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Plumbing advice regarding inadequate water supply


Brier
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Hi

Can anyone please provide advice on how to design a water supply system or who to ask to design one for us?

The essentials of the current system are as follows:

The water company facture says the meter has a 20 mm diameter. We therefore presume that the supply to the meter is 20 mm.

The house is 50 metres from the meter and is supplied in 20 mm PE. The same pipe also branches to 3 gites on the way to the house. The total length of external supply pipe is about 70 metres and it is all buried underneath our drive and courtyard.

Interior plumbing in the house commences in 18 mm copper and reduces down mainly to 14 in branches to supply points. Almost everything in the gites is in 14 copper. In total there is a least 50 metres of internal pipe work.

Static pressure measured at the house is just over 3 bars and drops to about 1 bar when a tap is opened. Open another tap and it drops to well below 1. Flow rates range from the barely adequate (10 litres per minute) to the abysmal (less than 4 litres per minute) depending on where on the system they are measured and that’s with only 1 tap open.

The maximum number of people that the system would need to serve is 19 although a more normal load would be 12.

We know that the supply pipes are under sized and are resigned to the time, money and disruption required to upgrade them. We do, however, want to be sure that we end up with a system that “works”.  Internet searches on pipe sizing have yielded mixed results varying from “rule of thumb” estimations to complex formulae that would require a degree in maths to follow. Consultations with our local plumber have not inspired much confidence either – Too much head scratching and shoulder shrugging.

So our questions are as follows:

1.    Can anyone advise on the size of pipes required?

2.    Would increasing the size of the pipes on our side of the meter make any difference if the external supply size remains the same?

3.    Should a “normal” plumber be able to design an adequate system or do we need a specialist?

4.    Is there any feasible alternative to replacing the external supply pipes? Someone has suggested that we install booster pumps in each property but we fear that the supply flow rate would be insufficient.

Sorry for the long post. All advice gratefully received.

Thanks in advance.

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With low pressure your options are limited.

A local storage tank to give you a head might be a possibility although I have no idea of the legalities of such an arrangement.

Are you sure you don't have a blockage somewhere though. There is normally a filter on the feed side of the meter and it's surprising the amount of crud which can accumulate there and restrict the flow ?

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I am sure it is not allowed to store water in France.

Upping the size of the pipes post meter would help to remove restriction but will do naff all if it's not a restriction causing your problem.  Your problem sounds lie a flow rate problem, pressure is a product of resistance to flow, if you have good pressure at your meter and poor pressure at the tap then you have a lot of resistance in the pipe work between the two.  Maybe a good idea to install a gauge at the meter.  Avoid tight bends in pipe work, going as big as you can (realistically) will help. You are introducing a big restriction straight away with an 18mm pipe off the 20mm one, 2mm might sound like nothing but it reduces your internal area by 1/6th.

I am no plumber btw but most of it is common sense.

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Also not a plumber but some things are pretty basic.

Generally the standard supply side pipe to the meter is thick wall plastic with an O/D of 25mm and I/D of 18mm and would continue in similarly from the meter to the property. If you have only 20mm O/D from the meter on then depending on it's wall thickness the I/D could be as little as 14 or 15mm which is far too small, you then further compound the problem by splitting it 4 ways.

The first thing you have to do I think is check the pressure directly at the meter to find out what you have actually got. If it really is only 3 bar then I think you have little or no chance of supplying 4 properties and the only option may be to install a pump, possibly even separate pumps for each property. Boosters at each property will be useless as you need to push the water from the source not pull it.

Whilst you're checking the pressure also run the water briefly straight out of the meter to see what the actual flow rate is like, if you have a large container you could crudely measure it in lt/min, best to use a piece of pipe of the same dimensions as the incomer for that to eliminate variables. Without knowing the pressure and flow rate it's next to impossible to design a system or plan how to best overcome any shortfall.

Low pressure or not if I were looking to feed 4 properties in this fashion it would be with separate feeds taken direct from the meter via a manifold. That way each property would get a fair shake.

Do we take it you have installed this system yourself ?

