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Hello Guys

I recently posted a thread about low water pressure at taps in a new kitchen installed by a company using sub-contractors. I have 0.44 bar of hot water pressure and am getting a flow rate of 4.5 Lpm at the new hot monobloc. The Blanco people say that the taps are rated at minimum 0.3 bar and that a 0.3 bar head should deliver 7.9 Lpm. At my 0.44 bar I should be getting 11.6 Lpm, over twice as much.

The Company are saying that 0.3 bar is the lowest pressure tap they use. That doesn’t seem to me to address the issue. Does it? The overhead supply mains water supply goes on a further 3 metres to supply the Utility Room monobloc (combined hot and cold flow-rate of 25 Lpm) and the central heating boiler. Yet the combined hot and cold flow rate in the new kitchen monobloc is 14.5 Lpm. It seems that both hot and cold are throttled back.

A clogged aerator has been identified as a possible problem and 15mm service valves are installed. Would ‘full-bore’ service valves help? Also is it possible to measure the flow rate at the tails of the pipework in both kitchen and utility as Company is saying the Utility monobloc could be a lower minimum bar rating.

Any advice in any of these areas will be gratefully received as the Kitchen Company are beginning to fade away with the final comment of “We don’t do taps of less than 0.3 bar” without offering further investigation.
 
Hello Guys

I recently posted a thread about low water pressure at taps in a new kitchen installed by a company using sub-contractors. I have 0.44 bar of hot water pressure and am getting a flow rate of 4.5 Lpm at the new hot monobloc. The Blanco people say that the taps are rated at minimum 0.3 bar and that a 0.3 bar head should deliver 7.9 Lpm. At my 0.44 bar I should be getting 11.6 Lpm, over twice as much.

The Company are saying that 0.3 bar is the lowest pressure tap they use. That doesn’t seem to me to address the issue. Does it? The overhead supply mains water supply goes on a further 3 metres to supply the Utility Room monobloc (combined hot and cold flow-rate of 25 Lpm) and the central heating boiler. Yet the combined hot and cold flow rate in the new kitchen monobloc is 14.5 Lpm. It seems that both hot and cold are throttled back.

A clogged aerator has been identified as a possible problem and 15mm service valves are installed. Would ‘full-bore’ service valves help? Also is it possible to measure the flow rate at the tails of the pipework in both kitchen and utility as Company is saying the Utility monobloc could be a lower minimum bar rating.

Any advice in any of these areas will be gratefully received as the Kitchen Company are beginning to fade away with the final comment of “We don’t do taps of less than 0.3 bar” without offering further investigation.
Update. The Company are saying that the tap manufacturers report a combined hot and cold flow rate of 7.9 Lpm for their 0.3 min pressure taps. I am getting 14.5 Lpm combined and the implication is that I should be happy with that. But surely that figure of 7.9 Lpm combined flow-rate must be when both hot AND cold are at 0.3 bar. My pressures are hot 0.44 bar and cold (guesstimate) 1.5 bar. Is it even possible to get a flow-rate of 7.9 Lpm at those pressures at 0.3 min bar taps?
 
Have you considered loss of head due to flow?

Many things can reduce the working head/pressure. Examples include limescale in connections to the cylinder, long runs of 15mm pipe, traditional stopcocks, and narrow-bore isolation valves. Gate valves and full bore isolation valves do not. That 0.3 bar Blanco is discussing will be the working pressure, not the standing pressure.

You might have 0.5bar standing head (I think you said your cistern is 5 m above the tap) but that pressure will drop when you open the tap. Probably the tap is rated at 0.3bar working head. This is the pressure you would see at a manometer installed on the pipework immediately before the tap with the tap open and therefore very different from the standing pressure.

Also is it possible to measure the flow rate at the tails of the pipework in both kitchen and utility as Company is saying the Utility monobloc could be a lower minimum bar rating.
If you have a water meter, it is very easy to measure flow. Check nothing is flowing first, and then open the relevant tap and see how fast the numbers go round. But as the flow into the tap must equal precisely the flow out of the tap, the bucket method you have presumably used up to now should suffice.

But surely that figure of 7.9 Lpm combined flow-rate must be when both hot AND cold are at 0.3 bar.
Agreed.

Is it even possible to get a flow-rate of 7.9 Lpm at those pressures at 0.3 min bar taps?
Hard to say. The manufacturer may be basing the flow on a 67% hot, 33% cold mix. As the relationship between flow and pressure is non-linear, it is hard to say what the tap will do with mixed pressures, particularly if it is a thermostatic mixer. At a guess, I'd suggest the tap flow would = half of the stated combined flow at the higher pressure + half of the stated combined flow at the lower pressure. That said, if we do not know the actual woking pressures (as above) then this is a bit hypothetical.
 
Have you considered loss of head due to flow?

Many things can reduce the working head/pressure. Examples include limescale in connections to the cylinder, long runs of 15mm pipe, traditional stopcocks, and narrow-bore isolation valves. Gate valves and full bore isolation valves do not. That 0.3 bar Blanco is discussing will be the working pressure, not the standing pressure.

You might have 0.5bar standing head (I think you said your cistern is 5 m above the tap) but that pressure will drop when you open the tap. Probably the tap is rated at 0.3bar working head. This is the pressure you would see at a manometer installed on the pipework immediately before the tap with the tap open and therefore very different from the standing pressure.


If you have a water meter, it is very easy to measure flow. Check nothing is flowing first, and then open the relevant tap and see how fast the numbers go round. But as the flow into the tap must equal precisely the flow out of the tap, the bucket method you have presumably used up to now should suffice.


