In article ,
writes
I want to use metal compression fittings rather than the standard push-fit MDPE
couplings on 20mm (I/D) blue MDPE pipe.

Can I use what is described as standard 22mm compression fittings where 22mm
presumably is the O/D?

Incidentally, I have a brass stopcock for use with 20mm ploy pipe and it has 20
cast into the side of it -suggesting that 20mm MDPE might require a special type
of compression fitting.

Can someone help clarify please?

Apologies for various bits of misinformation and confusion in this
thread, I think both myself and Andrew failed to notice that you said
20mm _I/D_ as the size for your pipe rather than _O/D_ (outside
diameter) which is the dimension that current domestic MDPE pipe is sold
and specified in.

If your pipe really is MDPE (is it blue?[1]) and has an I/D of 20mm then
it is actually 25mm MDPE pipe. This will not fit a 22mm compression
fitting as it is sized for the outside diameter of the pipe it is to
mate with ie either 22mm (_O/D_) copper or internal plastic plumbing
pipe, and sadly 25 into 22 will not go.

The conversion olive that Andrew pointed to was for adapting 20mm MDPE
pipe (_O/D_) to a 22mm brass compression fitting so that will not work
on the 25mm MDPE pipe that you have.

I note that the same outfit also sell a conversion olive for 25mm MDPE:

http://www.stevensonplumbing.co.uk/25mm-mdpe-olive.html

which I imagine will be for the next available size of compression
fitting which is 28mm (for 28mm o/d copper).

This means you need a 28mm compression fitting. If you then want to mate
22mm copper to this then you will need a 22mm 'reducing set':

http://www.stevensonplumbing.co.uk/c...set-28-22.html

or for 15mm copper a 15mm reducing set:

http://www.stevensonplumbing.co.uk/c...set-28-15.html


Finally and at last, I hope that helps (although I'm guessing you've
already been to a plumbers' merchant and got the bits you need), good
luck on your job.

[1] blue specified for underground service but also avail in black.
--
fred
it's a ba-na-na . . . .