Adjusting the PRV to go to 4 bar..?

[dblvkrb]

We've installed a new 25mm water mains in to replace a led mains in and the pressure is so high we've had to put pressure reducing valve on and cap at 3 bar.

The flowrate from the tap is about 10 litres per minute but we're expecting at least 15l/m. The taps/showers are rated to 3bar but I want to find out if anyone thinks there is a great risk in adjusting the PRV to 4bar to increase the flow.

For info, the combi storage boiler is rated for 18l/m and the current Plumbing has been power flushed, no issues. Any advice appreciated?

 

[Aire]

Pressure and flow are two different things, upping the pressure reducer to 4bar will likely have no impact on the flow rate.

 

[Rob Foster]

We've installed a new 25mm water mains in to replace a led mains in and the pressure is so high we've had to put pressure reducing valve on and cap at 3 bar.

The flowrate from the tap is about 10 litres per minute but we're expecting at least 15l/m. The taps/showers are rated to 3bar but I want to find out if anyone thinks there is a great risk in adjusting the PRV to 4bar to increase the flow.

For info, the combi storage boiler is rated for 18l/m and the current Plumbing has been power flushed, no issues. Any advice appreciated?

No never , you might well be creating a pressurised bomb
Combi set ups operate at 1.5 bar
And no more ever. There have been accidents ! With over over pressurised unvented systems
I know it’s my specialist area
Centralheatking

 

[townfanjon]

^^^^^^^^^ sake

 

[townfanjon]

As Craig says very little if any difference, flow is increased by correct pipe seizing .

 

[Riley]

Safety feature NO pressure and flow are not the same

 

[Riley]

Would advise speaking to local water board to see what pressure and LPM you could possibly expect in your road then if that is ok look at the pipework to and from the boiler

 

[dblvkrb]

When the new mains in was originally plumbed without the PRV the water was bouncing out of the sink, so it must be related to the flow to some degree. I absolutely agree about potentially creating a time bomb.

Let me ask this a different way, what flow would you expect on average with good pressure and a high spec combi, what other things can I do to improve the flow rate from the shower or taps?

 

[dblvkrb]

Would advise speaking to local water board to see what pressure and LPM you could possibly expect in your road then if that is ok look at the pipework to and from the boiler

There is a great deal of pressure, this isn't the issue.

 

[Riley]

As we’ve said though flow and pressure are different. Alright ignore pressure ask the water board what you should expect. If you are a way off that it’s time to start testing.
Is the strainer filter on the prv blocked?
If you rig up a tap or pipe straight after the stopcock what do you get then flow wise??
What does the incoming reduce to after the stopcock, 25-??

 

[Aire]

The water bouncing out the sink shouldn't have been affected by installing a pressure reducer as technically these restrict standing pressure, not working pressure (or at least thats my understanding of them). Basically the standing pressure of your system will be exactly the same as before you installed your new water main so you don't have anything to worry about regarding tap rating etc. I'd turn your pressure reducer up to max, then run the tap and slowly turn the valve down until you achieve your desired flow rate.

 

[ShaunCorbs]

When the new mains in was originally plumbed without the PRV the water was bouncing out of the sink, so it must be related to the flow to some degree. I absolutely agree about potentially creating a time bomb.

Let me ask this a different way, what flow would you expect on average with good pressure and a high spec combi, what other things can I do to improve the flow rate from the shower or taps?

Off the stop tap to the prv what size pipe

Also what size is the prv 15mm

Pipe size off the prv to the boiler ?

 

[Riley]

The water bouncing out the sink shouldn't have been affected by installing a pressure reducer as technically these restrict standing pressure, not working pressure (or at least thats my understanding of them). Basically the standing pressure of your system will be exactly the same as before you installed your new water main so you don't have anything to worry about regarding tap rating etc. I'd turn your pressure reducer up to max, then run the tap and slowly turn the valve down until you achieve your desired flow rate.

PRV doesn’t affect flow

 

[Aire]

PRV doesn’t affect flow

That's what I thought too but op installed a new water main, had too great a flow rate, installed a prv and now flow isn't so great. If turning the prv up increases his flow to what he classes as desirable then it's an easy fix

 

[Riley]

That’s not how it works

 

[Aire]

That’s not how it works

How can you be so sure? What if op's working pressure is 3 bar and the pressure reducer is set at 3 bar?

