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Need an airtight reopenable 4" coupler - how?

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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Need an airtight reopenable 4" coupler - how?

Unread postAuthor: Coodude26 » Mon Nov 16, 2009 2:59 am

I need to join two pieces of 4" pvc in a way that is straight, airtight, simple, and most importantly, dismountable.

I have a 4" inline barrel-sealed piston cannon, works amazingly powerfully at 10psi, but I'm having a problem (luckily I know exactly what it is, and how to fix it). So what I'm going to do is cut the outside 4" pipe, fix it, and put in this remountable 4" coupler & seal it all up. But I don't know exactly how to do that.

Yes I'm stupid for installing the "resealable" part of the gun after sealing it...just bare with me. My major flaw is that I only ever learn from first hand experience...

I thought about using several bolts around the coupler, but they are tricky to seal around the threads for multiple uses, and there is always the issue of the PVC warping & leaving gaps.

If you guys have any ideas (and I mean any, I'm terrible at brainstorming), pitch it out here. Thanks in advance. I really do appreciate the brains of this forum.
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Plumbers have a funny definition of half an inch...


[quote=chinnerz]once my and one of my mates spent a whole day modding a nurf pistol.... it ended up shooting 1 extra meter and had an awesome paint job. (not rly worth it) [/quote]

/\why I don't like Nerf...
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Unread postAuthor: Crna Legija » Mon Nov 16, 2009 4:56 am

o-rings
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Unread postAuthor: iknowmy3tables » Mon Nov 16, 2009 10:47 am

well that will seal it but what about keeping it on, any one know about some of the products used by construction teams for temporary water works

the most commonly used solution is get a male and female threaded adapter, might cost you a pretty penny for 4" ones but if you planned to make it open able in the first place you probably would have bought them instead of a coupler
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Re: Need an airtight reopenable 4" coupler - how?

Unread postAuthor: boyntonstu » Mon Nov 16, 2009 10:59 am

Coodude26 wrote:I need to join two pieces of 4" pvc in a way that is straight, airtight, simple, and most importantly, dismountable.

I have a 4" inline barrel-sealed piston cannon, works amazingly powerfully at 10psi, but I'm having a problem (luckily I know exactly what it is, and how to fix it). So what I'm going to do is cut the outside 4" pipe, fix it, and put in this remountable 4" coupler & seal it all up. But I don't know exactly how to do that.

Yes I'm stupid for installing the "resealable" part of the gun after sealing it...just bare with me. My major flaw is that I only ever learn from first hand experience...

I thought about using several bolts around the coupler, but they are tricky to seal around the threads for multiple uses, and there is always the issue of the PVC warping & leaving gaps.

If you guys have any ideas (and I mean any, I'm terrible at brainstorming), pitch it out here. Thanks in advance. I really do appreciate the brains of this forum.


"just bare with me."

Why are we undressing?
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Unread postAuthor: Coodude26 » Mon Nov 16, 2009 6:34 pm

-_- wrote:o-rings
(message to small)


I had hoped you would be more specific than that. Maybe you don't get what I'm saying.

Say you have a piece of 4" pipe. Now cut it in half, and make something that can re-attach these pieces & is removable + airtight.


iknowmy3tables wrote:well that will seal it but what about keeping it on, any one know about some of the products used by construction teams for temporary water works

the most commonly used solution is get a male and female threaded adapter, might cost you a pretty penny for 4" ones but if you planned to make it open able in the first place you probably would have bought them instead of a coupler


I might have been dealing with some really poor quality joints, but in the past I've used these and they've been extremely un-airtight. And I mean, VERY.

boyntonstu wrote:"just bare with me."

Why are we undressing?


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Plumbers have a funny definition of half an inch...


[quote=chinnerz]once my and one of my mates spent a whole day modding a nurf pistol.... it ended up shooting 1 extra meter and had an awesome paint job. (not rly worth it) [/quote]

/\why I don't like Nerf...
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Unread postAuthor: kjjohn » Mon Nov 16, 2009 8:07 pm

camlock adapters, if they come that big
otherwise, threads
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Unread postAuthor: iknowmy3tables » Mon Nov 16, 2009 8:28 pm

very unair tight? socket welds or threads if it's the socket welds then it's probably you and you need to learn proper technique if it's the threads you need to use more Teflon tape.
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Unread postAuthor: Coodude26 » Tue Nov 17, 2009 1:10 am

iknowmy3tables wrote:very unair tight? socket welds or threads if it's the socket welds then it's probably you and you need to learn proper technique if it's the threads you need to use more Teflon tape.


I meant the threads, and I have taken that course, so don't worry. And I can never find decent threads, the ones I can find don't seem to be meant for air pressure as there is a lot of leeway between the threads and they're relatively far-spaced.
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Plumbers have a funny definition of half an inch...


[quote=chinnerz]once my and one of my mates spent a whole day modding a nurf pistol.... it ended up shooting 1 extra meter and had an awesome paint job. (not rly worth it) [/quote]

/\why I don't like Nerf...
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Unread postAuthor: iknowmy3tables » Tue Nov 17, 2009 2:47 pm

so are the threads a different gauge so they don't fit?, I doubt that you found any thread type for 4" pipe besides NPT (National Pipe Thread),
you do know that when you screw threads together there is supposed to be a gap, in other words the female threads don't completely cover the male threads on the adapter, right? and do you cover part of the male threads with at least 2 layers of Teflon tape right?
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Unread postAuthor: Coodude26 » Tue Nov 17, 2009 7:32 pm

iknowmy3tables wrote:so are the threads a different gauge so they don't fit?, I doubt that you found any thread type for 4" pipe besides NPT (National Pipe Thread),
you do know that when you screw threads together there is supposed to be a gap, in other words the female threads don't completely cover the male threads on the adapter, right? and do you cover part of the male threads with at least 2 layers of Teflon tape right?


The threads just aren't made to that great of tolerances - they're molded, not spun on a lathe. And yes I understand that but I was having trouble getting the things screwed on tight, it's not possible to get them all the way in without some kind of tool or leverage(/sexjoke) I'm making a seal with silicon, and with the teflon tape on, hopefully it'll be relatively airtight...
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Plumbers have a funny definition of half an inch...


[quote=chinnerz]once my and one of my mates spent a whole day modding a nurf pistol.... it ended up shooting 1 extra meter and had an awesome paint job. (not rly worth it) [/quote]

/\why I don't like Nerf...
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