Water pressure

[zad3717]

Probably half-inch internal bore then. You will benefit from bigger.

Are the pipes inside the house 15mm copper?

Start with the kitchen sink cold tap, and the garden or utility room if you have them.

I expect the hot taps will be a bit less.

Yes 15mm at the stop cock…

 

[Madrab]

You want to test the cold water mains at the closest point to the mains stop tap, on a full bore tap that has 15mm/22mm pipe all the way to it to obtain an accurate reading.

Run a couple of taps within the house while doing the test as that will indicate the dynamic pressure and flow.

15mm pipe doesn't necessarily dictate low flow, if the mains pressure is 3 bar dynamic then 15mm pipe will happily flow 20+L/Min, it just starts to get noisy once the water velocity increase above 2m/s and wear can then become a factor longterm. Ideally though the main distribution pipework within the dwelling shouldn't be any less than the mains itself, that will maximise flow to the outlets.

 

[JohnD]

I haven't seen calculations, but I certainly found that increasing size of supply pipe and stopcocks made a dramatic increase to flow in my previous house.

 

[Madrab]

I haven't seen calculations, but I certainly found that increasing size of supply pipe and stopcocks made a dramatic increase to flow in my previous house

Of course a larger diameter pipe will always flow more if the dynamic pressure is available to sustain it or bottlenecks are reduced. That being said a 15mm pipe will still deliver similar volumes albeit at a higher velocity, as long as the dynamic pressure is available to sustain it. At the opposite end though, a mains with very poor dynamic pressure (<1bar) and flow wont benefit much when increasing the pipe size, in fact it can actually reduce performance as the pressure can't sustain the flow.

Usually though it comes down to pipe sizing calculations (working pressures/loading units/fittings etc) and the desire to maintain the velocity of water below 2m/s to avoid excess noise and friction whilst still satisfying multiple outlets with an adequate volume.

Hence the need to understand dynamic pressures and flow before any decision is made.

 

[JohnD]

a mains with very poor dynamic pressure (<1bar) and flow wont benefit much when increasing the pipe size, in fact it can actually reduce performance as the pressure can't sustain the flow.

Like a loft tank, feeding an upstairs bath tap with a 22mm pipe?

Reduced performance?

Surely not.

 

[Madrab]

Like a loft tank, feeding an upstairs bath tap with a 22mm pipe?

We're talking about mains pressure feeding through a whole house. Indeed, a 22mm feed from a CWSC to full flow taps will of course increase the flow to that tap under gravity.

When looking at a mains though with really low dynamic pressure, increasing the whole house to 22mm pipe everywhere with high flow outlets then when using several outlets at once then that flow can drop off much faster.

Perfect example is one of my client, lives at the top of a 5 storey tenement. Opposite is a swimming baths. They're main bathroom is fed by a communal cistern in the loft, great flow to the bath and basin through 22mm. When the swimming pool across the road is doing pool maintenance, the water pressure drops to less than 1/2 bar, and the flow to the en suite that has 22mm on the mains to all the cold drops to a trickle whilst their kitchen sink run from 15mm still has enough flow to fill a kettle albeit it slowly. The only conclusion is that there isn't enough pressure to sustain any kind of reasonable flow through the larger diameter pipe. We've tried everything to maximise the flow (full flow everything and a mains pump is not allowed as it's a tenement and could starve the neighbours below). It's great when the pressure is up but not when it drops. There is a local plan in place now to increase the district main and add a new local pumping station as a lot of properties are affected.

 

[Dereekoo]

in fact it can actually reduce performance as the pressure can't sustain the flow.

.

Impossible, the flow through a pipe is governed by the pressure (static or dynamic) at the start of the pipe together with the friction within the pipe to its discharge point. All things being equal a larger pipe will resist the flow less than a smaller one hence performance cannot be reduced (it can stay the same if it is conditions further upstream controlling the flow forward)

 

[Madrab]

Not if the volume of water it has to move is greater as in a larger pipe, very low pressure wouldn't be able to move that water at the same velocity as the reduced pressure has to overcome the greater 'weight' of the water. If you take an open ended 15mm pipe and the same of a 22mm pipe and apply the same very low pressure to it, the flow from the 15mm pipe will travel farther than the 22mm pipe as the velocity would be greater. That's why you can make the water travel farther by restricting the end of the hose with a finger so the perceived flow is greater, even though the volume isn't

All I'm suggesting is that under the same poor mains conditions a tap fed by a 22mm pipe may have less perceived flow than a smaller dia pipe.

 

[bernardgreen]

a tap fed by a 22mm pipe may have less perceived flow than a smaller dia pipe

The perception of flow is very often based on the velocity of the liquid leaving the orifice ( such as the spout of a tap ) which can provide mis-leading values for flow rate. Small orifice and high velocity can appear to be more flow ( it's faster ) than a large orifice and slow velocity when in reality the flow from the larger orifice is ( much ) the greater flow.

 

[Madrab]

Yes and when that comes to user interaction then it is seen as an impact to users performance, so that probably my poor choice of words.

That being said it wasn't really in relation to the OP's requirement to obtain actual dynamic flow and pressure readings, so my fault again for sidetracking.

 

[zad3717]

evening, so I get at the kitchen sink approx 6l per minute... 6 seconds on full gave me 600ml of water. ideally this should be 10l per min?

so there is obviously some bottle neck somewhere, I will get the plumber to test from the stop cock flow there then work out what to do next from that point...

Thanks for all the thoughts and advice

 

[Madrab]

ideally this should be 10l per min?

Ideally it should >20L/Min but that's when everything is going well.

Your water transporter will have a min they are obliged to deliver as part of their service contract to their customers, this can range from 8 > 12L/min. As you suggest get an unfettered mains test first.

You could actually call out your supplier and tell them you are having issues with your water supply and can they test the mains outside you property and that should give you an idea of what the mains is delivering.

Be in when they arrive and be nice and get the tea and biscuits out and get them to do a full pressure and flow test

 

[Dereekoo]

Ideally it should >20L/Min but that's when everything is going well.

Your water transporter will have a min they are obliged to deliver as part of their service contract to their customers, this can range from 8 > 12L/min. As you suggest get an unfettered mains test first.

You could actually call out your supplier and tell them you are having issues with your water supply and can they test the mains outside you property and that should give you an idea of what the mains is delivering.

Be in when they arrive and be nice and get the tea and biscuits out and get them to do a full pressure and flow test

OFWAT GSS (guaranteed standard of service) states that a minimum pressure of 0.7bar must be maintained at the communication pipe, there is no spec on flow rate.
The-guaranteed-standards-scheme-GSS-summary-of-standards-and-conditions.pdf (ofwat.gov.uk)

 

[zad3717]

Ideally it should >20L/Min but that's when everything is going well.

Your water transporter will have a min they are obliged to deliver as part of their service contract to their customers, this can range from 8 > 12L/min. As you suggest get an unfettered mains test first.

You could actually call out your supplier and tell them you are having issues with your water supply and can they test the mains outside you property and that should give you an idea of what the mains is delivering.

Be in when they arrive and be nice and get the tea and biscuits out and get them to do a full pressure and flow test

UU our water provider are coming to have a look in a couple of weeks they can give me some advise etc.

 

[Madrab]

here is no spec on flow rate.

yep, can't argue with that publication but I guess it depends on what section the info comes from

The DG2 (level of service indicator) tests @ 1bar @ 9L/Min as it's min SLA in England and Wales. https://www.ofwat.gov.uk/publications/water-pressure/

Up here in Scotland the bylaws are different. I need to check as it's been years since I did my regs and bylaws though they state the min as a pressure and flow rate too.