 

[Riley]

I’m not sure I get your point. If incoming is 3 bar and prv is set to 3 bar then 3bar give or take will pass through it

 

[ShaunCorbs]

That's what I thought too but op installed a new water main, had too great a flow rate, installed a prv and now flow isn't so great. If turning the prv up increases his flow to what he classes as desirable then it's an easy fix

That's pressure

How can you be so sure? What if op's working pressure is 3 bar and the pressure reducer is set at 3 bar?

Prv don't adjust flow just pressure

Just because it's not splashing all over the place at reduced doesn't mean it's not the same flow just less pressure

 

[Riley]

Flow is impacted by correct pipe sizing, obstruction or restriction in the pipework and can also be controlled by reduced lpm sanitaryware

 

[Pickwickpick]

As Riley and others have said pressure and flow are not the same thing. A PRV could have sorted out the splashing tap but will not have affected flow.

As an example:

If we have two taps both with a flow rate of 15 lpm where tap no1 has 6bar pressure and tap no2 has 3 bar pressure, both will fill the sink up in the same amount of time. But when taps are turned on tap no1 will splash much more violently off the surface of the sink due to the much greater pressure than tap no2. i.e. its the same amount of water but coming out with more force, turn the pressure down and water hits the sink with less force so doesn't splash/bounce but its exact same amount of water per minute hitting the sink.

 

[Aire]

Flow is impacted by correct pipe sizing, obstruction or restriction in the pipework and can also be controlled by reduced lpm sanitaryware

Yes I know that, and I'm not trying to argue with you about the difference of flow and pressure.
Read op's post, he says after installing a new water main, his flow was that good that water was bouncing out the sink. So to correct this, he installed a pressure reducer (I know this technically shouldn't change anything). Since installing the pressure reducer, his flow rate has dropped, again I know this technically shouldn't happen, but if he has a high working pressure it could be interfering the pressure reducers function. Basically if the pressure reducer is set to 3 bar and his working pressure is 3 bar or slightly higher then the valve may be opening and closing repeatedly as the pressure required by the prv will be constantly achieved. Sorry if that sounds confusing, in my head I know what I mean, it's just hard writing it 😕

 

[Riley]

I would be looking for an obstruction clearly something has changed but it won’t be the PRV purpose that has caused it

 

[Riley]

Also going above 3bar can impact other things such as the boiler from a safety perspective

 

[Riley]

to be honest it could be something as simple as some muck from the new mains install getting trapped in the new PRV and affecting flow

 

[dblvkrb]

As we’ve said though flow and pressure are different. Alright ignore pressure ask the water board what you should expect. If you are a way off that it’s time to start testing.
Is the strainer filter on the prv blocked?
If you rig up a tap or pipe straight after the stopcock what do you get then flow wise??
What does the incoming reduce to after the stopcock, 25-??

The PRV is brand new, is it likely the filter would already be blocked? I haven't experimented with running a tap straight off the mains stopcock but it's a good idea.

After the stopcock it reduces to 10-11 l/m, up to 12l/m if running purely off of the cold mains.

 

[ShaunCorbs]

The PRV is brand new, is it likely the filter would already be blocked? I haven't experimented with running a tap straight off the mains stopcock but it's a good idea.

After the stopcock it reduces to 10-11 l/m, up to 12l/m if running purely off of the cold mains.

any pics of the install?

 

[dblvkrb]

The water bouncing out the sink shouldn't have been affected by installing a pressure reducer as technically these restrict standing pressure, not working pressure (or at least thats my understanding of them). Basically the standing pressure of your system will be exactly the same as before you installed your new water main so you don't have anything to worry about regarding tap rating etc. I'd turn your pressure reducer up to max, then run the tap and slowly turn the valve down until you achieve your desired flow rate.

Well this is exactly my point, thank you! I've heard "pressure and flow are not the same things" about a hundred times, and I understand they are definitely not directly related, but you can't deny the flow was way too high if anything before installing the PRV.

Do you not think it would be risky to simply turn the valve down (increasing the pressure) until I have 15l/m? I know plenty of people who "overclock" their systems and don't have any issues for years, but then I've heard the other kind of story where it all goes wrong..

 

[dblvkrb]

Off the stop tap to the prv what size pipe

Also what size is the prv 15mm

Pipe size off the prv to the boiler ?

