Why do pipes leak/burst when increasing water main?

[jonwestuk]

I have heard of three people who have had leaks following the install of a larger feed from the main and also was told a few stories from a plumber. Now I am planning on upgrading the main in my house I am trying work out what caused the leaks.

From my GCSE physics, I can't really work out what is going on. The pressure in to the house should not be changing, only the flow/pipe capacity. As the pressure is the same I can't work out why fittings/connections should fail. Plausible options could be:

1. The increased flow puts more force on fittings when the water is turned on or off.

2. The water company increase the main pressure to account for the higher requirement in the street, so pressure does actually increase.

3. Coincidence

4. Alterations to the plumbing change the dynamics within the property making a failure more likely?

So can someone explain what is going on here, and also advise me of what precautions I should take to minimise the risk of s failure?

Thx

Jon

 

[flameport]

Assuming that these third party reported stories are true, then it's most likely coincidence, and most people don't just have the new main installed - they have other work done at the same time.

Perhaps a tiny possibility that draining the system and therefore removing all pressure caused some already defective item to finally fail.

 

[JohnD]

Did any of these people scrap the low-pressure loft tank and change to a high-pressure system?

If not, why did they fit the bigger pipe?

 

[dilalio]

Not everything can be predicted or predetermined - even with the best science!
If parts of a system that were previously low pressure (i.e. Gravity fed heating pipes) are repurposed for high pressure, then chances are joints can fail and leaks occur.
What is the purpose of the new main?
An air test could see if the system stands up but if not, you will need to pinpoint the defects which is difficult with no water indication!

 

[oilboffin]

simple the cross section of the pipe is bigger therefore there is more pressure acting on more surface area when it meets old stuff it creates mayhem

 

[jonwestuk]

Did any of these people scrap the low-pressure loft tank and change to a high-pressure system?

If not, why did they fit the bigger pipe?

That seems to make sense. So hopefully as my house has been running fully from the main for 1.5yrs I should be relatively safe. My pipe upgrade is a future proofing exercise, and to stop having to dig up my bathroom in the future. The current pipe is fine, for my wife and I, but as the family grows having two taps running at the same time will become more important and as I am about to rip out my downstairs bathroom and renovate my front garden it seems like a good idea to make the mains pipe change now.

 

[dilalio]

So does that mean your boiler can cope with an increased flow rate and deliver the results to your hot outlets?

 

[jonwestuk]

It is a good point, that I had already thought of. I plan to add a pressure reducing valve on the water main coming into the house to help resolve this issue. In 5+ years time when I need the extra flow then I will get a larger boiler and open the pressure valve up. All of the connections (water and gas) will be upgraded waiting for a boiler upgrade. I figure that there is no need to pay loads of cash for a new boiler until I absolutely need it.

 

[jonwestuk]

Just thinking out loud, I guess it would be a nice extra to two valves, one on the cold feed, after the combi boiler intake and another just after the boiler hot water outlet. That way I can balance the pressure/flow better across the house. This would be nice as at the moment my cold water has a much faster flow than my hot water.

Is this a stupid idea?

 

[dilalio]

What flow rate do you currently have on your incoming main?
What does it drop to when you open another cold outlet?
Test this at kitchen sink then open garden tap (if you have one).
What flow rate do you have at highest hot outlet?
What boiler do you currently have, how old is it and what is its maximum DHW output capacity?
it may be that you already have enough mains flow to satisfy your future hot water requirements and it is just a matter of replacing your boiler.
Look at boilers that have the DHW output you think you'd need and their size and cost and see if you "already" have the mains supply (by undertaking the tests above) that they require for optimum performance!
Combi boilers, supplying direct hot water, will always produce an 'imbalance' between the hot and cold supplies!
Carry out the flow tests and provide details of them and your current boiler and we can advise you accordingly.

 

[RigidRaider]

Why are you so sure your requirement will increase? Are you having some Syrians to stay?