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Ben-gee

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Have you considered that your vendor may be selling up to get away from this neighbour?
 

Millsy 82

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I think the first thing I would be finding out is whether you have a water meter and the position.

Next would be the actual size of the pipe my guess 1" would be 25mm which although you could possibly run 2 houses off it I would want the full 25mm for my house only.

Let's be honest the reason the builder has done this is 1 it's probably saving running a new pipe back to the water main and 2 its saving him the cost of getting the waterboarding out to do the connection.

If it was my pipe I would tell him to do one.
 
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Craig Chamberlain

Craig Chamberlain

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Have you considered that your vendor may be selling up to get away from this neighbour?
I don't believe that is the case as they have been neighbours and friends for 12+ years and I know the vendor has other good reasons to move. But I understand why you ask the question.

I think the first thing I would be finding out is whether you have a water meter and the position.

Next would be the actual size of the pipe my guess 1" would be 25mm which although you could possibly run 2 houses off it I would want the full 25mm for my house only.

Let's be honest the reason the builder has done this is 1 it's probably saving running a new pipe back to the water main and 2 its saving him the cost of getting the waterboarding out to do the connection.

If it was my pipe I would tell him to do one.
I don't believe I have a water meter but will need to wait to hear back from Scottish Water on Monday who I have emailed.

The pipe is standard MDPE pipe so is 25mm o/d and 20.4mm i/d

I did some dynamic pressure measurements today which I'd appreciate feedback on. Basically I ran the taps at various flow rates and then measured the pressure while timing the water which flowed in 60 seconds into a measuring bucket. I only have a 4 bar gauge but the needle can pass beyond 4 until it hits the end stop which (assuming it's still linear at that point) would be equivalent to 6 bar.

Flow 0 litres/min - static pressure off the scale of my 4bar gauge so 6+ bar
Flow 5.8 l/m - dynamic pressure still off the scale so 6+ bar
Flow 7.6 l/m - pressure still off the scale so 6+ bar
Flow 12.5 l/m - pressure approx 5 bar
Flow 15 l/m - pressure 3.85 bar
Flow 16.7 l/m - pressure 3.1 bar
Flow 19 l/m - pressure 2.3 bar
Flow 20 l/m - pressure 1.85 bar
Flow 22 l/m - pressure 0.9 bar (kitchen and bath taps both on)
Flow 24 l/m - pressure 0.3 bar (kitchen, bath and utility taps on)

Those last two I had to estimate flow as I couldn't measure them all at once but you can see how the pressure rolls off quickly after 20 l/m

By extrapolating on a chart, I think my static pressure might be as high as 10 bar. Based on that assumption and some distance measurements on google maps I have come up with this prediction about what will happen if both us and the new house supplied from our branch were both to draw 15 l/m at the same time.

Pipe total length 670m. Shared length of pipe before branch 100m. So assuming the pressure drop is equal across the full length, at 15 l/m it is currently dropping 6.15 bar and so 100/670 of that is 0.918 bar dropped in the first 100m with only my house drawing 15l/min.

Pressure drop increases by the square of velocity so if the new branch also took the same water flow, the velocity would double and the pressure drop across the first 100m would quadruple to 3.672 bar. That would in turn cause a reduction in dynamic pressure to me of (3.672 - 0.918) = 2.754 bar at the same 15 l/m flow rate. That means my 3.85 bar would become 1.096.

Anyone know this stuff well enough to check my calculations and assumptions? I tried working with flow calculators but they all hinge around using things like pipe roughness figures which I can't really judge for a 20 year old pipe. So I figured taking actual measurements would be best.

Thanks to all once again.
 

Chuck

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I did some dynamic pressure measurements today which I'd appreciate feedback on.
You've essentially proved that a 25mm is going to be fine for one dwelling but if some clown tries to share it with more houses you're not going to be able to have a decent shower at the same time as your neighbour(s) or have unvented hot water system without installing a whacking great (expensive and large) accumulator.

I suspect that you are falling into the trap of trying to persuade yourself that something that is not okay is going to be okay because you want it to be okay for some unrelated reason.

I wouldn't buy such a property until it had its own pipe that went to it straight from the water company's meter with no funny business. Or, at a pinch, I'd get a professional to specify and quote for an accummulator and knock the cost of the buying price.
 
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Craig Chamberlain

Craig Chamberlain

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You've essentially proved that a 25mm is going to be fine for one dwelling but if some clown tries to share it with more houses you're not going to be able to have a decent shower at the same time as your neighbour(s) or have unvented hot water system without installing a whacking great (expensive and large) accumulator.