15mm for both - the distance from the stopcock to the boiler is maybe 3/4 metres.

 

[ShaunCorbs]

15mm for both - the distance from the stopcock to the boiler is maybe 3/4 metres.

you sure its not a 20mm main ?

what make of prv are you using

 

[Riley]

You will not increase the flow by increasing the pressure. If that’s what you’re intent on doing you might as well remove the PRV. The PRV could be defective. In terms of what does it reduce to I meant what pipesize is it coming out of the stopcock. Do you notice this reduced flow at all outlets

 

[dblvkrb]

any pics of the install?

Of the new mains, stopcock and PRV I assume? No, but I may go and take a look tomorrow and take some pics. I have a picture of the boiler setup (Alpha Flow Smart, 50l) if that would help at all.

 

[Riley]

What is the cold inlet and hot outlet on the boiler

 

[Riley]

Yes boiler pic

 

[dblvkrb]

you sure its not a 20mm main ?

what make of prv are you using

It's a newly installed 25mm main as I mentioned in my original post, I meant 15mm pipe running from the stopcock.

 

[dblvkrb]

You will not increase the flow by increasing the pressure. If that’s what you’re intent on doing you might as well remove the PRV. The PRV could be defective. In terms of what does it reduce to I meant what pipesize is it coming out of the stopcock. Do you notice this reduced flow at all outlets

15mm coming off the stopcock - the flow rate is the same on the 1st floor and in the loft conversion, almost no loss the further up the house you go.

It might be a defective PRV - would this definitely not reduce the flow rate if it were working effectively?

 

[Riley]

Honest opinion I’d be tempted to change the PRV

 

[dblvkrb]

Yes boiler pic

Not the greatest pic, but hopefully gives you an idea of the boiler - the hot flow is only 2 l/m less than off the cold mains, I doubt it is the issue.

 

[dblvkrb]

It's a newly installed 25mm main as I mentioned in my original post, I meant 15mm pipe running from the stopcock.

Also completely forgot make of PRV, will check though.

 

[dblvkrb]

As Riley and others have said pressure and flow are not the same thing. A PRV could have sorted out the splashing tap but will not have affected flow.

As an example:

If we have two taps both with a flow rate of 15 lpm where tap no1 has 6bar pressure and tap no2 has 3 bar pressure, both will fill the sink up in the same amount of time. But when taps are turned on tap no1 will splash much more violently off the surface of the sink due to the much greater pressure than tap no2. i.e. its the same amount of water but coming out with more force, turn the pressure down and water hits the sink with less force so doesn't splash/bounce but its exact same amount of water per minute hitting the sink.

I understand this, and I'll caveat by saying I didn't personally test the flow rate before the PRV installation but it's obvious it has reduced both the flow rate and the pressure. I'm guessing where we may be getting to is possibly a defective/clogged PRV?

 

[Aire]

As much as i appreciate why everyone is saying increasing the pressure of the prv won't do anything, turning it up and seeing if it improves isn't going to hurt, even by half a bar, the boiler is rated up to 5bar anyway so it's not going to hurt. And if it doesn't work atleast you've ruled it out.

 

[rpm]

Seen 6bar static pressure reduce to 0.6bar dynamic pressure along with the sort of flow you would expect from 0.6bar.

 

[rpm]

Not the greatest pic, but hopefully gives you an idea of the boiler - the hot flow is only 2 l/m less than off the cold mains, I doubt it is the issue.

View attachment 36032

Not the greatest pic, but hopefully gives you an idea of the boiler - the hot flow is only 2 l/m less than off the cold mains, I doubt it is the issue.

View attachment 36032

Not the greatest pic, but hopefully gives you an idea of the boiler - the hot flow is only 2 l/m less than off the cold mains, I doubt it is the issue.

View attachment 36032

Those valves supposed to be closed guys?

 

[dblvkrb]

Those valves supposed to be closed guys?

So.. I could test increasing the static (PRV) pressure to see if the dynamic pressure improves the flow, have I understood this right?

I'll pass on whether the valves should be closed (I did not install the boiler) - but it is working as expected and the hot flow is similar to the cold mains flow.

 

[Aire]

Yes you can increase the pressure, as I said your boiler is rated at 5 bar, stick below that and you'll be fine.

