MDPE water pipe 25mm or 32mm?

[Ian Phillips]

Hi, after some advice on which size of MDPE water pipe is best to install?

 

I have a run of about 45m from the existing meter to the new house position. I have been advised that 25mm should be fine but 32mm would be better! The water meter has a 25mm outlet on it which cant be changed to 32mm without changing the whole meter. Now if I run a small section of 25mm pipe from the meter and then add a joint to up it to 32mm then continue in 32mm pipe will this still work with regards to the pressure/flow?

Surely having the bottle neck at the meter will mean no increase in pressure or flow? Anyone know more about such things?

 

Thanks

[Oz07]

I had 25 similar distance was fine. Having 32mm in new place on 10m run because pressure seems crap locally and wanted good flow rate 

[JFDIY]

The losses in a 25mm pipe are proportional to the length, so a 32mm pipe will flow more even with a few meters of 25mm at the start.

 

I fitted a 32mm supply for my place (a 40m run if memory serves) the water authority would only use a 25mm tapping off the main and a pre-piped 25mm meter box, it was then stepped up to my side of things and I felt it was all in vain, especially as the fittings within your property become large and bulky with 32mm.

 

That said it only cost about £30 more and I'd probably do the same again.

[Neil]

I am approx 100 metres from the main supply and was advised to use 32mm. The flow and pressure are both very good. You would need a 32mm stop tap in the property, but everything else would be stepped down to 22 or 15mm to supply the various outlets.

[Ian Phillips]

Thanks for all the replies, looks like I will be taking back some of the fittings and pipe and replacing them with 32mm! I have already put in some 25mm pipe but that is all overground and temporary for the caravan and workers toilet etc so this can stay in place.

 

[Oz07]

what did you all do for stop taps? I've gone 32mm to 28mm convertor, 28mm stopgap then will probably step down to 22mm to feed a manifold

[Oz07]

also i've been quoted based on 32mm connection which I think incorporates a larger meter feed. iirc someone on this forum had a 32mm feed connected with a smaller meter on the boundary, had photo evidence and got a substantial discount after the works had finished

[Neil]

I went with a 32mm stop tap in MDPE then reduced down to 28mm and into a pressure gauge / regulator. Then reduced down to 22mm before heading off to kitchen, hot water cylinder, bathroom etc.

[Oz07]

Do you think pressure regulator nessecary?

[JFDIY]

Mine comes in as 32mm mdpe, then to a 28mm compression into which goes a 28mm/22mm fitting reducer followed by a short section of copper to a brass stop-tap, then a Tee to take an un-regulated feed to garden tap, where you might want the full mains pressure. 

 

The house run is 22mm into a 3bar regulator, similar to @Neil above, then splits for cold and unvented cylinder.

 

I was wary of using plastic stop-tap, which based on @AnonymousBosch's experience seems to have been a wise choice, also insist on an isolation point outside the property for the same reason

 

if you're going to have an unvented cylinder then it will most likely come with a regulator which you put before the cylinder to keep both hot and cold at the same pressure, this is for two reasons, to protect the cylinder from running at too high a pressure but also so if you have mixer taps there isn't a higher pressure at the cold trying to back-feed the cylinder and again over pressurising it.

 

Oh and don't forget the drain cock, which I think I've recently boxed into the wall - doh!

 

 

Edited January 13, 2020 by JFDIY

[Conor]

There's pretty much no disadvantage to using 32mm over 25mm. 

 

Simply put, the larger the pipe diameter, the lower the fluid velocity, the lower the friction/turbulence between the fluid and pipe wall and therefore lower pressure loss.

 

The fact that there will only be a 20 or 25mm pipe from the main to the boundary box isn't a huge issue, as it will be a short length and pressure drop will be low. Obviously, having 32mm from tapping to tap is best, but unless you're filling a swimming pool, won't be an issue.

 

Easier way to step down diameters is to bring the 32mm pipe in to the house, reduce down to 25mm PE, fit a 25mm stop tap, then taper down to 22mm copper or PEX. 

[Temp]

5 hours ago, Oz07 said:

Do you think pressure regulator nessecary?

 

Not unless the pressure is very high.

 

Should really do a static pressure and flow rate test before deciding what sort of plumbing and heating system to install - just in case its too low for a mains pressure system.

[Ian Phillips]

Thanks for all the replies, I have decided to go for the 32mm size.

[Onoff]

I ran my new (25mm) supply in it's own duct. Might make replacing it easy if ever required.

 

 

The old pipe wasn't well...