Mdpe water pipe size

[thomp1983]

Hi all,

My current water pipe into my house is 20mm black plastic. I'll be rerouting it tomorrow around my new extension into the new kitchen, roughly 20m, Is it worth replacing it with 25 or 32mm pipe?

I can't replace the first meter from the stop cock on the pavement so whatever pipe I use will have to be fitted with a connector onto the existing 20mm.

Water pressure into the house isn't great, will a bigger diameter pipe improve this?

Thanks
Chris

 

[noseall]

My current water pipe into my house is 20mm black plastic. I'll be rerouting it tomorrow around my new extension into the new kitchen, roughly 20m, Is it worth replacing it with 25 or 32mm pipe?

Not if it is coming through something narrower prior to hitting the 25/32mm, no.

 

[thomp1983]

Ok, so once the new 20mm pipe is in is there anything that can be done to improve the water pressure?

 

[Exedon]

Ring your water supplier if your completely replacing your service they may well agree to change the section from the stop tap to the curtilage. Certainly the areas I work in the supplier would do this.
In truth black alkathene is not great as a water service.
Increasing the size won't affect pressure but could well increase volume due to being less restrictive.

 

[John D v2.0]

Pressure loss increases based on the length of the pipe amongst other things (flow rate also), so having a short length of 20mm followed by a long length of 32mm would be a lot better than a long length of 20mm.

 

[JohnD]

Not if it is coming through something narrower prior to hitting the 25/32mm, no.

That's widely thought, but I added a 25mm plastic pipe to the old half-inch stopcock and stub coming from under the pavement, and the improvement in flow was dramatic. The length of new pipe to the kitchen was a bit over two car-lengths. Maybe ten metres? And I teed a similar length up to the loft tanks.

20mm plastic has about the same internal diameter as 15mm copper or 1/2" lead

 

[noseall]

That's widely thought, but I added a 25mm plastic pipe to the old half-inch stopcock and stub coming from under the pavement, and the improvement in flow was dramatic. The length of new pipe to the kitchen was a bit over two car-lengths. Maybe ten metres? And I teed a similar length up to the loft tanks.

20mm plastic has about the same internal diameter as 15mm copper or 1/2" lead

It depends what you are replacing. You can always improve the efficiency of existing pipe by using new pipe - that is undeniable - particularly if you are replacing any of the metal versions (iron, lead, soft copper). But you will get the same improved results from a smaller bore replacement just the same as a larger bore replacement, as long as the water has its origins in similar (small) sized pipe.

 

[noseall]

.

 

[John D v2.0]

It depends what you are replacing. You can always improve the efficiency of existing pipe by using new pipe - that is undeniable - particularly if you are replacing any of the metal versions (iron, lead, soft copper). But you will get the same improved results from a smaller bore replacement just the same as a larger bore replacement, as long as the water has its origins in similar (small) sized pipe.

It sounds plausible but unfortunately that is not correct and physics doesn't bear it out in theory. Let me try to explain.

Pressure loss in a flowing pipe is proportional to length and inversely proportional to the resistance of the relevant section of pipe, (which is related to the diameter.)
If you have 20m of a given pipe, the pressure loss will be say 2 bar at a given flow rate.
If you only have 2m of that given pipe, the pressure loss will be 0.2 bar at that flow rate.
If you have 18m of a wider pipe, you loss in that pipe might be 0.8 bar at that flow rate
If you have 2m of the narrow pipe and 18m of the wider pipe your pressure loss is now only 1 bar rather than 2 bar.

Ultimately you would likely keep the pressure loss similar based on the incoming supply at the street eg 3 bar, and the flow rate would naturally increase to get that pressure loss in daily use,, but that is difficult to illustrate in calculations.

Hope that makes sense! John

 

[thomp1983]

Thought I'd update this as I finally connected the new water supply up yesterday.

In the end I've ended up with, 1m ish of 20mm from the stop cock in the footpath, about 18m ish of 32mm mdpe around the outside of the house to the insuduct, stepped down to a 25mm hockey stick inside the insuduct into the house then used a 25mm to 22mm stopcock to get down to 22mm which is currently temporarily piped across the extension to where the 15mm originally joined the house pipework.

So far the water pressure is hugely improved and definitely been worth the effort involved

Thanks
Chris