And no those valves aren't supposed to be closed, but then the hot feed coming from the top of the heat store should also feed the boiler through a blending valve mixed with the cold main. Whoever installed the boiler hasn't finished it.

 

[Riley]

If that’s a heat store then what pressure is that safe up to??

 

[dblvkrb]

Yes you can increase the pressure, as I said your boiler is rated at 5 bar, stick below that and you'll be fine.

And no those valves aren't supposed to be closed, but then the hot feed coming from the top of the heat store should also feed the boiler through a blending valve mixed with the cold main. Whoever installed the boiler hasn't finished it.

Thanks - I will definitely check out the boiler setup with the installer, the blending valve should be somewhere. The boiler is rated to 5 bar, just worried about the taps being rated to 3, but I think I may have to test this anyway to see exactly how much the flow rate is effected.

 

[Riley]

Dear lord why risk leaks and damage swap out the prv also what is the cold inlet pipe size to the hot water Store.

 

[Riley]

My suspicion is it’s a piping issue exacerbated by the restriction of a prv

 

[Riley]

Seriously though test it in various places you’re plunging straight in with what isn’t the answer and will not be told

 

[Aire]

If that’s a heat store then what pressure is that safe up to??

It's rated upto 5 bar, the boiler, flue gas recovery and heat store all come together. The heat store is pressurised by the heating water not the mains, it has a coil going through it which comes off the flue gas and back into the cold feed to the boiler, at least it should do but as I said, it's not finished. And I just want to point out to you again that I don't disagree with anything your saying and op has gone the wrong way about reducing his flow rate but for the sake of adjusting the pressure and how long it will take it's worth a try.

 

[Riley]

But it’s not answering the issue it’s a bodge

 

[Riley]

So what feeds the store??? Surely it’s mains water?

 

[dblvkrb]

Seriously though test it in various places you’re plunging straight in with what isn’t the answer and will not be told

What would you test first? If it isn't the PRV what do you think the issue is? The pipes were tested and cleaned prior to installation.

 

[dblvkrb]

It's rated upto 5 bar, the boiler, flue gas recovery and heat store all come together. The heat store is pressurised by the heating water not the mains, it has a coil going through it which comes off the flue gas and back into the cold feed to the boiler, at least it should do but as I said, it's not finished. And I just want to point out to you again that I don't disagree with anything your saying and op has gone the wrong way about reducing his flow rate but for the sake of adjusting the pressure and how long it will take it's worth a try.

Just want to add that the picture uploaded was about a month ago and probably was mid installation, but I am definitely going to double check it (and take some more pics).

 

[Aire]

So what feeds the store??? Surely it’s mains water?

 

[Aire]

What would you test first? If it isn't the PRV what do you think the issue is? The pipes were tested and cleaned prior to installation.

Take a picture of the stop tap and pressure reducing valve.

 

[Aire]

To be honest, I know we're going off track here but the whole system seems pointless to me, why run cold mains through heat recovery, then through a heat store only to blend it down to 30°. Why not just have the heat recovery?

 

[Riley]

Sorry im with you it’s a set ok that makes more sense but my argument still remains. I’m not arguing with the logic of what you’re saying but that still looks like it’s piped in 22 under the boiler for cold and dhw and op has said it comes in in 15mm so obviously it upsized too which is going to further affect flow

 

[Aire]

Hard to tell, the shock arrestor under the boiler looks to me like it's piped on a 15mm supply.

 

[Riley]

Not the tidiest install is it 🙂

 

[Aire]

Not the tidiest install is it 🙂

Haha, nope. That we can agree on 😉

 

[king of pipes]

Personally I think the install is a bit untidy the flow rate could be improved on by correct pipe sizing is there a dedicated supply straight from the incoming stopcock purely supplying the cold water inlet to the gas saver 22mm minimum without anything else coming off it? there will be Pressure loss as water passes through each piece of equipment and height and length of the pipework needs to be considered. Kop

 

[dblvkrb]

Personally I think the install is a bit untidy the flow rate could be improved on by correct pipe sizing is there a dedicated supply straight from the incoming stopcock purely supplying the cold water inlet to the gas saver 22mm minimum without anything else coming off it? there will be Pressure loss as water passes through each piece of equipment and height and length of the pipework needs to be considered. Kop

I will double check and hopefully take some more pictures, but I think it's 15mm supply in for the cold water inlet. Thanks all for your advice so far - very useful.

