I'm doing a major house renovation & have got to the stage where I need to move the incoming water pipe. I've exposed the pipe in question which is black plastic, I can't measure the diameter without cutting it open which I don't want to do until I can reconnect it all back up. I've measured (as best I can) the external circumference of it which is 68mm . Using a converter that would mean the pipe is 21.6mm diameter. The metric choice is 20mm or 25mm, imperial would be 1/2" which is 21.4mm so I'm guessing I have an imperial plastic water main? (house built in '79 ~ '80 era) Using the same converter it says a 20mm pipe would have a circumference of 62.8mm, there is no way my measurement is that far out! So, If I'm right how do I join an imperial 1/2" plastic pipe to a metric 20mm? I couldn't see anything on the Screwfix site for that Thanks
Done some more digging & found this..... "One point to bear in mind in the UK is that the measurement quoted for imperial sized pipe is the INNER diameter of the pipe whilst the measurement for metric pipes is the OUTER diameter" Which changes things a little! Now I'm REALLY stuck! The imperial choice then would be 3/4" I guess, that gives a metric diameter of 19.5 (internal), I'm guessing the external to be 2mm bigger so 21.5mm, that gives a circumference of 67.5mm, half a mm less than my measurement which is pretty close. So, If I am now right how do you connect a 3/4" plastic pipe to a 20mm?
Ok thanks. I've taken another loo at it & I think I will try reusing the existing stop cock so I know all I need is 15mm pipe. I've got to get it sorted as they are laying a floor tomorrow!
If its black then its imperial if it blue then its metric. you can get conversion inserts to get over any problems speak to your local plumbers merchant they should be able assist you and get you the correct bits you need
When looking around I can buy black in metric so it doesn't seem as simple as that! Do Screwfix sell the conversion inserts?
you have what is known as 1/2 black alkathene, although its 21mm external the internal is 1/2, here's an old trick we owd plumbers use, use a peice of 15mm copper pipe as an insert,
I don't know about a 20mm stopcock, i've never tried that, but i've used 22mm fittings on it with 3/4 olives and thata been ok,
On a side note I guess new builds would be 25 or 32mm? If I lay a new pipe would the water company be happy to connect that up when I get a water meter fitted? Or do you really not need anything larger than what I have now? Thanks again
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