water pipes - size advice

[stev]

Hi all,

There's a small pipe running fresh spring water into a tub for animals to drink from, it runs under a summer house im trying to renovate. Pipe is 25mm in diameter, but internally is only about 16mm diameter.

I'd like the water to do different things before heading into the tub, including filling a small pond, and also providing a tap in the summer house for as and when needed. So im asking what pipe size to use (and go and buy) which will work outside and in, and be compatible with lots of fittings. I ask because I've struggled to find anything that will fit current pipe.

I've bought a y splitter, which has 25mm and 20mm fittings, and I've also got some reducers that fit into current pipe and on the other side go to 19mm. Is 20mm internal diameter quite common?

Hole I've made sense, just don't want to go ahead with incompatible pipe sizes!

 

[stev]

I should say I'm thinking about this: http://www.diy.com/departments/polypipe-mdpe-pipe-dia25mm-l25m/184651_BQ.prd

Apparently it has an internal diameter of 20.4mm so hopefully would fit over the Y splitter (which is 20mm). Anybody recommend MDPE for this sort of thing?

 

[b3taman]

Hi stev
You don't say what the existing pipe is made of. Is it metal or plastic? If it's a plastic pipe similar to the MDPE pipe you posted a picture of, then it might be old pipe which was made in Imperial sizes also, which is why you can't match it up.
If you can get something to fit the old pipe securely, then by all means use the 25mm (external size) MDPE pipe which is an industry standard and used all over the place. Sounds ideal for what you are trying to do. The fittings for this are widely available - try Screwfix. Often the terminal fittings e.g. a hose bib tap, are fitted using an MDPE to screw thread adaptor - e.g 25mm MDPE to 1/2 inch or 3/4 inch male or female. Again these adaptors are widely available. Just remember to use about 12 turns of PTFE tape on the male thread to get a good seal when you tighten up. Hope this helps.