What makes compression fittings leak?

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by guy48065, Oct 6, 2013.

  1. guy48065

    guy48065 New Member

    Messages:
    111
    Location:
    SE and north MI
    I was pressure testing a repair I made on a faucet and got bubbles. Not from my solder, though. The 1/2MIP to 3/8" compression fitting was leaking at the crimp band AND the taped threads. All fittings are brand new, undamaged and had good clean threads. The ferrule was tightened until there was a visible "waist" on the 3/8 copper tube (new). Am I doing something wrong or:
    1 - should I dope up everything with paste as a mater of practice? or
    2 - will this be leak-free to water and only leaks thinner air?

    First picture shows the setup. 80psi is trapped in supply line and placed underwater.

    Second picture is taken underwater and shows the bubbles forming all over this wrench-tight fitting.

    [​IMG]

    [​IMG]
  2. DonL

    DonL Out of the Trades

    Messages:
    3,901
    Location:
    Houston, TX
    Probably because the No lead connections are to hard of a material to compress properly.

    And the Metric conversions are just enough off that a good seal is not possible unless you over tighten them.

    Just my guess.

    Tighten just till they break then back them off 1/4 turn, Then buy a good one.


    Looks like your setup is using a flare fitting ?


    Have Fun.
    Last edited: Oct 6, 2013
  3. Terry

    Terry Administrator Staff Member

    Messages:
    14,889
    Location:
    Bothell, Washington
    Are you sure that's even a tapered thread on the chrome adapter. May fittings like that for faucets are straight threads that are meant to pull up tight. Not snug up to a taper.
    Lav supplies and lav nuts are cut and threaded straight, without a taper.

    The compression side with sleeve; those I use some light oil and tighten up.
  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,888
    Location:
    New England
    If you use tape on an actual compression fitting's threads, THAT will cause it to leak! Tape or dope is only required on a tapered threaded plumbing fitting. Straight threaded connections rely on either compression or a gasket of some sort to make the seal, and the threads and nut are only to compress things together to create the seal (and thus, are not tapered and require no sealing material in them).
  5. dj2

    dj2 Member

    Messages:
    407
    Location:
    California
    If I face a situation like this, I immediately go to plan B: replace the compression with a male adopter.
  6. guy48065

    guy48065 New Member

    Messages:
    111
    Location:
    SE and north MI
    The chrome adapter was tagged 1/2"MIP - 3/8" compression. It's not a fitting that came with the faucet--it's part of the pressure test jig. When I'm ready to use the faucet I'll cut the copper tubes shorter and use a pair of braided 3/8 - 3/8 hoses to connect to the stop valves.

    The 1/2" tapered pipe end of the fitting has 2 layers of tape on it. I'm surprised it leaks--brass and plated brass normally have nice smooth threads with no voids. As for the compression band I suppose I could just keep cranking on it & see if it stops but that just shouldn't be necessary--the parts are new, clean and dry. Maybe a dab of oil or grease is a good idea, but I thought the crimp of the brass ferrule on the bare copper should be done dry to insure they fuse together.
  7. DonL

    DonL Out of the Trades

    Messages:
    3,901
    Location:
    Houston, TX
    May be the difference is made in USA and made in China. The pipe bottoms out before the threads are tight.

    If you do like Terry recommends , a little lube will let you get the compression tight without breaking it.


    Good Luck
  8. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,481
    Location:
    Cave Creek, Arizona
    What do you mean by a "waist" on the tubing? Once you deform the copper, it is almost impossible to NOT have a leak until you torque it even further. Chrome fittings may leak because the plating on the threads can cause an incompatibility.
  9. guy48065

    guy48065 New Member

    Messages:
    111
    Location:
    SE and north MI
    Yeah I was wondering about the chrome but that was the only type in stock. I never have issues with brass fittings.
    That's the point of my question--even something this simple has a right and a wrong way to do it and I may be doing it wrong. It's not like fittings come with instructions... :)
    The ferrule HAS to deform the copper or it won't fuse to it and seal without slipping. It can potentially leak between the ferrule and tube, between the ferrule and fitting seat, or between the ferrule and cap. That's a lot of surfaces on one connection. I'm assuming this is a fluke (since there are no "happens all the time" replies) but both supply lines leak at the same rate and since the fitting only comes with 1 ferrule & cap, the 2nd set came out of a bag of replacements that aren't even from the same mfr.

    Do the 3/8"OD fittings on hose (SS braided or reinforced vinyl) seal any better?
  10. guy48065

    guy48065 New Member

    Messages:
    111
    Location:
    SE and north MI
    I think I need to hit a different supply and find a solid, unplated, brass adapter.

    Or just drop it--I'm satisfied my solder isn't leaking.
  11. Terry

    Terry Administrator Staff Member

    Messages:
    14,889
    Location:
    Bothell, Washington
    [​IMG]

    I use a fitting like this. Though I guess that's going to change soon.
  12. guy48065

    guy48065 New Member

    Messages:
    111
    Location:
    SE and north MI
    ??
    Going all plastic & crimps?
    Brass is now a precious metal?
    My leaky fitting has persuaded you to give up on compression fittings?
  13. Terry

    Terry Administrator Staff Member

    Messages:
    14,889
    Location:
    Bothell, Washington
    We use compression fittings all day. No issues.
    Brass is bein phased out in 2014 because of lead on potable water.
    Once more reason so many faucets are coming with plastic supply lines.
  14. DonL

    DonL Out of the Trades

    Messages:
    3,901
    Location:
    Houston, TX

    That does suck. I think.

    There is nothing wrong with a compression fitting if installed properly.

    I will take lead over plastic any day. Plastic can make you sick also.


    Have Fun Everyone.
  15. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,481
    Location:
    Cave Creek, Arizona
    quote; The ferrule HAS to deform the copper or it won't fuse to it and seal without slipping.

    Incorrect. The edges of the ferrule press against the tubing to seal. IF they deformed the copper, it would be VERY difficult to "pull' the ferrules and the deformation would prevent new ones from sealing. Neither of which is the case in a proper compression joint. (In fact some will just slide off once the nut is loosened if it is type "L" or "K" tubing.) Tubing is very strong, UNTIL you deform it and then further deformation occurs very easily which is why you would have to tighten it VERY excessively to get it to seal.
  16. guy48065

    guy48065 New Member

    Messages:
    111
    Location:
    SE and north MI
    Well then I AM doing it wrong. I always thought ferrules were supposed to be crimped on so they can never move. Permanent. If I had to estimate the torque I typically use I would say maybe 10 foot-pounds on a 3/8 line.
  17. DonL

    DonL Out of the Trades

    Messages:
    3,901
    Location:
    Houston, TX
    Normally the ferrule will bite into the tubing, and if the connector needs replaced, you need a new ferrule and need to cut back to a new place on the tubing.

    The copper does get pinched, and the ferrule will not move on the tubing, after you tighten it then take it apart.


    Have Fun.
  18. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,888
    Location:
    New England
    The fitting doesn't need to be so tight it deforms the pipe to seal. You can make it tight enough to deform the pipe, and if you do, would need a puller (or cut it off) to remove it. Since that isn't uncommon is one reason why the tool exists. I haven't taken that many apart, but on those that I have, they weren't leaking, and I was able to pull the ferrule off without needing a tool. All that's required is intimate contact, not a depression or crimp effect.
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