Mains water supply pipe sizing

[Ian]

Hello All, Just been reading the thread on "Pressure and flow changes 22mm to

15mm" with interest.

My mains water supply is slowing down. It is beginning to struggle with driving the electric shower. I have had the water supply company rep who measured the pressure (at 4.5bar, which is what he expected) and flow rate (8litres/min) which was a lot less that he expected. He advised that he knows (he has been the water company's man in this area for many years) that the (shared) supply pipe from the main to our property - and the other 2 properties on the pipe - is well furred and overdue for renewal. He is suggesting that I renew the pipe back to the main with MDPE and separate my supply from the other 2 properties. Note: getting agreement with the other residents is likely to be prove somewhat difficult - absentee landlords and the like.

Now...to the questions.....

The pipe will run around 220 meters from the main to my stopcock in the house. It supplies normal domestic water requirements with occasionally use to top up animal water troughs (by removable hose).

Given the pressure at the main of 4.5bar can anyone tell me how to calculate the flow rates for the different sizes of MDPE pipe (20/25/32mm)? What flow rate should I be aiming for?

I am very much in favour of separating my supply from my neighbours, am heartened by the relatively small cost that the Water Company want for providing my new connection and believe I can get the trench dug and pipe laid relatively cheaply ('tis easy digging)

Has anyone done this sort of thing? Any pitfalls?

Many TIA Please reply to group - email address is not monitored Ian

[Phil L]

The maximum available.

I've dug out and installed probably 2 to 3 hundred water mains for central heating companies on behalf of local authorities (council houses)....the only pitfalls are other services, especially if you are intending using a digger.

Try to find out where your gas and electricity mains enter the property and then guess as to where they connect up to the main feeds, then try to avoid them, or be extra cautious if they can't be avoided.

Make sure the main is lagged with 150mm lagging where it enters your property and also the mdpe and lagging should be inside a rigid plastic ducting.

Use a trench whacker when backfilling, this minimises sinking later on.

[Ian]

Other services not a problem .....overhead electricity, no gas and no drains! 150mm(!) lagging. Is this a typo? That means o/d of lagged pipe about 13 inches by my reckoning. I actually intend terminating the new supply at the point of the existing meter point since all pipework 'my' side of that is plastic already. From memory, when it was installed 20 years ago there was no lagging on it whatsoever, but that was done professionally by the water company so no surprise really! Please reply to group - email address is not monitored Ian

[sm_jamieson]

Note that if you have a shared pipe, you must ensure that no dead leg is left over. This means finding the connection between the shared pipe and the pipe to your house, and removing your branch there. If this is under the neighbour's garden, you would need their permission to dig it up ! This situation is more likely if you are on the end of the pipe. (Guess what, that is where I am !) Also note, you may be able to get some of the work paid for on the lead replacement scheme if your water company does one. Simon.

[Jonathan]

My local water supplier, Severn Trent, have a scheme whereby they will do the work from the property boundary to the mains for free when it is a question of providing separate supplies for properties that currently have a shared supply. It might be worth checking with your local company to see whether they have a similar scheme. There were conditions but we managed to meet them fairly easily (off-hand I can't remember what they were but there was a magic phrase their inspector gave me to mention when I called them).

Jonathan

[sm_jamieson]

I'm ST too, was this the lead replacement scheme, or just about shared supplies ? Did you have an issue with not leaving a dead leg when your old mains was disconnected ? Simon.

[Jonathan]

Not it wasn't lead, it was specifically about shared supplies. We own one building with three dwellings, which had a 1/2 inch shared supply when we bought it. Building regs said we had to put in larger separate supplies as part of our renovations ongoing. We haven't done this yet but I can't see there being an issue with a dead leg for us as the original supply splits inside the building, so we should easily be able to remove the old pipe when the new connections are made.

Jonathan

[Ian]

Hi Jonathan, That is interesting. I suspect this may be reflected in the relatively low cost of connecting the replacement pipe to the mains. There is no lead so I cannot use that as a lever either. The property boundary is about half way so they would need to do 100m of pipe. I shall certainly ask them when I contact them for the spec. of work they require. Thanks

Please reply to group - email address is not monitored Ian

[Ian]

Hi Simon Thanks - Dead leg should not be a problem. I'm the first in the line and my neighbours all 'T' off just before my present meter position (under my concrete drive - joy!) Legally, the pipe from this point back to the mains belongs to, and is the sole responsibility of, one of my neighbours who , I just know, is not going to do anything about it. Rather than replace this pipe for the benefit of all , I'm afraid I am being rather selfish and just looking after my own supply by putting in a separate supply back to the mains. I am tempted to double up the supply pipe for this length ( since it crosses not only my land but a neighbouring field - not owned by any of the neighbours on the pipe!) in the hope I can sell the 'spare' to my neighbours at some ridiculous profit when the existing pipe finally breaks or furs up completely...... but that seems a bit mean and lowers me to their level. I already have the right and the permission to dig to replace the pipe, but thanks for making the point Cheers Please reply to group - email address is not monitored Ian

[Phil L]

No, 150mm is the total diameter of the lagging!

They are a law unto themselves - the inspector want's to see it 30 inches down before he will pass it, yet the lads who come connecting up moan about the depth, given that their 'main' main is usually about 20 - 24 inches down.

The lagging is compulsory only where it goes under the foundations or through the wall - apparently there is a 'cold spot' at the point where it leaves outside and comes inside!!