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more help please with t-shirt gun not sealing properly

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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more help please with t-shirt gun not sealing properly

Unread postAuthor: JDP12 » Wed Sep 24, 2008 8:12 am

Hey all, i got some new rubber and a washer for my t-shirt gun but i still can't get it to work quite right. Right now the barrel seals almost all the way except i can hear it is still leaking out the barrel a bit. it sounds like its only leaking from one spot however so i need help to isolate that,
i think the rubber might not be even over the face of the piston so I will look at that when i get home.


and the second problem is that i can't get my main chamber to fill up. the pilot volume fills up and fires fine, but the main chamber never fills- i think i might have to drill a large hole in the side of the coupler that forms the piston?

Please take a look at the pictures and tell me what you think.

<img src="http://i157.photobucket.com/albums/t79/justhavinagoodtime/DSC00309.jpg">

<img src="http://i157.photobucket.com/albums/t79/justhavinagoodtime/DSC00310.jpg">

<img src="http://i157.photobucket.com/albums/t79/justhavinagoodtime/DSC00311.jpg">

<img src="http://i157.photobucket.com/albums/t79/justhavinagoodtime/DSC00312.jpg">

<img src="http://i157.photobucket.com/albums/t79/justhavinagoodtime/DSC00313.jpg">

<img src="http://i157.photobucket.com/albums/t79/justhavinagoodtime/DSC00314.jpg">

THIS ONE IS OF PISTON IN TEE

<img src="http://i157.photobucket.com/albums/t79/justhavinagoodtime/DSC00315.jpg">
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Unread postAuthor: mark.f » Wed Sep 24, 2008 8:28 am

Can air get around the piston?

Also, it doesn't look like the sealing face on that piston is very square. That would be the first place to start.... or just get a much thicker gasketing material.
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Unread postAuthor: starman » Wed Sep 24, 2008 9:13 am

That irregular looking "washer" holding down the rubber may also be a problem for you. Also, it looks like you're going to be leaking a LOT of air around the piston when you fire.

Why do you believe you aren't filling your chamber? You don't show the full chamber configuration but unless it's totally sealed off, air should easily find a way to get in there without drilling extra holes.
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Unread postAuthor: JDP12 » Wed Sep 24, 2008 12:03 pm

ok the washer had to be hand cut out of an electrical box cover because home depot didnt have any big ones.

and i'm not filling the chamber and i know it because when i fire it, no air comes out of the barrel at all, course it could be leaking out around the piston..

but why does it look like i'll be leaking a lot of air around the piston??

POSSIBLE THEORY: I reexamined it, and I think what may be happening is that the air is getting to the chamber okay, but its leaking out the barrel. when i shut off the filling air, air still hisses out teh barrel for some time so i think that that might be all the air from the chamber leaking out? What do you think?

and this has to be done by friday, that is my FINAL deadline that i got so it needs to be done
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Unread postAuthor: Pilgrimman » Wed Sep 24, 2008 12:58 pm

The problem may be lack of surface area on the front of the piston. The air will just go out the pilot if the piston doesn't open. Other than that, and what has been said, I have no other suggestions.
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Unread postAuthor: MrCrowley » Wed Sep 24, 2008 1:57 pm

I'd say air is leaking out the bolt in the front of your piston.

But i'd recommend making a whole new piston all together, yours doesn't exactly look strong or efficient and will probably be a [female doggy] to get working with that sanding job on the body.
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Unread postAuthor: JDP12 » Wed Sep 24, 2008 3:57 pm

ok well then what should i use for a piston- that was a 3" coupler, maybe a 3" PVC piece that has electrical tape on it so it fits in the 4" pipe

i need recommendations for a piston that will fit in 4" pipe, tonight please

i know LikimysCrotchus5 used a 3' endcap, but how did he get it sanded down so smooth?

I had to cut mine down on a bandsaw

but basically i need ideas, pronto, stat, ASAP
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Unread postAuthor: LikimysCrotchus5 » Wed Sep 24, 2008 5:39 pm

Well, my endcap was already pretty smooth, so it was pretty good, but it still has friction and i fear that the piston will get stuck one day.

But anyway, i was at a hardware store and i took a 3 inch coupler, out of curiosity, and it ended up fitting perfectly in 4 inch pipe, but not the pipe thats in my cannon.

It all comes down to the manufacturer. Some endcaps, couplers, and pipe have different ID and OD. So just fool around with something and see if it fits.

But you need a bigger washer to cover the whole gap that you see so it can provide equal force. What i actually ended up using was a home-made washer cut from sheet metal. So try that as a washer for support as well.
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Unread postAuthor: JDP12 » Wed Sep 24, 2008 6:05 pm

k do you think the bolt hole could be leaking as well?
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Unread postAuthor: LikimysCrotchus5 » Wed Sep 24, 2008 8:54 pm

Yea, you should teflon it. When asked me for my opinion on this today, i remembered that my 4SPC had leaks, so i just took it out, filled it up, and tried to find the leaks. I already knew where some of them were and i knew it was leaking through the barrel. So.. what i did was put my hand down the breach to feel for the leak. I felt around the sides where the sealing face touches the sealing pipe, and there was no leak around there, but i still felt air coming from somewhere. So i felt the center, where the bolt was and although it was a little hard to deduce, i am pretty sure that its leaking through the bolt, so now im gonna have to teflon that.

Just goes to show ya. :roll:
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Unread postAuthor: blind909 » Wed Sep 24, 2008 9:28 pm

Sorry if this has been mentioned before, but you could also Try Adding some petroleum jelly(vasaline) to your sealing face, It worked when my COAX'S Piston was not sealing, but you will have to keep doing that every week or so, and/or epoxy over the entire bolt assembly.
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Unread postAuthor: iisthemuffin » Wed Sep 24, 2008 9:39 pm

I tihnk your problem is the entire piston.
Your sealing face looks very off center and your piston is very uneven.

If you look at the picture where the piston is in the tee: On one side it looks like it fits too tight and on the other it looks too lose.

You could buy a crap load of epoxy and fill a 4 inch pipe with it and use that as a piston.

Just go to your grocery store and try to find some round object to fit in the pipe. I would try a place that sells bulk items. If you live in the states try sams club or maybe a GFS. Look at there cans and other stuff.
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Unread postAuthor: JDP12 » Wed Sep 24, 2008 9:46 pm

I started a new thread about the success of this gun, please look at it.

Thanks
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