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Discuss Half inch or 15mm pipe fittings question in the Plumbing Forum area at

  1. Marty1979

    Marty1979 Member

    Hi folks

    Need some help ASAP please. I cannot fully turn of the mains inside my property due to very old stop cock under kitchen sink.

    Property has two stop cocks internally (house is 1930's build) with the first being made of lead on one side of stop valve and copper coming out of the other side (this stop cock is hidden under floor boards) Then there's a 2nd internal stop cock under kitchen sink which won't turn off properly but needs replacing regardless.

    House is on communal stop tap in the street so would turn off five houses.

    I want to cut into the copper pipe between the two stop cocks but cannot tell whether its half inch or 15mm

    Question is:

    1) If it's 1/2 inch copper how can I tell?
    2) What would be the best method to connect to new 15mm copper - push fit or end feed solder?
    3) If end feed, do I need special end feed couplings or just use 15mm?

    Thanks very much all.

  2. steadyon

    steadyon Active Member

    1. 15mm pipe is almost exactly 15mm in diameter, 1/2" is a little larger in diameter. The best way to measure diameter is with a set of vernier calipers, but if you don't have these, then measure the circumference and divide by "pi" which is generally accepted as 3.14159. To measure the circumference wrap a strip of paper round the pipe with one edge in line. Cut the paper with a sharp knife (not cutting the copper), and measure the strip which was wrapped round the pipe. If it measures 47.1 mm the pipe is metric, if a bit more its 1/2"
    2. I'd always prefer a soldered connection. However, the pipe must be completely dry to solder it, and if you can't turn off the under floor stop valve, you'll have to turn off the one in the street. If you are confident with soldering, go for it, otherwise consider a compression fitting, provided it is in an accessible place.
    3. Not sure I understand the question. If you are replacing the above floor stop valve why not just turn the water off, undo the nuts on the above floor valve, remove it and replace it. Provided the old and new valves are the same length you shouldn't need to alter the pipe work.
    • Informative Informative x 1
  3. John Harwood

    John Harwood New Member

    I sympathise with your predicament... I learned about this the hard way when I didn't know much about what's available. You can't hammer a 15mm connector on to a 1/2" pipe and expect the solder to run, is the lesson you quickly learn. You can get adaptors for 15mm to half inch pipe, both in soldered and compression form. Why not just buy a couple so that you're prepared for the worst-case scenario? If you don't use them you can take them back for a refund in many retail outlets.
  4. scott_d

    scott_d Plumber GSR

    See if your water supplier will replace your lead main
  5. Ric2013

    Ric2013 Plumber

    Unless you are very confident, and if the water board won't do the work for you, then I'd suggest a plumber in to fit a new stop cock to the existing internal pipe. If you have to turn off five houses for half an hour, that'll have to be done. Give the neighbours warning and get the water board involved if they insist on being obstructive.

    Using the external stopcock to allow maintenance to the internal one is, I would suggest, its intended purpose.
  6. johnduffell

    johnduffell Member

    What a genius!! Complete accuracy give or take the paper thickness:D
    • Like Like x 1
  7. Marty1979

    Marty1979 Member

    Thanks very much mate. I'll go with the compression fitting if too wet. Will a 15mm compression coupler be okay to use on half inch pipe?
  8. Marty1979

    Marty1979 Member

    Thank you all for your replies. I am happy to fit the stop valve as have had plumbing experience however just wanted to know if it's OK to use a 15mm coupler on 1/2 inch pipe?

    I am also buying an end feed solder straight coupler which is 1/2 inch to 15mm just in case it is dry.
  9. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    You should be fine might need to use a bit of sand paper to take any paint / high spots off etc

    Try the olive first if that fits your golden
    • Agree Agree x 1
  10. Marty1979

    Marty1979 Member

    Thanks mate. I'll use a copper 15mm olive. So basically if the 15mm olive goes over the pipe it's all OK yeah? Should I use PTFE around the olive as belt and braces?
  11. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    No you can use some jointing compound if you want to

    And correct

    Now depending on how cheap your fittings are you might need to use a round file on the nut
  12. Marty1979

    Marty1979 Member

    OK mate thanks again. What brand should I buy so that I don't have to file down?
  13. Best

    Best Trusted Plumber

    Buy a conex brass connector. Expensive, but worth it.
    They are good quality and the body of the fitting is a slacker fit on the pipe, so very suitable for the 1/2” pipe, plus the brass conex nuts are slack on pipe, unlike the nasty standard cheap fittings
    • Like Like x 1
  14. Marty1979

    Marty1979 Member

    Bless ya mate and thanks very much. Learning all time!
    • Like Like x 1
  15. Best

    Best Trusted Plumber

    No problem at all Marty. Use a smear of paste around the olive of any compression joints. V2 Lube is very good, but expensive
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