Compression Joints

Discussion in 'Plumbers' Talk' started by AdamJames, Apr 5, 2019.

  1. AdamJames

    AdamJames New Member

    Hello,

    Quick question about compression joints. I did a few of these years ago when we moved into our house, all are still fine. But need to replace a washing machine valve, so was refreshing myself on compression joints by looking on the internet.

    It seems that most people recommend using PTFE tape and/or "grease" (not sure of the right word for the stuff). But I never used anything before and they have never leaked. So is it really necessary?

    Actually it's got me very confused and I've lost confidence in doing it myself now. Must be age!

    So what gives? Do I need PTFE and "grease", or can i get away without it?

    Thanks,

    Adam
     
  2. Heat likes this.
  3. LEH

    LEH Active Member

    This always seems to set off a lot of arguments.

    I'm not a plumber. What I do, provided it's somewhere accessible (which I would always want a compression joint to be). Do it up, don't over tighten. If it weeps, keep nipping it up bit by bit until it stops. If it's still not having it, take it off, bit of jointing compound or PTFE on the olive, reassemble.

    In principle shouldn't need jointing etc, but I guess the quality of these things varies. My plumber always uses jointing compound - I guess because it's insurance, you do it up, you can walk away without worrying about it weeping, no callbacks.
     
    Heat likes this.
  4. candoabitofmoststuff

    candoabitofmoststuff Screwfix Select

    In essence...

    A compression joint seals by having the olive "grip" on both it's inside and outside... The inside of the olive grips the pipe, and the outside of the olive is "pushed" against the fitting and the nut. The seal is made by the compression/deformation of the olive against the corresponding bits, the pipe and the fitting, (the the deformation is only slight)

    Using PTFE tape around the olive is basically introducing a barrier to that seal. Using something else more "fluid", such as Fernox FSX, (which is like silicon sealer designed for compression joints), can help. It doesn't impede the compression joint, but can act as a "micro filler" meaning the olive doesn't have to compresses quite as much, and doesn't need tightening as might, (though it still needs to be tight). If all part are clean however, just dry is fine for a compression joint.

    On a taper thread joint, where there is no olive, and the seal is made by the thread tightening up on the taper, is where PTFE should be used. The tape does act as an actual sealer in this instance, because the surfaces of the threads aren't precision enough to create a good seal.

    At least, speaking as a DIYer, that's my understanding... and it's always worked for me.

    Good luck,

    Regards,

    Cando
     
    Heat, chippie244 and seneca like this.
  5. gas monkey

    gas monkey Well-Known Member

    you should set an olive in a fitting designed for it torque it up to the correct setting for the material size etc then remove and fit it in the fitting
    no one dose
    put in through nut and olive tighten up a bit open up if leaks tighten up bit more or
    ptfe olive or
    plummers mate the olive
    or both
    or change the olive for a soft one if using old fittings soft one being a copper not a brass one
    if overtighten the nut will split but you prob want see it until it leaks
     
  6. Plumbers Mait is for Sanitary Ware not compression fittings, PTFE screams of a diy job and not something a time served Plumber would do on a new fitting.
     
  7. gas monkey

    gas monkey Well-Known Member

    Know what you mean dog giving the full picture
    As for full time plumber no one has mentioned how to put a fitting on correctly
    And no one has said the correct thing is to re new it so tell everyone
    Not only a plumber but sparky and gas fitter roofer fitted windows doors you name
     
  8. Wayners

    Wayners Screwfix Select

    I put tiny dab of vasiline on the thread. Tiny bit.. So easy to do up and judge the force vs dry and it grinds and binds.. No PTFE tape... On a side note.. The more people you ask the more different options you will get so I guess its whatever works for you.. Over tightening as that is the biggest problem imo. Just a gentle nip up and make sure pipe is clean
     
  9. Astramax

    Astramax Super Member

    When I was training 45 years ago on day release plus one evening every week for 4 years it was instructed: Make sure every mating part is clean then do it up finger tight plus half a turn with a spanner to nip it up.
     
    kiaora likes this.
  10. gas monkey

    gas monkey Well-Known Member

    agree and that will give the correct torque for that type of fitting others will be different s/s is a turn and a qurter and all should be set in a former and tested with a torque spanner but as you know they never are
     
    Heat likes this.
  11. kiaora

    kiaora Guest

    Hi
    I’ve actually retired now, but I’m still involved in my company, we use press fittings now .

    It’s more economical would you believe !

    Because we work in schools and public buildings, not using flames or hot work, the insurance is a lot less than the cost of fittings.
    And as you all know, trying to solder a pipe with a bit of water in it is a pain !
    So, with the press fitting, is a lot quicker.
    Regards
    Peter
     
    WillyEckerslike likes this.
  12. Wayners

    Wayners Screwfix Select

    How many plumbers carry a pump and remove water from pipe? Only ever seen one use a pump and I thought brilliant... Was a pump that is used with oil change on car instead of removing sump plug. Cheap enough and worked a treat removing water from pipe


    [​IMG]
     
    Heat likes this.
  13. Heat

    Heat Screwfix Select

    Some brass compression fittings and olives vary.
    The threads can be a bit tight, or slightly flawed and ‘feel’ as if joint is compressed.
    Some olives are very heavy metal, or a harder type of metal and hard olives can be near impossible to compress.
    Personally I would say each type of fitting can require different force to compress the olive and it is best done using paste as a fine sealant and helps lubricate the joint.
    Also I prefer to undo the joint to check olive is compressed and full on.
     
  14. Pollowick

    Pollowick Screwfix Select

    They certainly do, expecially comparing brass and copper olives. Ease of compression is the main reason copper olives are specified when using compression fittings of plastic.
     
  15. Heat

    Heat Screwfix Select

    Yes, the soft copper olives mould to the soft plastic pipes.
    Although quality brass olives are better on metal pipes on heating systems as heat won’t cause movement and risk of slight weeps through time
     
  16. Astramax

    Astramax Super Member

    Yes I agree fittings have always have varied, teaching technique was as a rule of thumb, experience and knowledge follows later.;)
     
    Heat likes this.

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