 

[fezster]

I'm surprised by some of the responses relating to pressure and flow rate.

The pipe diameter and length determine the pressure loss in the pipe run. If you have a longer pipe (you can try this with a garden hose reel), the pressure loss will be greater and you will get less flow at the end. If you increase the pipe diameter, the pressure loss will be less and you will get more flow (EDIT to clarify - "more" than the previous example - you can't get more out than you put in!).

Given you will have a loss of pressure along the pipe run, if you increase the pressure you start with, the resulting working pressure (i.e. with water flowing) will be higher too. Therefore, increasing the pressure on the PRV (assuming your incoming pressure is sufficient) will indeed result in a higher flow rate.

I do agree that the more correct approach would be to size the pipes adequately in the first place. You also need to ensure that the pressure is sufficiently reduced to avoid damage to components (eg. some thermostatic showers are designed to work at 3 bar).

 

[Welder]

Can someone please explain to me why plumbers do not understand how flow is a consquence of pressure & bore? Keep the bore the same & increase the pressure & flow increases. Similarly, increase the bore & keep. Pressure the same & flow increases.

The point of a pressure reducing valve is to provide a maximum pressure with 'unduly' limiting flow. All PRVs impeed flow somewhat.

In terms of increasing flow in this instance 'bouncing out of the sink' is zero indication of anything. The only real test is a weir gauge or physically timed test. The real test is looking at the flow rate of a second outlet.

I hope this basic information helps people.

 

[Rob Foster]

Also going above 3bar can impact other things such as the boiler from a safety perspective

I agree this is the most worrying aspect of this idea
Centralheatking

 

[Rob Foster]

Can someone please explain to me why plumbers do not understand how flow is a consquence of pressure & bore? Keep the bore the same & increase the pressure & flow increases. Similarly, increase the bore & keep. Pressure the same & flow increases.

The point of a pressure reducing valve is to provide a maximum pressure with 'unduly' limiting flow. All PRVs impeed flow somewhat.

In terms of increasing flow in this instance 'bouncing out of the sink' is zero indication of anything. The only real test is a weir gauge or physically timed test. The real test is looking at the flow rate of a second outlet.

I hope this basic information helps people.

Pressure and volume are obviously inter related but in actual fact separate issues , in fact Yorkshire Dave if you pm me we could produce a simple fact sheet to clear up,this issue
Once and for all ...ok ?
Centralheatking

 

[John.g]

Increasing the pressure will certainly increase flow rate as it is proportional to the sq.root of pressure, if the pressure is increased to 4 bar at the tap (by adjusting the pressure reducing valve) then the flow rate should theoretically increase by a factor of (4/3)^0.5 = 1.15 so the flow rate should increase from 10 to 11.5 lpm.....that is assuming there is 3 bar at the tap when it was flowing 10 lpm originally, in practice pipe friction losses will reduce this.

Pressure and flow are two different things, upping the pressure reducer to 4bar will likely have no impact on the flow rate.

 

[Welder]

Increasing the pressure will certainly increase flow rate as it is proportional to the sq.root of pressure, if the pressure is increased to 4 bar at the tap (by adjusting the pressure reducing valve) then the flow rate should theoretically increase by a factor of (4/3)^0.5 = 1.15 so the flow rate should increase from 10 to 11.5 lpm...that is assuming there is 3 bar at the tap when it was flowing 10 lpm originally, in practice pipe friction losses will reduce this.

Personally, I'd be ensuring all valves are fully open and no undue or inadvertant restrictions are being applied to throttle flow before messing with what are specific design settings.

 

[Riley]

I just think they need to get a plumber in that understands system design to test all facets correctly

 

[Chuck]

Can someone please explain to me why plumbers do not understand how flow is a consequence of pressure & bore?

All NVQ-qualified plumbers understand (or once understood!) these ideas, which are part of the Level 1 one curriculum, e.g.:

https://bpec.org.uk/wp-content/uplo...2-and-L3-Plumbing-and-Heating-Diploma-v23.pdf

One problem is that not everybody who does plumbing is a qualified plumber. Also, customers use 'water pressure' in a colloquial, not a technical sense. When lay-persons talk about water pressure they are usually referring to the properties of the jet formed at outlets and how the jet and flow respond to small changes in the control rather than what's going on inside the pipework.

