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Modified sprinkler valve - epoxy issue

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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Modified sprinkler valve - epoxy issue

Unread postAuthor: yman » Sat Jul 30, 2011 12:21 pm

I just finished(maybe) my first pneumatic tennis ball launcher - a simple, over-under design with a modified Rainbird 100-DV valve and blowgun trigger. I'm having a problem with the trigger, though. I drilled and tapped a 1/8 NPT hole for the trigger, and used a plastic epoxy to attach a brass nipple by applying epoxy to the threads of the nipple before twisting it into place, then on the inner end of the nipple after it was in place. I attached a 90 degree street elbow and then the trigger, using pipe tape between each.

Long story short, the nipple didn't hold. After I attached the blowgun trigger, it came apart were the nipple was epoxied to the threaded valve hole. The epoxy didn't hold, and I'm guessing I must have cross-threaded the nipple when testing the threaded hole, since the threaded hole also failed to hold the nipple.

I'm about to retry it, but was hoping for some advice. Is there something I can do to strengthen this joint where the nipple goes into the valve? Should I use a particular epoxy, or should I skip epoxy and just use pipe tape to get a tight seal? Any other advice?

Thanks.
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Unread postAuthor: mattyzip77 » Sat Jul 30, 2011 12:29 pm

Try using j b weld. I think its 100 times better than epoxy! If your hole is too big, put a fitting in it to get to the size you need. Did you watch any of the tutorials on here?? They are pretty good. You should use a tap but you dont have to. If you make the hole the right size it should tap itself!!!

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Unread postAuthor: saefroch » Sat Jul 30, 2011 1:30 pm

Did you just epoxy the surface? Was the epoxy fully cured and not sticky?
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Re: Modified sprinkler valve - epoxy issue

Unread postAuthor: jackssmirkingrevenge » Sat Jul 30, 2011 1:35 pm

yman wrote:a plastic epoxy


Link to the product? Doesn't sound like you've been using the right stuff.
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Unread postAuthor: jsefcik » Sat Jul 30, 2011 3:27 pm

Jb weld all the way, ok people say it doesnt stick to plastic very well, pipe must be clean and free of dirt and, ive used it in my gun that ive had up to 150 psi no problems!!!!
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Unread postAuthor: MrCrowley » Sat Jul 30, 2011 5:26 pm

mattyzip77 wrote:Try using j b weld. I think its 100 times better than epoxy

JB-Weld is epoxy :roll:


yman,

Can you link us to the epoxy product you used? Also, how long did you wait for it to cure? Most 'good' epoxies take at least 24 hours.

Personally I find that with JB-Weld it is better to wait like 72 hours than 24 hours because it seems stronger and that araldite is much better for bonding to plastics. JB-Weld does also seem to chip and fracture more easily during the first few days.

You really can't go wrong with an araldite epoxy.
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Unread postAuthor: saefroch » Sat Jul 30, 2011 6:09 pm

24 hours at room temperature maybe, but if you cut off the corner of a plastic bag, inject the epoxy in, dip it in hot water until it becomes very thin, mix with a disposable object for 20 seconds, then heat the final product in a toaster or oven at about 100F (just turning the light on will get most ovens up to about that), even epoxies that are marked for 2 hours curing usually cure in about 30 minutes.
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Unread postAuthor: yman » Sat Jul 30, 2011 9:13 pm

Sorry about that - guess I should've included some more details.

The epoxy was a two-part plastic epoxy I picked up at Home Depot, but I don't have the container anymore, so I don't know the name. I had let it cure for @ 30 hours when I handled it. didn't put much pressure on the trigger and it came off fairly easily, which is why I was guessing I may have stripped the threads when I put the nipple in. The gun wasn't even pressurized ... it just came off.

I think I'll try it again with JB Weld, leaving plenty of time for it to cure. Do I just slather the nipple threads with the epoxy and screw it into place, or is there some other technique I should use?

Thanks, all!
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Unread postAuthor: Gun Freak » Sat Jul 30, 2011 10:15 pm

Make sure you mix it very thoroughly.
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Unread postAuthor: mattyzip77 » Sat Jul 30, 2011 10:16 pm

j b weld it on and around the whole inner part and on and around the outer part of the nipple. where did you make the hole?? in the center of the valve, or where the bleed screw was??? If you made it where the bleed screw was, than just j b weld that whole hole, and start over in the middle, and or you could even do that vice versa if you wanted too!!!
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Unread postAuthor: saefroch » Sun Jul 31, 2011 10:59 am

Did you roughen up all surfaces you were trying to adhere to? Mixing is key, if you have the right amounts of both and after curing for a while it's still sticky or soft, you didn't mix it well enough.
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Unread postAuthor: SpudBlaster15 » Sun Jul 31, 2011 5:19 pm

Why is everyone going on about epoxy? The OP needs to take a look at the real problem: His threads.

Properly tapped NPT threads should hold the fitting securely without the need for any adhesive. You either drilled the hole too large, threaded the tap through too far, or used the wrong size tap. Figure out the issue, go buy another valve, and redo it properly instead of trying to jury rig a flawed setup with epoxy.
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Unread postAuthor: jsefcik » Sun Jul 31, 2011 8:05 pm

Just mix equal parts
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Unread postAuthor: Gun Freak » Sun Jul 31, 2011 10:05 pm

jsefcik wrote:Just mix equal parts

Did you read what SB15 just said? Lol
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Unread postAuthor: mattyzip77 » Sun Jul 31, 2011 10:07 pm

can someone lock this topic already??????????????
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