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metal on metal threads leak

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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metal on metal threads leak

Unread postAuthor: keep_it_real » Sun Feb 04, 2007 1:15 am

should I lubricate the metal on metal threads with petroleum jelly to stop them from leaking? Is this a common problem?
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Unread postAuthor: frankrede » Sun Feb 04, 2007 1:26 am

use Teflon, pipe thread sealant
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Unread postAuthor: SpudBlaster15 » Sun Feb 04, 2007 2:36 am

Any threaded joint has a tendancy to leak due to microscopic (or more obvious) surface imperfections. Teflon thread sealant tape is reccomended, due to its tendancy to "creep" (there is a more technical name but I dont know what it is). Creep refers to a case in which a material conforms to surrounding surfaces in order to relieve internal stesses, thus creating a seal.
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Unread postAuthor: chaos » Sun Feb 04, 2007 4:40 am

yer do the Teflon tape or get some loctite thread sealant it comes in a tube like toothpaste but a bit bigger

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Unread postAuthor: jrrdw » Sun Feb 04, 2007 7:20 am

I agree with Chaos, get the liquid thread sealant. Thread tape works, but has a tendacie(sp) to wade up when screwing two pieces together. Wire brushing the threads before doing any of this tends to make a better seal,
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Unread postAuthor: homeflake210 » Sun Feb 04, 2007 10:46 am

I would use both Teflon and pipe dope, that usually never fails.
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Unread postAuthor: frankrede » Sun Feb 04, 2007 2:25 pm

One or the other.
Theres no advantage to applying both.
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Unread postAuthor: homeflake210 » Sun Feb 04, 2007 4:18 pm

I use both cause its pretty much 100% guranteed not to leak.
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Unread postAuthor: Hotwired » Sun Feb 04, 2007 4:26 pm

Pull the teflon tape tight round the threads before screwing them in.

I've got about 6 different pressurised metal-metal screw thread connections on my cannon and none of them are leaking at 160psi.

It did however take several goes to fix all the leaks.
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Unread postAuthor: sjog » Sun Feb 04, 2007 5:34 pm

use both- thats what plumbers tell me
when wiping off excess dope it shines the copper/brass real nice.
works first try
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Unread postAuthor: UKSGC » Mon Feb 05, 2007 3:47 am

Im a plumber and I would tell you to use one or the other.

PTFE or plumbers tape works by melting (due to the friction and compresion created by forcing it into a very tight space) into the microscopic and not so microscopic gaps . The tape that wads up at the ends is whats been forced out cos it wasnt needed.
If you lubricate it it wont work as well.
JMHO
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Unread postAuthor: Legendpilot » Mon Feb 05, 2007 10:08 am

I'm unsure of the exact name, but I use a pink colored teflon tape I found at Lowe's. It's designed specifically for gas applications and is a little thicker, yet more plyable than the white teflon tape. JMTC -Lp
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Unread postAuthor: taterjim » Mon Feb 05, 2007 10:57 pm

I used some thick nasty looking pipe dope on my first pneumatic and it worked really well.
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Unread postAuthor: Velocity » Mon Feb 05, 2007 11:22 pm

There are two types of teflon pipe tape: one is intended for use in water lines and such, and the other is intended for use with gas.

The former is usually white and thin, while the latter is usually various colors and three times thicker than the former.

To get those threads to seal, take white teflon pipe tape, and wrap six layers right on the edge of the threads. Once this is done, wrap three layers on the portion of the threads right next to the ones which were just wrapped.

I almost never have pipe leaks when I use this method. If you use too little teflon pipe tape, it will obviously leak, for obvious reasons. Unbeknownst to many, using too much tape will also cause leaks. While excess tape will be pushed out of the threaded joint, too much excess can prevent the two pipes from being twisted together tighter, thus creating a threaded joint with leaks
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Unread postAuthor: maz oner » Tue Feb 06, 2007 4:57 am

ive got a thick white one and i only use oneand half layer and test it in the pool for bubbles and i almost always get a perfect seal
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