DEMON( » Fri Sep 01, 2006 2:04 pm

Why drill extra holes in your cannon? Get some metal fittings and use the one port, the one behind the piston, and fix everything to it. That way you drill no holes. Just becarefull how much space is behind the piston, you want to have as little space as possible, your gun will preform better.
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Unread postAuthor: Yonderknight » Fri Sep 01, 2006 2:50 pm

Hrmm ok. I've rethought about the design, and here's what I cam up with:
http://www.c-41productions.com/Henry/GBCoaxial2.bmp

Will that work? Sorry, I'm a n00b with PVC. Thanks again =).
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Unread postAuthor: noname » Fri Sep 01, 2006 7:48 pm

I wouldn't expect that to work, but that's just me. That piston will spin and is not stable at all, and there is no way a blowgun can vent that much air fast enough.
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Unread postAuthor: Yonderknight » Fri Sep 01, 2006 8:05 pm

Well, the diagram isn't to scale. I could use a thinner pipe I guess. The piston will be a pretty thick hot glue piston, what do you mean by not stable?

Does the overall design need changing, or just the details? I just want something very simple that works, I don't care too much about performance since it's going to be a small gun anyways. Thanks!
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Unread postAuthor: Shrimphead » Fri Sep 01, 2006 8:25 pm

If a piston has room between it and the walls, and isn't very long, then it can wobble, causing it to be on an angle. This could keep it from sealing the barrel well. You should consider a longer piston and a larger pilot valve.
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Unread postAuthor: Yonderknight » Fri Sep 01, 2006 8:33 pm

As I said, the drawing isn't to scale, I just whipped it up really quick in paint. I'll be sure to have a very nice fitting piston. I don't feel like spending more money on a sprinkler valve as a pilot valve, and I don't like ball valves because your aim gets shifted if you try to open it quickly, and it's uncomfortable to open. I'll try to keep the area behind the piston to a minimum.

Thanks for all the replies =).


Wow, 3" fittings are more expensive than I thought.
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Unread postAuthor: noname » Sat Sep 02, 2006 12:18 pm

Use a modified sprinkler valve as a pilot if you have that much volume behind the piston. And make the piston at least 4 inches long or you are going to have problems.
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