 

[dblvkrb]

Update:

Ok so I've taken a picture of the PRV (attached), the pipe from the stopcock is definitely 22mm, not 15mm, my bad.

I couldn't get to the boiler today as the house is a building site at the moment and the garage (where the boiler is located) is all boarded up. That being said I could see the the pipes are all housed now, so I suspect the blending valve is fitted but I will check next week.

The boiler is rated to 5 bar, but I was thinking of testing the pressure at each of the taps using a gauge, before testing to see if there if is an increase in flow rate when going up in .5 increments (pressure) each time.

Thoughts?

 

[Riley]

Cut into the pipework and test straight above the PRV in the first instance. LPM and obviously static pressure

 

[Mike wareham]

Run the tap at 10l/min and then check the pressure guage

 

[Mike wareham]

Then at 5l/min and check the pressure guage

 

[Mark K]

Can someone please explain to me why plumbers do not understand how flow is a consquence of pressure & bore? Keep the bore the same & increase the pressure & flow increases. Similarly, increase the bore & keep. Pressure the same & flow increases.

The point of a pressure reducing valve is to provide a maximum pressure with 'unduly' limiting flow. All PRVs impeed flow somewhat.

In terms of increasing flow in this instance 'bouncing out of the sink' is zero indication of anything. The only real test is a weir gauge or physically timed test. The real test is looking at the flow rate of a second outlet.

I hope this basic information helps people.

Agreed, a restrictive PRV will allow the pressure to build while there is no use, but not allow enough flow to "replenish" that pressure when there is a draw.

A 15mm supply and PRV could get a 6" main in a factory up to pressure given time, but obviously could not flow enough to cope with a 6" valve being opened.

Flow measurement at the tap and pressure readings before and after the PRV and just before the tap while it's running would help identify the issue. i.e. incoming pressure not maintained, pressure not maintained through the PRV or pressure loss in the system to the tap. Obviously, the rated pressure at the tap maintains the flow through it to atmosphere.

 

[64degrees]

If you want maxperformance from your combi give it a dedicated ( first tee from incoming main) 22 mm feed and distribute the hot water to the first outlet in 22mm pipe. There’s a flow restrictor in the boiler, but if you give all the water it should perform as per manufacturers specs - unless they maybe talk them up a bit? Didn’t read the whole the thread, think you mentioned a combi store I would have fitted an Atag

 

[dan_the_plumber]

Also going above 3bar can impact other things such as the boiler from a safety perspective

Hi Riley. Sorry are we talking about the heating or DHW circuit here?

 

[Riley]

As it’s a stored combi then I’m guessing it doesn’t matter. I was equally confused

 

[Old Account]

No never , you might well be creating a pressurised bomb
Combi set ups operate at 1.5 bar
And no more ever. There have been accidents ! With over over pressurised unvented systems
I know it’s my specialist area
Centralheatking

What bomb are you talking about mate? In Europe we have 5 bar mains incoming cold water and have combi boilers installed never encounter any time bomb hahaha don’t get your point to be fair

 

[Riley]

Are they not reduced before entering appliance though?

 

[dblvkrb]

Small update:

Static pressure is 4 bar, dynamic pressure (read from PRV at mains) is 2.4 bar when 1 tap is running and 1.5 bar with 2 taps running. Is this normal?

I still intend to dial up the static pressure and test the flow with a Weir gauge, but likely won't be able to test for a week or so.

 

[John.g]

Small update:

Static pressure is 4 bar, dynamic pressure (read from PRV at mains) is 2.4 bar when 1 tap is running and 1.5 bar with 2 taps running. Is this normal?

I still intend to dial up the static pressure and test the flow with a Weir gauge, but likely won't be able to test for a week or so.

You would need to take some more readings as Mark K suggested.
In the very first post you said that you renewed the old lead piping in 25 mm and that you then installed a PRV because the pressure was/is too high. Assuming the mains pressure hasn't changed then the static head (without PRV) will be exactly the same as before so no danger of over pressures in the combi as it will be rated for a maximum static pressure?, so why not remove the PRV and fit simple restrictors to your taps or just don't open them fully.
For interest only, I have 2 x 1/2 ins kitchen taps, one flows 10 LPM from a static mains pressure of ~ 2.5/2.8 bar at the tap, the other flows 5 LPM from the attic tank with a static head of ~ 0.6 bar.

