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Air tank sealing problem.

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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Air tank sealing problem.

Unread postAuthor: warhead052 » Thu Mar 31, 2011 11:28 am

What should I use to reseal my pvc air tank? I have 15 more joints to seal, and I ran out of epoxy. Anything that would be a common house hold item that I could use? I have some pvc cement if that helps?
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Unread postAuthor: Crna Legija » Thu Mar 31, 2011 11:32 am

GET THE EPOXY OFF AND USE PVC PRIMER AND GLUE!!!!!!!!!!!!!! QUICK

its the only way to glue pvc together safely unless you live in a epoxy cave :lol:
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Unread postAuthor: warhead052 » Thu Mar 31, 2011 11:40 am

I have the pvc cement already in place. The airtank has been cemented, but it wont hold pressure above 2 bar. I expoxied one spot where it was leaking, and it sealed it; but then another spot opened up. Any suggestions for that?
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Unread postAuthor: Crna Legija » Thu Mar 31, 2011 11:46 am

did you do a 1/4 turn of the fitting after you pushed the fitting down allthe way?

make a vacuum in the tank and let the epoxy get sucked in thats the best way imo
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Unread postAuthor: warhead052 » Thu Mar 31, 2011 11:49 am

Yeah, I did a 1/4 turn. Its the joints for sure though, and I dont know exactly where, so I just put epoxy around the entire joint. I am getting a big thing of epoxy some time soon, and I am gonna seal it, then try it again. If you have any ideas, let me know.
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Unread postAuthor: Technician1002 » Thu Mar 31, 2011 12:01 pm

I would suggest starting over. If air is getting into the joints, it indicates areas where the two surfaces are not connected. This is a sure sign of DANGER in a pressurized chamber.

Any joint that is leaking needs to be discarded before it blows apart.
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Unread postAuthor: warhead052 » Thu Mar 31, 2011 12:06 pm

Its not a bad leak, honestly. I have put screws into it to keep the joints from blowing apart, and I think that may be the source of the leak. But I am still going to epoxy everything. It cost me too much time and effort to discard, so I will take my chances....
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Unread postAuthor: MrCrowley » Thu Mar 31, 2011 2:18 pm

Ugh. Start over. You do not want to be playing with this death trap. I'm not sure if you're aware of how dangerous PVC can be when it fails but you definitely should not be saying "I'll take my chances". You could lose an eye so freakin' easily it's not even funny.

The only reason I use PVC is because it's sort of cheap, light (compared to metals) and available but its failure characteristics scare the crap out of me.

I'm assuming you haven't applied the PVC cement properly or the PVC cement is past its used-by date. Pick up a new jar of PVC cement (that is for PRESSURE joints) and a jar of PVC primer (which you HAVE to use) and carefully read the instructions on the back.

I'm not sure if you realise but by drilling holes in to the PVC, you significantly weaken it and you should be worried of it fracturing. Did you test the chamber without screws in the PVC? I don't understand why you put screws in the PVC to "keep the joints from blowing apart", that's what primer and glue are for.
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Unread postAuthor: warhead052 » Thu Mar 31, 2011 2:22 pm

I tested everything, about 10 times each. The leak is actually pretty new, started about 6 hours ago. Its since stopped, and holds air, but honestly, I wont even take this thing past 50 psi simply because I dont want fatiuge to get to it... The joints are holding pretty well, and my mom is going to kill me if I buy more pvc. I will have to wait for my dad to get more before I can do anything else... Sorry guys... I am aware of the death trap, a friend of mine was paralyzed because of a pvc explosion, but he was kinda asking for it... Pressurizing it to 2,000 and then strapping it on his back... Idiot. But honestly, I will take my chances, this wont back fire on me. If it does, I will come back with a full apology. I managed to reglue everything by the way, and its stopped leaking.
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Unread postAuthor: Technician1002 » Thu Mar 31, 2011 3:08 pm

Its not a bad leak, honestly. I have put screws into it to keep the joints from blowing apart


Now you tell me you put holes in it and are surprised it leaks.. :roll:
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Unread postAuthor: warhead052 » Thu Mar 31, 2011 3:21 pm

I sealed the screw holes with epoxy when I re glued everything... I guess it was the screws that caused the leaks...
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Unread postAuthor: saefroch » Thu Mar 31, 2011 3:56 pm

Have you identified the location(s) of the leak(s)?
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Unread postAuthor: MrCrowley » Thu Mar 31, 2011 4:59 pm

I still don't get why you put scews in the joints. So, why did you put screws in the PVC joints before you knew the joints leaked?
If anything, the screws would make the joint weaker, not stronger.

edit: By the way, how did you reglue everything? If that means you just put some glue around the edge of the fittings where they were leaking, it still could mean your joints are weak since there could be gaps where there is no glue on some surface parts of the joints.
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Unread postAuthor: mark.f » Thu Mar 31, 2011 6:32 pm

I guess this is a good life lesson. Take the time to do things right the first time, so there won't be a next time.

Seriously, just wait to get some new PVC, glue, and primer and redo it. I know the wait may be torture, but when you get older you'll find yourself waiting two years or more at times before investing in free time "projects". :wink: For instance, I've got multiple drawings of my next project, along with calculations, dimensions, parts lists, procedures, you name it. When will I be able to finish this project? Who knows? I plan on saving up for some machinery and tooling to do the project correctly, so probably a couple of years, most likely.

In short, patience is a virtue. Hell, you may change your mind between here and there and decide to go with metal construction in the meantime, bypassing glues and low pressure ratings altogether. :lol:
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Unread postAuthor: warhead052 » Thu Mar 31, 2011 8:15 pm

@saefroch Re-read my last post.

@Mrcrowley The screws went in before I knew about the leaks... They went in incase the glue busted....

@mark.f This is a good lesson, never try to make this sort of airtank again, until I get better tools and more money to spend on it.
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