New water main to increase pressure/flow

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Hi all,

Water pressure and flow rate are not brilliant, British Gas said the flow is too low for a combi-boiler. So I fancy replacing the very old (not lead) water main with 25mm or 32mm mdpe. I know all the caveats, 750mm deep, lined with sand, keep the trench open until inspected etc. Few questions:

Length, house to pavement stop-cock ~15m.

1. I guess a larger bore pipe just increases flow (not pressure)(?)
2. Will the water company increase the pipe diameter between the water main in the street, and my pavement stop-cock?
3. If the answer to (2) is no, then will I achieve anything replacing my part of the pipe?
4. Can the water company "do" anything (other than ensure my stop cock is fully open) to increase the water flow rate, without digging?

Thanks for your help!
 
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1. Yes.
2. Probably if you pay them enough.
3. Pipe needs to be same dia from the main or I doubt you'll se any benefit..
4. No.

If the main in the street has been cleaned and lined in the past it is possible cement has partially blocked the ferrule, thus restricting flow/pressure to the property.
 
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Thanks for your "concise" reply, raises a few more questions tho'!

Pipe diameter doesn't affect "static" water pressure, but dynamic pressure (once a tap is on) is reduced, isn't it?

United Utilities will connect my new pipe for free, so it's not down to what I pay them. As the street water main could be anywhere (eg across the street), isn't it unlikely they'll replace the pipe on the far-side of (my) street stop-cock?

You raise a good point at the end. The street main has (apparently) been lined with a polythene pipe (can't imaging how!), so it is possible that there is a cement blockage. What's a ferrule??
 
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Bit rusty on the pressure question so will have to leave that to someone more knowlegeable. Logic tells me if a tap is turned on then pressure will reduce elsewhere, as the static pressure is governed by the supply variables.

Whilst UU will connect for free, this probably only covers the new supply you've laid to the boundary to the existing supply from the main. They'll disconnect existing service and connect new in its place. (Unless you're lucky and the main is immediately outside the boundary, then they might connect to that.) If there's a polythene main thats been retrofitted inside existing pipe then reinstatements where excavations to connect the service pipes may be visible.

Lining can be done by various methods. Firstly, holes are dug at appropriate points to access the existing (Iron) main. One method is where sections of polythene pipe are 'Butt Welded' together to form the required length. The existing main is isolated and drained. The new length of pipe can be either dragged through using the existing iron main as a host pipe, or if a bigger diameter pipe is required, then a specialist 'mole' is pulled through the existing pipe, splitting it as it goes and forming a larger space into which the new polythene pipe is installed, being dragged behind the mole.

Another method is cement lining. Pipe is accessed and drained. Cleaning is carried out using scraping tools that are either winched through, or attached to mechanically driven steel rods. Once clean, a cement lining is sprayed onto the wall of the pipe and allowed to cure before main is recommissioned. However this method can result in cement blocking ferrules.

The ferrule is the fitting tapped into the top of the main to which the service pipes are connected. Usually fitted without having to isolate the main, a hole is cut into the top of the main, a tap is driven in to cut a thread and then the ferrule screwed in. (Hard work on an iron main!) Doesnt always go to plan, if it doesnt then you can get very wet. :LOL:
 
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3. If the answer to (2) is no, then will I achieve anything replacing my part of the pipe?

There is a useful website for calculating pressure drops in pipes at http://www.pressure-drop.com/. As an example if you had 20mm MDPE pipe (approx 15mm ID) from the main then at 30l/min the pressure drop along the 15m to your house would be around 0.9bar. If you used 25mm MDPE then the pressure drop will fall to around 0.2 bar.

If you can't increase the size of all it and have to leave some at a smaller size it doesn't necessarily matter. 14m of 25mm MDPE and 1m of 20mm MDPE would give you a pressure drop of 0.27 bar; still a substantial improvement.

Unless you have several taps all connected to the main, as opposed to the CW tank, then it will be difficult to really measure the maximum flow you can get. If you do have a few available then open them all up to full flow at the same time and using a bucket and a stopwatch measure the flow from each to get the total.

It may be easier said than done, but before digging up your drive it would be worth connecting a pressure gauge, eg. Screwfix part 82412, to a point somewhere near the stopcock. You could then measure the pressure with no flow and full flow and that would give you an indication of how much pressure drop there is along your 15m mains supply. I wouldn't dig up my drive on the basis of what BG said.
 
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Wow! some really knowledgeable replies, thanks!

Hugh, it sounds like you've laid new water-mains. I read your post with interest.

dumbrill, ta for the pressure drop info - probably the key to what I was asking about. As I use Linux, I didn't download the calculator - will nab wifeys laptop! I will have to spend a little time with the on-line calculator, and try to get the grey matter around the problem.

The gauge on Screwfix also looked good, might buy one.

Hmm, some thinking to do, and points to consider!

Thanks again...
 
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