Leaking mdpe pipe at compression fitting

[sastek]

Hi, I need some advice about a leak. I recently had a leak from the underground stop cock for mains water, so replaced it with a new one. The problem I have now is that the mdpe pipe is quite loose at the compression tee, I can't get the nut to tight enough for the olive to clamp properly on the pipe. The pipe does have a insert, I've tried using a new olive and a used one that was in good condition. I'm wondering if it has something to do with the diameter of old black pipe vs new blue pipe.

 

[muggles]

Almost certainly different diameters. I'd take the tee out and replace it with a Philmac one

 

[Deleted member 267285]

Iirc black pipe is 3/4”/21mm?

 

[sastek]

The new blue pipe is 25mm, I'm wondering if the old black pipes are 1 inch

 

[polesapart]

Some info here

https://www.stevensonplumbing.co.uk/black-alkathene-pipe-fittings.html

 

[oph]

Alkathene which is old hat from the 70s and mdpe on the right.

Probably needs a transitional coupling to get from either material, not the tap.

 

[JohnD]

I have black alkathene incoming, and the main stopcock ( a brass one) is alkathene ?one inch? incoming and copper outgoing, quite a common size. I think your bit of blue pipe is the source of your trouble.

 

[sastek]

Thanks for the responses, they were really helpful.

So the new blue pipe is the wrong diameter, luckily I've found a bit of old black pipe to replace it with. I also think that the stopcock is the wrong size, it's for 25mm pipe. The manufacturer makes adaptors, so hopefully they work with this stopcock.

 

[JimCrow]

The stopcock you have ( Philmac 3G 2833) does both 3/4" Alkathene and 25mm MDPE pipe, no need for adaptors, use the original pipe you cut out with the olive from the brass compression tee to the stopcock.

 

[sastek]

Well spotted Jim, thanks! For some reason I recalled it was a Plasson one.