Sealing hard compressed air lines

Discussion in 'The Garage' started by Pro_Marinero, Mar 13, 2007.

  1. Pro_Marinero

    Pro_Marinero Carbon Sasquatch

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    I'm in the process of plumbing hard air lines in my garage/shop. Everything is plumbed and now I'm seeing bubbles while doing the soapy water test at a couple of fittings. Is there a way to seal this without taking everything apart... like Permatex Aviation sealant? I happen to have some and I know it's tough but I'm looking for a second opinion. Thanks.
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  2. KTM640Dakar

    KTM640Dakar Motorsick

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    Teflon tape.
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  3. Lone Rider

    Lone Rider Registered User

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    I thought it was a requirement....:D
    Better than dope....pipe dope, that is.
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  4. Pro_Marinero

    Pro_Marinero Carbon Sasquatch

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    I forgot to say I have teflon at all the fittings. Still having issues. Any good ideas beyond teflon?
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  5. Harrington

    Harrington Been here awhile

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    What kind of piping are you talking about?
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  6. Pro_Marinero

    Pro_Marinero Carbon Sasquatch

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    1/2" Galvanized
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  7. comes naturally

    comes naturally renewed hope

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    That's what I used...did you tighten it with a pipe wrench?
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  8. normsworld

    normsworld Adventurer

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    I work with gas pipe for a living , sounds like its steel threaded pipe .I use teflon pipe dope , the taper in threads SEAL the joint and the dope is more or less a lubricant, possibly compressing in a gap . Unless you wanna weld it , take it apart ,check the threads and tighten it good this time . I've seen copper type M , PEX and heard of cpvc used for 100 psi air . I'm gonna use pex when I do mine .Love the shit it is not Quest at all !
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  9. comes naturally

    comes naturally renewed hope

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    How much is leaking?
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  10. normsworld

    normsworld Adventurer

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    Just saw it's galvinized , don't weld it!
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  11. Harrington

    Harrington Been here awhile

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    I'm a plumber. You shouldn't be having air leaks if the threads are good and you are making them up correctly. A good rule for threaded pipe is the 3 turn rule. You should be able to make up a threaded joint 3 full turns by hand before a wrench is needed. You can make an improper thread seal but it's harder, especially with over 100psi air.

    Here's how I make up threaded joints. Start with good clean threads. I then put on a full swabs of teflon pipe dope. I then put on a few laps of telflon tape. It's important to put the tape on clockwise when you are looking at the end of the pipe. I then put more teflon dope over the tape. I use this method when I do most natural gas piping.

    With that being said, I'd rather install copper air piping. It's faster to install and it works just the same.

    DON'T USE PVC PIPING FOR AIR LINES---IT WILL EXPLODE UNDER PRESSURE IF HIT HARD ENOUGH---
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  12. katbeanz

    katbeanz earthbound misfit, I

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    You should be able to run threaded pipe into fittings halfway by hand, I've used teflon tape and rectorseal both on some stubborn stuff, tape first, then the pipe dope. On air lines if the threads are cut right, usually just rectorseal.
    Loctite also makes hydraulic sealant I've used successfully after others had tried, it's not coming apart without heat. :evil
    As far as compressed air, If I can't hear it, it's not a leak, unofficially. :D
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  13. Pro_Marinero

    Pro_Marinero Carbon Sasquatch

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    I followed the clockwise rule and thought I wrenched them on pretty good. Obviously not. :bluduh
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  14. hardybaker

    hardybaker Been here awhile

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    You did use tapered couplings didn't you? Somewhere, I have run across straight couplings that have caused me problems.
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  15. Pro_Marinero

    Pro_Marinero Carbon Sasquatch

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    Went back and did it right. Rectorseal and teflon tape all the way around and tightened 'er down good. I love doing a job twice. :doh
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  16. R_W

    R_W wannabe

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    In the past we have used post-install loctite (green??) with success on air lines. Shot brake cleaner in to clean the threads and made sure to let it cure before re-pressurizing.
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  17. katbeanz

    katbeanz earthbound misfit, I

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    Oooh, thats good to know, Thanks! :clap :thumb
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  18. Poolside

    Poolside Syndicated

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    <BR>NPT pipe threads, what a racket.

    The NPT thread profile has a clearance between the crests and roots of the threads, and forms a spiral leak path. The crest or the root the triangular thread profile (female or male) is slightly truncated.

    It was designed that way, and certified that way. Can you say Plumbers Union?

    The National Pipe Taper can be made to seal by mechanical deformation of the threads, if enough torque is applied. And that is how most of the pre-to-be-repaired, and later pre to-be-copper-repiped buildings were plumbed. Not only pressurized water supply lines, but drains and vents too.

    So the torque moves enough metal to make a sealing point. But that designed-in spiral path will be filled with water up to wherever the singular point in the spiral that enough metal was bulldozed into a sealing point. Ridiculous, but long-term profitable.

    Teflon tape merely increases the chances of a seal by more-often-than-not making a teflon 'plug' somewhere along the tiny 'truncated pyramid' spiral-shaped leak path.

    Pipe dope works by filling the spiral leak path, lubricating the metal deforming process, and being viscous enough so it won't be pushed out of the spiral leak path, ala toothpaste.

    With pipe dope, the spiral leak path can remain. But because the cross section of the path is so small, and the friction needed to push the pipe dope through the path is so high, an effective seal is formed. A seal made without metal-to-metal contact.

    - Jim<BR><BR>
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  19. Harrington

    Harrington Been here awhile

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    :rofl
    I bet you have 55 definitions of picking your nose too. I really like the part where you lay the engineering at the feet of the Plumber's union. I'm sure you don't have a hidden agenda there......:lol3
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  20. Poolside

    Poolside Syndicated

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    <BR>
    I don't know Harrington, I think I'm un-hiding an agenda. We are the only industrial nation that builds a leak path into its pressure piping. Look up the NPT thread profile specs.

    Course there's a new-ish thread profile called Dryseal. It's based on NPT but it's designed to seal.

    "The roots of both the external and internal threads are truncated slightly more than the crests, i.e. roots have wider flats than crest, so that metal-to-metal contact occurs at the crests and roots coincident with or prior to flank contact,"
    http://www.normas.com/ASME/pages/B1.20.3.html

    The designed-to-fail feature of NPT was paid for. I suppose if you paid me enough I'd design most anything.

    - Jim<BR><BR>
    #20