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I always thought that the pipes in the house reduced in size as you move away from the stopcock, this is to ensure the pressure stays the same throughout the house and why the French have so many different pipe sizes. It stops the problem of somebody running a tap in the kitchen and the person jumping out the shower because the water has quickly changed in temperature. It has a similar effect to putting your finger over the end of a hose. The other thing is if you say the pressure is correct at the stopcock then firstly how do you know this or is that an assumption? In towns and villages the water pressure is typically six bar then reduced to three bar either at the water meter or just as it enters the house (normally) so where is you pressure reduction valve and is it working OK. Water pressure in some rural areas can of course be lower as some will know. With regards to pipe diameter, as far as I know its the inside size that is always quoted so if you measure the outside diameter of the plastic pipe and think its 20mm it may actually be 18mm inside because plastic pipe walls are thicker. If it says 20mm on the outside of the plastic pipe then it will obviously be much bigger on the outside.
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[quote user="Quillan"]Not always, ours is taken from the river, filtered then pumped to about 200 houses.[/quote]

Usually we get water from the water tower at Lamairé, pumped with flygt pumps from the tuffaceous karstic reservoir overlying an impermeable marnes horizon located in the Seneuil Valley.

Unusually we get water from the treatment and pumping station close to the dam on the Cebron Lake; this unusual and usually[:P] only occurs after torrential rain when some turbidity of the artesian water from the Sources de Seneuil can occur.

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[quote user="Brier"]

The water company facture says the meter has a 20 mm diameter. We therefore presume that the supply to the meter is 20 mm.

[/quote]

I think that is the place to start, is it a 20mm supply or larger and just "T'd" off in 20mm. if it's larger then running off the additional supplies from main with their own meters is the way to go.

Time to start digging

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" Static pressure measured at the house is just over 3 bars and drops to about 1 bar when a tap is opened. Open another tap and it drops to well below 1. Flow rates range from the barely adequate (10 litres per minute) to the abysmal (less than 4 litres per minute) depending on where on the system they are measured and that’s with only 1 tap open. "

What is the flow rate in the 18 mm or whatever size pipes immediately after the meter. If that flow rate is adequate larger diameter pipes in the house will help.
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Many thanks to all for the responses.

We measured the pipe diameters. The underground supply from the meter to the properties is a single 20 mm external diameter black plastic pipe (the type that we used to know as "alkathene" in the UK and I believe is referred to as "PE" here). We have not measured the internal diameter but specifications that we have read for this type of pipe suggest it should be about 15 mm.

There is a pressure regulator immediately after the meter. We contacted the water company and they have checked for blockages on "their" side, changed the meter and advised us to change the pressure regulator which has been done.  This improved the situation a bit to its current inadequate level. We have measured the pressure in the system as 3 bars when no water is flowing. I thought that the pressure should equalize throughout the system when there is no flow and that it doesb't matter where it is measured. Is that not the case?

We did not design or install the current system ourselves. We have made some changes and additions inside the properties but we "inherited" the extrior supply network. As far as we know, the main supply to the house was installed in the 1970s during a major renovation and the branches to the gites have been added by local builders at intervals since then.

We know that the current system is inadequate. What we need help with is designing an adequate system or advice on where to find that help.. We do not want to embark on an expensive and disruptive project if poor design means that the end result is only going to be a marginal or no improvement. As stated before, our local plumber has not been much help.

Thanks once again.

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As the water company has already checked for blockages and changed the meter they should be able to confirm what the size of the supply pipe is, (don't assume) that is the single most important piece of information you need to decide if your project is a go or stop.
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[quote user="Anton Redman II"]" Static pressure measured at the house is just over 3 bars and drops to about 1 bar when a tap is opened. Open another tap and it drops to well below 1. Flow rates range from the barely adequate (10 litres per minute) to the abysmal (less than 4 litres per minute) depending on where on the system they are measured and that’s with only 1 tap open. "

What is the flow rate in the 18 mm or whatever size pipes immediately after the meter. If that flow rate is adequate larger diameter pipes in the house will help.[/quote]

We have crudely measured the flow rate immediately after the meter and pressure regulator this afternoon and as best we can tell it is about 33 litres per minute.

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[quote user="Théière"]As the water company has already checked for blockages and changed the meter they should be able to confirm what the size of the supply pipe is, (don't assume) that is the single most important piece of information you need to decide if your project is a go or stop.[/quote]

We excavated the supply pipe to the meter this afternoon (It's not visible in the meter "box" as the shut off valve is tight against the side)  and it is in fact 25 mm external diameter so you are right and we were wrong to assume. The meter is still labelled as 20mm though)

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3 bar doesn't sound like much to me.

