Replacing water stop cock/valve - technical question

[Terrapin]

My mains water supply (bungalow, concrete floors) enters the house through the bathroom floor. The bungalow is 1960's and the main appears to be the old 1/2" copper covered in denso tape where it rises from the concrete. The isolation valve is old/stiff and does not shut off completely so I want to replace in the near future. I suspect the copper pipe is a thick walled type.
Questions:
I think you need a special compression fitting for soft thick wall copper - I do not think you can simply use a standard olive etc. ?
How do I go from the old 1/2" pipe to a new 15mm stop valve?

All advice welcome - thanks

 

[tonybhoy]

Pipe will be the same size as 15mm. Yours will be 1/2" but there is no difference only the odd sizes are different ie 3/4" ,inch and a quarter ,inch and a half and so on.

Having said that are you sure yours is 1/2"? Might well be 3/4" in which case you can buy an imperial olive and use 22MM couplings.

Personally I wouldn't bother changing the valve ,either cut a new one in above the old one or buy yourself a 'toby key' for about £15 and then you can turn the water off from outside on the pavement if the toby valve cover isn't covered over that is