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Old leaky 1/2" system - compatibility with metric parts

Discussion in 'Plumbing and Central Heating' started by dazzammm, 18 May 2012.

  1. dazzammm

    dazzammm

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    Hi,

    Wondering if anyone can help.

    Ive got an old 1/2" system but have a leak.

    One of my options is to fit a blank nut.

    Is it ok to fit a 15mm blank nut to a 1/2" joint?
     
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  3. Nige F

    Nige F

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    Yes - the sizes are close enough
     
  4. Charnwood

    Charnwood

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    If you mean put a blank capnut or cap on a 1/2" compression fitting, the threads are both 1/2" BSP, so yes it is OK.
    You will need to fit either a rubber or fibre washer in it.
     
  5. JimCrow

    JimCrow

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    not all the threads on old 1/2" compression fittings are the same "prestex" for example
     
  6. dazzammm

    dazzammm

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    hi, can you expand on what you mean by this.
    (the current nut has prestex on it and im not sure if this is a specification, manufacture or what.
     
  7. dazzammm

    dazzammm

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    wont this come with it?
     
  8. JimCrow

    JimCrow

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    The old half inch " Prestex" compression fittings had more threads per inch,

    finer threads than 1/2" BSP.
     
  9. Charnwood

    Charnwood

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    A rubber washer should come with a blank capnut, but a brass cap will not have one.
     
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  11. Charnwood

    Charnwood

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    Prestex is the brand name of compression fittings made by Pegler (now Pegler Yorkshire.

    If, as Jim says, their older fittings had a b'stard thread you will struggle to find a capnut to fit.

    You could try a blanking disk, but you'll only find them in 15mm.
    [​IMG]
     
  12. matt1e

    matt1e

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    A photo and a discription would be a help Daz
     
  13. dazzammm

    dazzammm

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    thanks.
    whats the difference between a blank nut and a blanking disc and why would you use one instead of the other?
     
  14. dazzammm

    dazzammm

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    would you expect there to be an olive with a prestex joint? I think my problem is there is no olive.

    and do i need a special prestex olive? if not what kind do i need?
     
  15. Charnwood

    Charnwood

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    Prestex is a brand of compression fittings made by Pegler.

    They used to do both Type A and type B joints, but now only do Type A.

    Type A:

    Type B, where the pipe is swaged or belled out:

    Blanking disc, as shown above, goes into a fitting, replacing the olive.
    Blank capnut replaces the olive and nut, and should come with a rubber washer.
    Blank capnut. This is conex's fig. 63b:
    [​IMG]
     
  16. dazzammm

    dazzammm

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    is it possible to put too much pfte tape on?

    ive wrapped it around the thread, where the pipe goes into the joint and about 5mm above that
     
  17. Charnwood

    Charnwood

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    Yes, it is, and "ive wrapped it around the thread, where the pipe goes into the joint and about 5mm above that" is.
    A bit round the olive should suffice, although no manufacturer I know recommends using PTFE on a compression joint.
     
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