 

[dblvkrb]

I know more tests need to be run and I will run them and report back.

I agree we could run the mains at full pressure and put restrictors on at each outlet, but I believe the plumber has gone the other way around by simply reducing all incoming pressure, which isn't ideal.

 

[Mike wareham]

Small update:

Static pressure is 4 bar, dynamic pressure (read from PRV at mains) is 2.4 bar when 1 tap is running and 1.5 bar with 2 taps running. Is this normal?

I still intend to dial up the static pressure and test the flow with a Weir gauge, but likely won't be able to test for a week or so.

 

[Mike wareham]

How long is the new leingth of 25mm plastic pipe? does it go to to a stoptap in the path or road? Is this stoptap turned on fully? sounds to me like there is a restriction somewhere, the new PRV in the house has a filter is this clean, you also have a stoptap in the house is this blocked with debris,as pressure is droping when there is a greater demand

 

[dblvkrb]

How long is the new leingth of 25mm plastic pipe? does it go to to a stoptap in the path or road? Is this stoptap turned on fully? sounds to me like there is a restriction somewhere, the new PRV in the house has a filter is this clean, you also have a stoptap in the house is this blocked with debris,as pressure is droping when there is a greater demand

25mm pipe is maybe 4 meters long, yes it does go to a stop tap in the road which is fully open, the stopcock in the house is fully open.

Why do you think there is debris - should I not be losing as much pressure when opening a tap/2 taps from mains pressure?

 

[Mike wareham]

25mm pipe is maybe 4 meters long, yes it does go to a stop tap in the road which is fully open, the stopcock in the house is fully open.

Why do you think there is debris - should I not be losing as much pressure when opening a tap/2 taps from mains pressure?

I would expect about 20l/min from the kitchen cold tap at that pressure,and if the mains pipe from the road is only 4M away not a great deal of flow would be lost, does your new 25mm pipe go to the main in the road or is it joined to the exhisting smaller diameter pipe somewhere, ( was it connected by the water company) ?

 

[Mike wareham]

I would expect about 20l/min from the kitchen cold tap at that pressure,and if the mains pipe from the road is only 4M away not a great deal of flow would be lost, does your new 25mm pipe go to the main in the road or is it joined to the exhisting smaller diameter pipe somewhere, ( was it connected by the water company) ?

Is it a shared supply that feeds other houses?

 

[John.g]

I would expect about 20l/min from the kitchen cold tap at that pressure,and if the mains pipe from the road is only 4M away not a great deal of flow would be lost, does your new 25mm pipe go to the main in the road or is it joined to the exhisting smaller diameter pipe somewhere, ( was it connected by the water company) ?

I seem to remember that my kitchen taps have a flow coefficient (Kvs) of something like 0.4 M3/h @ 1 bar which equates to 6.7 LPM @ 1 bar, if the OPs taps are similar then it would require 5 bar to get his expected 15 LPM, his reading of 2.4 bar (one tap) would suggest a flow rate of ~ 10.4 LPM (easy to measure this with a empty milk bottle) the 1.5 bar reading (two taps) would suggest a combined flow rate of ~ 16.4 LPM. The PRV will have its own Kvs which affects flow rate as well plus the differential pressure across it will have a big effect on its output. This Kvs is not known but the manufacturers should certainly know it.
I would suggest (as has been suggested in other posts) increasing the PRV outlet pressure to max with both taps open and then measure both tap flow rates, I would also suggest cleaning the PRV strainer if only to rule it out.
Depending on the above test, to really narrow down the problem I would replace (temporarily) the PRV with a spool piece and repeat the measurements, that will tell a lot IMO.

 

[dblvkrb]

Is it a shared supply that feeds other houses?

The 25mm pipe goes directly to the mains (someone from the water board did the job). It is not a shared supply.

 

[dblvkrb]

I seem to remember that my kitchen taps have a flow coefficient (Kvs) of something like 0.4 M3/h @ 1 bar which equates to 6.7 LPM @ 1 bar, if the OPs taps are similar then it would require 5 bar to get his expected 15 LPM, his reading of 2.4 bar (one tap) would suggest a flow rate of ~ 10.4 LPM (easy to measure this with a empty milk bottle) the 1.5 bar reading (two taps) would suggest a combined flow rate of ~ 16.4 LPM. The PRV will have its own Kvs which affects flow rate as well plus the differential pressure across it will have a big effect on its output. This Kvs is not known but the manufacturers should certainly know it.
I would suggest (as has been suggested in other posts) increasing the PRV outlet pressure to max with both taps open and then measure both tap flow rates, I would also suggest cleaning the PRV strainer if only to rule it out.
Depending on the above test, to really narrow down the problem I would replace (temporarily) the PRV with a spool piece and repeat the measurements, that will tell a lot IMO.