I suspect that you are falling into the trap of trying to persuade yourself that something that is not okay is going to be okay because you want it to be okay for some unrelated reason.

I wouldn't buy such a property until it had its own pipe that went to it straight from the water company's meter with no funny business.
I see why you might say that but really I'm just trying to make sure I'm not worrying about nothing because this issue could potentially cause our purchase to fall through and I don't want that to happen without having a really good reason. I think I have done enough research to justify formally objecting to the branching of our main so I'll take that up with the vendor and leave it to him to sort out with the neighbour.

I was just curious really whether my pressure/flow measurements indicate a satisfactory supply at the present. I'm already convinced that they would become unsatisfactory if the neighbour takes half the water away.

Thanks.
 

John.g

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Using a little calc which I have found to be quite helpful and based on the following numbers based on neighbour using same volume of water as you then you can see quite plainly that you will be running out of head when total flow exceeds 40 LPM, ie 20 LPM each, with 40 LPM through the 80 M section and 20 LPM through the 500 M length to your house.
I have done the calc first based on no neighbour teed off the 580 M length. The other calcs are based on 30,40&44 LPM through the 80M length and15,20&22 LPM through the 500M length.

LPM LM DPbar LM DPbar LM DPbar DPbar DPDiff
15 580 2.1 80 1.05 500 1.83 2.88 0.78
20 580 3.6 80 1.79 500 3.11 4.9 1.3
22 580 4.3 80 2.13 500 3.71 5.84 1.54

Can't get numbers lined up above but if one takes the 20 LPM number, the pressure drop is 3.6 bar with no neighbour connected and 4.9 bar with neighbour also using 20 LPM, a difference of 1.3 bar.

 
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Brambles

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If you want to calculate it properly, for MDPE pipe e is around 0.0015mm. Whilst in theory, pressure drop is linear over equivalent length - fittings at the flow end will distort this negatively.
 

Alan Wright

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Hi Craig,
If I were in your position I would seek advise from Scottish Water.
It is the responsibility of Scottish Water to supply water at a minimum pressure and volume. When you bought your house your either paid for or inherited rights to receive a potable water supply at a minimum pressure and volume from Scottish Water. Your neighbour is about to breach this right. Also it is for Scottish Water to approve any connection to their infrastructure. Any new connection is subject to approval and payment of infastructure charges if appropriate. I suspect Scottish Water will be very interested in this.
I am aware of Water Bylaws in England from when I worked for Anglian Water and Northumbrian Water, but I cannot for certain say its the same as in Scotland. I suspect it is the same and if it had happened in my patches the last thing I would want is another DG2 on the list.

Here are a couple of links to get you started but speak to Scottish Water.

1568559501874.png
 
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Craig Chamberlain

Craig Chamberlain

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Using a little calc which I have found to be quite helpful and based on the following numbers based on neighbour using same volume of water as you then you can see quite plainly that you will be running out of head when total flow exceeds 40 LPM, ie 20 LPM each, with 40 LPM through the 80 M section and 20 LPM through the 500 M length to your house.
I have done the calc first based on no neighbour teed off the 580 M length. The other calcs are based on 30,40&44 LPM through the 80M length and15,20&22 LPM through the 500M length.

LPM LM DPbar LM DPbar LM DPbar DPbar DPDiff
15 580 2.1 80 1.05 500 1.83 2.88 0.78
20 580 3.6 80 1.79 500 3.11 4.9 1.3
22 580 4.3 80 2.13 500 3.71 5.84 1.54

Can't get numbers lined up above but if one takes the 20 LPM number, the pressure drop is 3.6 bar with no neighbour connected and 4.9 bar with neighbour also using 20 LPM, a difference of 1.3 bar.

Thanks for taking time to work this out - I get similar figures albeit using the later figures for distances which were 100m from main to branch and another 570m to our house from the branch (670m total). I worked it out at 15 lpm each my dynamic pressure would drop by 2.75 bar compared to if I was drawing 15 lpm with no branch installed.

If you want to calculate it properly, for MDPE pipe e is around 0.0015mm. Whilst in theory, pressure drop is linear over equivalent length - fittings at the flow end will distort this negatively.
Hi - yes I came across the figure of 0.0015mm which I then divided by 20.4mm to get the relative roughness of the MDPE pipe. The thing is, this pipe was installed 20 years ago so who knows what the inside walls look like now and how many joints are installed etc. I think this is why I found it quite difficult to get theoretical calculations to correlate with actual static/dynamic readings taken empirically. You also need to work out the Reynolds number and take account of viscosity due to temperature of the water. I found you can make reasonable assumptions in each case to simplify the equations but could never quite construct a model which worked for me at each empirical flow rate. For all I know there could be leaks or kinks or crushed sections of pipe. This is why I chose in the end to focus on the empirical results with a bit of extrapolation.

