Going from 32mm MDPE to 22mm copper

[jamiehamy]

Hi all, 

 

I think I may be being a bit thick, but our incoming supply is 32mm, which I'm going to run right up to the plant room and tee off to the UVC and to the cold water manifold and fit a reducer to each. Both are 22mm copper pipes - how does one reduce down from 32mm MDPE to 22mm copper?! I can't find the right reducers but reckon I'm missing something really silly. 

 

Thanks!

 

J

[Nickfromwales]

This

or one of these and reduce to 22mm from 28mm through this with one of these in the outlet instead of the 28mm olive.  

 

[TerryE]

@jamiehamy was there a reason for using a 32 mm MDPE supply instead of 25mm?  Broadly the 25 MDPE pipe has the same internal diameter as 22 copper, and 32 MDPE as 28 copper.  You aren't really supposed to expose MDPE to direct sunlight, so you'd normally go from MDPE to copper on entering the house. 

 

So another option would be to use a 32 MDPE to 28mm (copper) stop cock where the MDPE enters the house and then run your main riser backbone in copper and T the 22mm pipes directly off that.  If you are a bit wary of working in 28mm copper then you can always use the Pegler Tectite fittings which look neat and are demountable if you need to do so. 

 

@Nickfromwales, any comments?

[jamiehamy]

@TerryE - When the plumber (that was too expensive) was on site, he had a look at the incoming 32mm and said he'd just run that right up to the plant room - seems logical to me as it helps with a greater flow rate if I run 32mm as close to the inlets as possible?

 

None of the blue MDPE would be exposed to sunlight - it will run through the service void downstairs and up through the posijoists (there is a cupboard in the right palce that will allow a suitable bend rather than elbow) and pop up near the UVC/manifolds. It would be one unbroken run from the stop cock at entry to the above floor T to the UVC and Cold supply. 

 

I've kind of got a bee in my bonnet now (thanks to you guys :p)  about doing what I can to reduce pressure/flow variations when multiple outlets are open - it's one real bugbear in my current wee flat - the minute one thing comes on (like the washing machine), the hot water taps or shower immediately drop in pressure. 

 

[Jeremy Harris]

What size pipe you use really comes down to the incoming pressure.  Our rising main and stopcock in our old house is 15mm, and we have mains pressure hot and cold systems fed from it.  We never see any noticeable changes in flow with things like the washing machine coming on, or a toilet flushing, but that's down to the pressure coming in never being lower than about 6 bar.  The main downside with having a 15mm cold main going up into the loft and right down to the other end of the house from where it comes in is that it's a bit noisy.

 

For those with an incoming mains pressure that's right at the lower limit of a supply, then there's a great deal of sense in running the biggest pipes you can, as every tiny pressure drop removed helps.

[TerryE]

The other thing is as Jeremy says the noise  Over 1m/s and its audible.  The sound will start to carry at 1½m/2 and by 2, you are starting to get cavitation in the pipes which will literally wear them out: those vacuum bubbles imploding on fittings and pipe walls will systematically erode them.

[jamiehamy]

So - given that I have a 32mm incoming anyway (and very good pressure), should I run 32mm or go down to 28mm? If noise issue materialise, then presumably I can do something to reduce the flow to the supply anyway? Or is it probably six and half a dozen?

 

Cost wise the difference is negligible - was planning getting the pipe in the morning and running it through tomorrow whilst the replacement window is being fitted. 

[Nickfromwales]

28mm copper will be as good as it gets, for a domestic property. 

Can I assume you've read here and on EB about taking the outside tap off either outside as a tee off the 32mm mains incomer, or immediately after the stopcock eg before the PRedV?

Fwiw, if you can pull 32mm mdpe all the way in, in one shot, then I'd 100% go for it. Cheap and quick. 

I do flats that way. One common riser for gas and water and mdpe all the way into each of the flats. Saves a good few £'s, less joints and less noise. .