This is interesting, I thought the indoor tap nozzles would be restricting flow in some manner despite there not being separate flow restrictors in place and I have readings similar to yours on the l/m side. Though I haven't measured it yet, I believe the garden tap is putting out more l/m.

100% agree with you and others who have mentioned I need to test by increasing the pressure or replacing the PRV (or both), hopefully I can get the plumber in this week to talk through and test.

 

[dblvkrb]

Conclusion..

We tested the garden tap and it was putting out >20 l/m, the plumber explained that it is the 12mm flexi pipes that came with the tap sets are restricting the flow a great deal. We tested some of the shower taps with and without the nozzles attached and we measured a difference of about 3-4 l/m (going up to 16 l/m).

That being said the plumbing of the boiler wasn't completely finished, with the blending valve being installed a couple of weeks back. The results are a bit odd. Most of the taps still output at 10-12 l/m, however, the bath taps output at near 20l/m with both taps fully open, the shower output is at 16/m which is certainly good enough for what we need.

I'm not sure why there is such variance but it's worked out for the best, I can only assume it's the type of connections used for each tap combined with the fact that the boiler is now a great deal more efficient now that the blending valve is in. We're still at 4 bar of standing pressure.

 

[John.g]

Conclusion..

We tested the garden tap and it was putting out >20 l/m, the plumber explained that it is the 12mm flexi pipes that came with the tap sets are restricting the flow a great deal. We tested some of the shower taps with and without the nozzles attached and we measured a difference of about 3-4 l/m (going up to 16 l/m).

That being said the plumbing of the boiler wasn't completely finished, with the blending valve being installed a couple of weeks back. The results are a bit odd. Most of the taps still output at 10-12 l/m, however, the bath taps output at near 20l/m with both taps fully open, the shower output is at 16/m which is certainly good enough for what we need.

I'm not sure why there is such variance but it's worked out for the best, I can only assume it's the type of connections used for each tap combined with the fact that the boiler is now a great deal more efficient now that the blending valve is in. We're still at 4 bar of standing pressure.

Shower heads are designed to give a nice spray effect so there is a considerable pressure drop across them so no really big surprises there. You are getting 20 LPM from a bath tap and 10 LPM from the other taps, my bath taps are 3/4", all the remaining taps are ~ 1/2"or even less (metric), my upstairs bath tap flows 12 LPM @ gravity head of 0.25/0.3M, the upstairs bathroom basin tap flows ~ 4 LPM @ the same head.

All in All I think you should be happy enough.

Did you observe the PRV pressure with a flow rate of say 20 LPM?, even assuming a mains PRV upstream pressure of 6/8 bar one would expect a "drooping" in the PRV pressure of (depending on its type & quality) 0.25 bar to 0.5 bar giving 3.75/3.5 bar? @ 20 LPM.

 

[dblvkrb]

Shower heads are designed to give a nice spray effect so there is a considerable pressure drop across them so no really big surprises there. You are getting 20 LPM from a bath tap and 10 LPM from the other taps, my bath taps are 3/4", all the remaining taps are ~ 1/2"or even less (metric), my upstairs bath tap flows 12 LPM @ gravity head of 0.25/0.3M, the upstairs bathroom basin tap flows ~ 4 LPM @ the same head.

All in All I think you should be happy enough.

Did you observe the PRV pressure with a flow rate of say 20 LPM?, even assuming a mains PRV upstream pressure of 6/8 bar one would expect a "drooping" in the PRV pressure of (depending on its type & quality) 0.25 bar to 0.5 bar giving 3.75/3.5 bar? @ 20 LPM.

I haven't read the drop off since my last test - suspect it is going down to ~2bar with 20l/m coming out. The plumber was nervous about going up to 5 bar to test as the fittings are only rated to 3bar. I now see little value in testing an increase in pressure given the l/m had increased where needed.