Hi Craig,
If I were in your position I would seek advise from Scottish Water.
It is the responsibility of Scottish Water to supply water at a minimum pressure and volume. When you bought your house your either paid for or inherited rights to receive a potable water supply at a minimum pressure and volume from Scottish Water. Your neighbour is about to breach this right. Also it is for Scottish Water to approve any connection to their infrastructure. Any new connection is subject to approval and payment of infastructure charges if appropriate. I suspect Scottish Water will be very interested in this.
I am aware of Water Bylaws in England from when I worked for Anglian Water and Northumbrian Water, but I cannot for certain say its the same as in Scotland. I suspect it is the same and if it had happened in my patches the last thing I would want is another DG2 on the list.

Here are a couple of links to get you started but speak to Scottish Water.
Thanks for that - yes I did email Scottish Water and they eventually got back to me to say that they couldn't really comment on the suitability of the pipe to supply two houses and to consult a professional plumber! So that suggests there are no clear-cut guidelines or rules about pipe size/length for a dwelling. What they did say however is that I (as original pipe owner) would have to consent to my neighbour taking a supply from my pipe and that the new build property owner would have to "consider" (emphasis mine) applying to Scottish Water for a new water connection solely for their property. So even here, they didn't use the word "must" - only "consider".

Anyway, the good news is that our vendor received legal advice in the meantime and then approached the neighbour from a position of knowing he could formally prevent him from using the pipe. But in the interests of good relations, they have agreed that the neighbour will install an upgraded 50mm pipe section between the mains and the branch and this will then be branched to supply each property equally. This is acceptable to me since the 50mm pipe will have a cross sectional area of more than double the 25mm pipe and so my supply should actually improve slightly even when both properties are drawing 20 lpm. It also means that the first 100m of piping are shared and so will have shared responsibility for cost of repair or replacement in future.

So thanks again to everyone who offered advice - very much appreciated!
Craig.
 

Alan Wright

Sponsor
Messages
37
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43
Thanks for taking time to work this out - I get similar figures albeit using the later figures for distances which were 100m from main to branch and another 570m to our house from the branch (670m total). I worked it out at 15 lpm each my dynamic pressure would drop by 2.75 bar compared to if I was drawing 15 lpm with no branch installed.



Hi - yes I came across the figure of 0.0015mm which I then divided by 20.4mm to get the relative roughness of the MDPE pipe. The thing is, this pipe was installed 20 years ago so who knows what the inside walls look like now and how many joints are installed etc. I think this is why I found it quite difficult to get theoretical calculations to correlate with actual static/dynamic readings taken empirically. You also need to work out the Reynolds number and take account of viscosity due to temperature of the water. I found you can make reasonable assumptions in each case to simplify the equations but could never quite construct a model which worked for me at each empirical flow rate. For all I know there could be leaks or kinks or crushed sections of pipe. This is why I chose in the end to focus on the empirical results with a bit of extrapolation.



Thanks for that - yes I did email Scottish Water and they eventually got back to me to say that they couldn't really comment on the suitability of the pipe to supply two houses and to consult a professional plumber! So that suggests there are no clear-cut guidelines or rules about pipe size/length for a dwelling. What they did say however is that I (as original pipe owner) would have to consent to my neighbour taking a supply from my pipe and that the new build property owner would have to "consider" (emphasis mine) applying to Scottish Water for a new water connection solely for their property. So even here, they didn't use the word "must" - only "consider".

Anyway, the good news is that our vendor received legal advice in the meantime and then approached the neighbour from a position of knowing he could formally prevent him from using the pipe. But in the interests of good relations, they have agreed that the neighbour will install an upgraded 50mm pipe section between the mains and the branch and this will then be branched to supply each property equally. This is acceptable to me since the 50mm pipe will have a cross sectional area of more than double the 25mm pipe and so my supply should actually improve slightly even when both properties are drawing 20 lpm. It also means that the first 100m of piping are shared and so will have shared responsibility for cost of repair or replacement in future.

So thanks again to everyone who offered advice - very much appreciated!
Craig.
Nice Result - Well done.
 

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