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pvc elbow cracks

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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pvc elbow cracks

Unread postAuthor: pat123 » Sun Jul 08, 2007 6:33 pm

i pumped up my gun to 50 psi and fired it. it was the first time i shot it so i had it laying on the ground instead of holding it. when i fired it a piece of the elbow blew out. if I was holding it would have hit me in the face has anyone else had this problem. it was a 1/2 in Lasco elbow sch 40
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Unread postAuthor: homedepotpro » Sun Jul 08, 2007 6:45 pm

what does the gun look like, is there excessive stress on the elbow
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Unread postAuthor: frankrede » Sun Jul 08, 2007 6:46 pm

1/2" parts in my opinion are more brittle and the shock from the cannon going off may have stressed them too much.
If you were holding it,things may have worked different, because any force may have been absorbed by your body from the gun going off
Did you have any ammo in it?
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Unread postAuthor: Pilgrimman » Sun Jul 08, 2007 6:49 pm

1. Did you solvent weld it?
2. If you did, did you let it cure for 24 hours before pressurizing it?
3. Is the design putting stress on the elbow? (Like something sagging, or trying to bend it less or more than 90 degrees)
4. What kind of weather did you shoot in?
5. Is it PVC? If so, is it compatible with the rest of the gun?
6. Did you check for cracks or anything before buying it?
7. Did you use old cement or primer?

If you did all of the right stuff, the only problem I can think of is that you might not have enough surface area on your solvent weld, so it failed, or you somehow put shock on the elbow by dropping it or something. If it's a piston gun, your piston might have whacked the elbow, causing failure, but I've never heard of that happening. Good luck finding the problem! 8)
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Unread postAuthor: Modderxtrordanare » Sun Jul 08, 2007 6:51 pm

Pilgrimman wrote:5. Is it PVC? If so, is it compatible with the rest of the gun?


Look at the title of the thread. :wink:

It could always have been a manufacturing flaw though.
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Unread postAuthor: Pilgrimman » Sun Jul 08, 2007 6:59 pm

Look at the title of the thread.

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Unread postAuthor: pat123 » Sun Jul 08, 2007 7:30 pm

thanks for the help
i'll post pics of it tomorrow.
air is also leaking around my blowgun on my sprinkler valve after i get to about 30 psi. i've tried sealing it with everything i can think of but it still leaks

1. Did you solvent weld it?
yes i used primer and cement

2. If you did, did you let it cure for 24 hours before pressurizing it?
I let it cure for about three days before i shot it

3. Is the design putting stress on the elbow? (Like something sagging, or trying to bend it less or more than 90 degrees)
this maybe the problem but it wasn't sagging at all

4. What kind of weather did you shoot in?
it was
it was about 85 degrees

5. Is it PVC? If so, is it compatible with the rest of the gun?
yes it is all sch 40 pvc

6. Did you check for cracks or anything before buying it?
yeah i checked everything before i put it together

7. Did you use old cement or primer?
i just bought the primer the day before, the cements about a month old
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Unread postAuthor: Acdcmonkey1991 » Sun Jul 08, 2007 7:51 pm

I've had the exact same problem. That brand of fittings is just cheap...
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Unread postAuthor: Pilgrimman » Sun Jul 08, 2007 8:25 pm

For the blowgun, you did use teflon tape or something similar on the threads, right? If you still have problems, you might check the wiki, or the how-to on modding sprinkler valves. As I've never modded one, I can't really help you. Sorry! :oops:

About the elbow...

You might have had burrs or something caught in the elbow or on the end of the pipe when you welded them. That's the only reason I can think of at this point, other than buying parts from a lousy manufacturer.
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Unread postAuthor: pat123 » Sun Jul 08, 2007 9:36 pm

thanks :)
I have a elbow made by a different manufacturer i will put on tomorrow i have 2 elbow on my gun and the other one was a different brand and didn't break.

i have tried 4 different kinds of sealant on my blowgun and none keep it from leaking. what is the best thing to seal it with?
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Unread postAuthor: pat123 » Mon Jul 09, 2007 10:36 am

I took some pics of the gun and what broke
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Attachments
DCAM6425.JPG
this is what broke
DCAM6427.JPG
this is the gun
DCAM6428.JPG
it is leaking where all the epoxy is
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Unread postAuthor: Pilgrimman » Mon Jul 09, 2007 7:17 pm

The elbow might have failed due to excessive recoil forces (mostly muzzle climb bending the elbow. It compresses the outer part of the elbow, and PVC does not stand up to shock well.). I would recommend putting a connection between the barrel and chamber so that the recoil is more evenly distributed.

Also, I never asked... The PVC is pressure rated, right? I'm not assuming you're dumb, but you never know... :wink:

About the blowgun... is the leak between the valve and blowgun itself, or the hole where the solenoid used to be?
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Unread postAuthor: paaiyan » Mon Jul 09, 2007 7:22 pm

With that setup, it looks to me like the culprit was definitely stress on the elbow joint. When you fire, the recoil puts stress on that elbow basically bending it slightly outward and placing a lot of stress on that joint, I've heard from people that this is a big problem when you fire without a projectile, was there something in it when you fired?
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Unread postAuthor: noname » Mon Jul 09, 2007 7:51 pm

For sealing the blowgun, take the blowgun out and get all the epoxy off. Glob epoxy all over the nipple and then screw the blowgun in. It should seal up fine. Silicone sealant works even better in this application, but I guess epoxy would work.
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Unread postAuthor: paintballuh » Sat Jul 14, 2007 7:12 pm

IMO, i think it might have been because the valve is placed right before the elbows, the compressed air would have shot straight up hitting the elbows very hard, especially if the projectile was somewhat tight in the barrel, combine that with teh recoil, and the stress on the elbows from the weight of the barrel...but what do i know? im just a n00b...
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