25 or 32mm MDPE

[Karmann]

Hi, we are having our driveway replaced and want to take the opportunity to replace the underground water supply pipe with MDPE at the same time. The pipe runs under our drive and then branches off to supply 3 other houses (so supplying 4nr 3 bedroom houses total). The current pipe is c27mm OD steel/iron.
I would like to use 32mm MDPE pipe to help future proof things a little as I believe my neighbours all have water tanks and gravity fed systems at present (I am off mains pressure). My question is whether using the larger 32mm pipe would have any down sides (apart from cost) or negative effects regarding flow or pressure (struggling to get my head around the physics of it all)
many thanks in advance

 

[ShaunCorbs]

Can’t you run 4 x 25mm eg each has there own supply ?

 

[exedon2]

The cost element is hardly worth thinking about (approx £10 on a 25 mts)
Good suggestion from Shaun to run separate supplies. Do you know the size of the mains tapping?

 

[EvilDrPorkChop]

Doesn't he mean put a new supply him to the road for himself and leave the others as? Like the old lead mains on terrace housing.

 

[Karmann]

The pipe tee’s off to the neighbours along the front of my house so would be using the 32mm MDPE to my house and also from the tee to the boundary with my neighbours where it would connect to the existing steel/iron pipe to their houses. Everything from there onwards is the other 3 houses responsibility. Sadly can’t run 4 separate supplies.

 

[ShaunCorbs]

I would cap of your supply to the shared main and run a new supply to your property then 25mm should be good enough aslong as the flow rate is there if it’s above 30lpm you could opt to a 32mm but the water board don’t normally tapp off the main in this (25mm)

 

[WC1]

There aren't any downsides. Imo always go bigger if possible. Laying 32 can be a lot harder work but that's probably not your problem. The water board should let you have 32 if you're supplying several properties.

 

[Karmann]

Many thanks for the replies. I think I may as well opt for the 32mm if there are no downsides as 25mm seems very small to supply 4 houses and I guess the internal diameter of 25mm MDPE may well be smaller than the existing steel/iron pipe due to wall thickness. I do understand that the tapp off the main could only be 25mm but my thinking is that if everything on my land is 32mm then at least my part is fairly futureproof if any of the other properties change to mains pressure systems in the future which could potentially cause pressure/flow problems with the smaller 25mm pipe.

 

[WC1]

If you're tapping is 25 there's not much point laying 32 because the restriction at the tapping will choke it all down. The id of a pipe run is really only as big as it's smallest id - a bit like the weakest link in a chain. Speak to the water board let them know it's for multiple properties.

 

[exedon2]

I would personally go with the 32mm if nothing else help reduce any possible frictional losses.

 

[Ric2013]

If you're tapping is 25 there's not much point laying 32 because the restriction at the tapping will choke it all down. The id of a pipe run is really only as big as it's smallest id - a bit like the weakest link in a chain. Speak to the water board let them know it's for multiple properties.

True to a degree (although a 25 tapping with 32mm pipe is still far less restrictive than the whole lot being run in 25), but surely 32 has the advantage that, if the water board ever decides to replace that tapping (perhaps if it is replacing the water main), the 32 is future proofed already?

 

[Karmann]

Thanks Ric2013, that was what I was getting at (but probably didn’t explain very well). I’ve now ordered 32mm so hopefully all good but than you all for your replies and advice. Much appreciated.