MDPE pipe sizes...why?

[Mr Fizzion]

What's the reason for the diameters of MDPE pipe and why are they different to copper?

And another one: why is a street elbow called a street elbow? (The rather low quality article on wikipedia was of no help!

question: where is Doctor Evil? :-)

TIA

Mr F.

[Christian McArdle]

The pipe wall is much thicker. An MDPE pipe of the same diameter as a copper would have much lower flow. Also, as they aren't compatible with copper fittings, it is best not to have the same outside diameter, to prevent the temptation.

20mm MDPE is approximately equivalent to 15mm copper. 25mm MDPE is approximately equivalent to 22mm copper. 32mm MDPE is approximately equivalent to 28mm copper.

By "approximately equivalent to" is meant "slightly better than", especially for the 15mm20mm.

Christian.