With all the outlets off you have no flow so pressure should be maximum and will be equal across the system.

Open a tap and in an ideal world you will get maximum flow through the system to the tap.  This will result in zero (static) pressure at the meter (there will be a small amount of dynamic pressure but not much).

If you have pressure still showing at the meter it will be because of resistances to flow within your system.

Your check valve could be a big restriction.  Do you know what the pressure is before the meter and regulator?

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Placing a regulator immediately after the meter with a further several 10's of meters to the property seems odd and makes me wonder why anybody would do that. Could it be that the 20mm pipe is under spec thin wall and the reducer is to prevent possible bursting ?

I think you need to find out exactly what that pipe is as if it is thin wall then it will probably rule out any ideas of pumping more pressure through it.

Did the water company tell what the pressure was on their side ?

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From what I read it does not matter which 'end' the pressure valve is although in most cases (but not always) it's near the meter that being the case why not place a valve just before the main stop-cock in each property and remove the one by the meter? As AnOther says you need to look at the pipe, try and find a number of something to see the pressure it can take. It's probably OK but you don't want it to blow on you, its a real bind digging up half your garden to find the leak. This may also be the cheapest route if the pipe is OK.
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[quote user="crossy67"]3 bar doesn't sound like much to me.
Your check valve could be a big restriction.  Do you know what the pressure is before the meter and regulator?
[/quote]

That's the next bit, supply pressure before the meter, increasing your pipe size after the meter to 25mm will reduce the friction loss (head loss) and increase the supply potential by more than 50% over the bulk of the supply run. It could be worth running at a higher pressure from the meter to closer to the building and possibly reducing the pressure at that point.

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[quote user="Quillan"] As AnOther says you need to look at the pipe, try and find a number of something to see the pressure it can take. It's probably OK but you don't want it to blow on you, its a real bind digging up half your garden to find the leak. This may also be the cheapest route if the pipe is OK.[/quote]

We've been able to have a close look at a 2 metre length of the 20 mm supply pipe because we had to dig up a section to find a burst a year or so ago.  We can confirm Quillan's opinion that it is a real pain!

We had forgotten we had it lying at the back of the barn. There are no markings whatsoever on the pipe and certainly not the blue stripe found on modern pipe. The section that we removed has an internal diameter of 15 mm and a wall thickness of about 2 mm. We would be reluctant to put more pressure through this pipe given that we have already had a leak.

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Handy site here.

http://www.ukcopperboard.co.uk/literature/pdfs/Installation-Tips/Pipe-sizing-basic-principles.pdf

And here.

http://flexpvc.com/WaterFlowBasedOnPipeSize.shtml

A19mm ID valve 117mm long will flow roughly 227 litres/min.

Unfortunately I can only find gal/min tables but it will give you an idea what upping the pressure in an ideal system will achieve.  At 40psi (2.75bar) a 1" (25.4mm) pipe will flow 38 gal/min (172 l/m).  If you up the pressure to 60psi (4 bar) your flow goes up to 213 l/m. 

Increase the pipe size from 19mm to 31mm and your flow at 40psi will go up to 309 l/m so you will get 136 l/m more, more than doubling your flow rate for 12mm bigger diameter.  This is assuming your meter is not the restriction and your plumbing is totally efficient (impossible).  Would it not be possible to up your water pressure, obviously you need to make sure your plumbing is capable of handling it and your meter and valve can handle the extra flow.

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[quote user="AnOther"]I'd say that you are rapidly approaching the solution I posted earlier, a full pressure manifold at the meter and separate 25mm pipes to each property, augmented with collective or individual pumping if necessary.

[/quote]

Glad you said that because I was starting to think along the lines of how much a mini digger will cost to hire down that neck of the woods. Combining your thoughts with the post after yours why use a manifold, why not run a 'backbone' of a reasonable size, at least that of the pipe feeding the meter then 'T' off at each property then fit a pressure reducer just before the stopcock in each property?

Anyway which ever way you go about it I think there will be some digging involved. The most important thing is to really know what pressure is on the feed side to the meter first, hopefully it will be around six bar.

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[quote user="Théière"]

Plenty of pipes available and at 16 bar plenty of safety margin.

Brico..........

[/quote]

I use it...freezes every third year or so.....15 minutes with a hair dryer....all fixed.

Resists earth tremors....global warming....global cooling.....sunspot activity....ultra-violet light.....nuclear radiation....

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