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Sealing threaded fittings

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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Sealing threaded fittings

Unread postAuthor: SEAKING9006 » Wed Mar 11, 2009 1:18 pm

I'm working on my 3rd gun this week, came across a new issue, since my first guns use the same slip/slip valve. How should one seal PVC threads safely? I got thread sealant but plastic isn't listed on the materials list on the can. Should I use my solvents, or twist tight and cover in mighty putty?


I ask because I don't have time to search using EDGE speeds and it's a new issue I haven't seen yet.
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Unread postAuthor: john bunsenburner » Wed Mar 11, 2009 1:30 pm

try teflon tape
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Unread postAuthor: jonnyboy » Wed Mar 11, 2009 1:56 pm

Teflon tape works well as do plastic bags, at home depot I have seen putty that you put on threads.
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Unread postAuthor: jrrdw » Wed Mar 11, 2009 2:07 pm

Any kind of thread locker is going to make it impossible to unscrew. Do youself a favor use teflon tape like mentioned above.
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Unread postAuthor: jeepkahn » Wed Mar 11, 2009 2:36 pm

also there is a paste called slic-tite that is rated to 3000psi w.o.g. and help ease disassembly if it's ever needed...
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Unread postAuthor: john bunsenburner » Wed Mar 11, 2009 2:45 pm

teflon is cheep and available and it si the best thing by far, so jsut stick to it.
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Unread postAuthor: SEAKING9006 » Wed Mar 11, 2009 4:07 pm

Cool, I thought it would be teflon tape. Though I wasn't sure if it was safe for PVC. I'm going to assume I have to layer it a bit thick...


The cannon (a bolt action 1in rifle) will be worked on this week and over spring break. I could simply attach the tank and stick a vertical grip with a button, but I'm gonna spend all week working on the little asthetics, like a foregrip and a nice pistol grip. That mighty putty is gonna see a ton of use on this thing. Not sure when I'll be able to post it, access to my PC for leisure is quite limited right now after a piece of Russian rougeware put my sis' computer into a botnet by dual-booting a stripped down linux kernel as a spambot and we had to strip the drive. I'm typing this on my trusty 8820 as I ride in my mom's van, on my brand new dataplan.
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Unread postAuthor: jimmy101 » Wed Mar 11, 2009 4:18 pm

SEAKING9006 wrote:Cool, I thought it would be teflon tape. Though I wasn't sure if it was safe for PVC. I'm going to assume I have to layer it a bit thick...

Nope, a layer or two is generaly adequate.

Note that the tape has little to do with the strength of the coupling.
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Unread postAuthor: psycix » Thu Mar 12, 2009 9:25 pm

Two layers? I always use 5 (though I am using metal fittings and higher pressures)
Many people claiming to have sealing problems just didnt apply enough of it.
Also make sure to turn it the right way, so it doesnt get messed up as you screw it in.
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Unread postAuthor: pharmboy » Thu Mar 12, 2009 9:33 pm

Also, there is a yellow thread-seal tape that's intended for use on gas lines. I believe it's thicker and a bit 'stickier' than the white teflon tape, which has no adhesive value, it just acts as a filler in the gaps between the male and female threads.
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Unread postAuthor: psycix » Thu Mar 12, 2009 9:53 pm

Actually, teflon tape is not a sealer or filler. Its a lubricator, allowing you to thread it in way further with less force. On loose threads, it may indeed also serve as a filler, but it is not the main function.
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Unread postAuthor: D_Hall » Thu Mar 12, 2009 10:22 pm

A general note on pipe threads.... There are two standards out there. NPT and NPTF.

Most folks are familiar with NPT (what you'll see with most "normal" stuff at the hardware). To the naked eye, the two are identical and you can in fact screw NPT stuff into NPTF stuff (and visa versa). The difference is *primarily* in the manufacturing tolerances which yields an interesting result...

NPT - by design - requires a thread sealant of some sort. True, it can sometimes be made to seal without a sealant, but that's just dumb luck; not design. So with NPT you'll need SOMETHING. Teflon tape is by far the most popular choice but as most folks are aware, other things will work as well.

NPTF - by design - requires no thread sealant. The tolerances are simply tight enough that the metal on metal contact is all that is required (properly torqued, of course).

Obviously, NPTF is more expensive (tighter tolerances are harder to manufacture). As such, it is generally only used for high pressure applications (where a sealant just won't hold up to the pressures).
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Unread postAuthor: sgort87 » Fri Mar 13, 2009 12:37 am

psycix wrote:Actually, teflon tape is not a sealer or filler. Its a lubricator, allowing you to thread it in way further with less force. On loose threads, it may indeed also serve as a filler, but it is not the main function.


Actually, no. It's meant to be used as a sealant, but also lubricates well.
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Unread postAuthor: SEAKING9006 » Fri Mar 13, 2009 11:30 am

This is the fiftieth time we've had this discussion, fellas. Teflon by nature is a solid state lubricant. In tape form, it seals well. It's lubrication proporties are just a beneficial coincidence in addition to it's ability to seal pipe threads.
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Unread postAuthor: jrrdw » Fri Mar 13, 2009 12:43 pm

SEAKING9006 wrote:This is the fiftieth time we've had this discussion, fellas. Teflon by nature is a solid state lubricant. In tape form, it seals well. It's lubrication proporties are just a beneficial coincidence in addition to it's ability to seal pipe threads.


So you wasn't sure if the thread sealent you had on hand could be saftly used and didn't want to get teflon tape? Knowing that you could use teflon tape?

What is the sealent you have on hand called, just so we know?
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