Agreed.


Hard to say. The manufacturer may be basing the flow on a 67% hot, 33% cold mix. As the relationship between flow and pressure is non-linear, it is hard to say what the tap will do with mixed pressures, particularly if it is a thermostatic mixer. At a guess, I'd suggest the tap flow would = half of the stated combined flow at the higher pressure + half of the stated combined flow at the lower pressure. That said, if we do not know the actual woking pressures (as above) then this is a bit hypothetical.
That information has been really helpful Ric2013, particularly the confirmation that his 7.9 Lpm from Blanco must be based on a head of 0.3 bar for both hot AND cold and that the company can not therefore rest on that as an expectation as I have 0.44 and Mains pressure (estimate 1.5 to 2.0 bar).

The taps are not thermostatic but I see your point about how Blanco might configure the mix.

The (actually very good) company are going to fit full-bore service valves to replace the standard service valves.

Much obliged.
 
How have you measured or calculated 0.44 bar?
Hi Ric2013

I added together the following measurements:

tap outlet to ground floor ceiling - first storey floor to ceiling - loft joists to bottom ow CW tank. I then added in 10cm for first-floor ceiling void and a further 17cm for ground-floor ceiling void (inc plasterboard and floor decking. I came out with approx 4.41m

MDLJK
 
Update. The Company are saying that the tap manufacturers report a combined hot and cold flow rate of 7.9 Lpm for their 0.3 min pressure taps. I am getting 14.5 Lpm combined and the implication is that I should be happy with that. But surely that figure of 7.9 Lpm combined flow-rate must be when both hot AND cold are at 0.3 bar. My pressures are hot 0.44 bar and cold (guesstimate) 1.5 bar. Is it even possible to get a flow-rate of 7.9 Lpm at those pressures at 0.3 min bar taps?
Just bear in mind that flow is proportional to the sq.root of pressure so the increase in flow at 0.44bar from 0.3bar is a by a factor of 1.21 and not 1.47.
One would think that valves that have internal mixing (either thermostatic or manual) would tend to mix at the lower pressure, or possibly like explained in post #3 above, you might just set your mixer to your normal temperature, measure the individual flowrates with hot/cold isolated, add them and compare it with your actual combined flow and that will give a interesting comparison.
 
Hi Ric2013

I added together the following measurements:

tap outlet to ground floor ceiling - first storey floor to ceiling - loft joists to bottom ow CW tank. I then added in 10cm for first-floor ceiling void and a further 17cm for ground-floor ceiling void (inc plasterboard and floor decking. I came out with approx 4.41m

MDLJK
Grand. Yes, that's your standing pressure, not your working pressure.

It's occurred to me that you could get an idea how much resistance there is in the pipework by seeing what happens if you try to run your kitchen tap at the same time as your utility room tap. From your previous comments, I suspect the loss of head (difference between standing and working pressures) may not be much, but if you run, say 5 lpm from your utility room tap and the kitchen tap almost ceases to flow, that would tend to indictate that there is a restriction in the pipework.
 
Grand. Yes, that's your standing pressure, not your working pressure.

It's occurred to me that you could get an idea how much resistance there is in the pipework by seeing what happens if you try to run your kitchen tap at the same time as your utility room tap. From your previous comments, I suspect the loss of head (difference between standing and working pressures) may not be much, but if you run, say 5 lpm from your utility room tap and the kitchen tap almost ceases to flow, that would tend to indictate that there is a restriction in the pipework.
Hi. I tried this and bringing on the Utility Room hot water did not seem to greatly effect the flow rate of the kitchen hot water. Kitchen is 4.0 Lpm Utility is 7.5 Lpm. The new kitchen install was done completely in plastic apart from final part for service valves etc. Plumber tee-d off supply in loft (single storey offshoot) took it down then wall, along wall before rising up. He has taken the horizontal run ‘back’ along the direction of flow in loft above which did disappoint me but it has to be no more than 1.2m/4 ft. So thanks for this. You’ve proven that the new pipework is not restricted.
 
Just bear in mind that flow is proportional to the sq.root of pressure so the increase in flow at 0.44bar from 0.3bar is a by a factor of 1.21 and not 1.47.
One would think that valves that have internal mixing (either thermostatic or manual) would tend to mix at the lower pressure, or possibly like explained in post #3 above, you might just set your mixer to your normal temperature, measure the individual flowrates with hot/cold isolated, add them and compare it with your actual combined flow and that will give a interesting comparison.
Weird - separately hot is 4Lpm and cold is 12Lpm. Combined DOES NOT give 16 Lpm as might be expected but rather it gives 9.5 Lpm. How can that happen?
 
Don't know really but assuming hot water at 60C, cold at 10C and mixed at 40C then the mix is 0.6hot to 0.4cold = 5.7hot & 3.8cold (9.5 LPM), so available cold is almost all used as expected and the hot is throttled to give 5.7 LPM but strange that it flows 12 LPM while still in the throttled state with just the back pressure of the cold removed, assuming tested in this manner.
 
Don't know really but assuming hot water at 60C, cold at 10C and mixed at 40C then the mix is 0.6hot to 0.4cold = 5.7hot & 3.8cold (9.5 LPM), so available cold is almost all used as expected and the hot is throttled to give 5.7 LPM but strange that it flows 12 LPM while still in the throttled state with just the back pressure of the cold removed, assuming tested in this manner.
Hi John g

so I tested hot alone - 4.0 Lpm (0.4 bar head) Cold 12 Lpm (mains pressure) and when both were on together it was 9.5 Lpm. Was that the method you expected?
 
Hi. I tried this and bringing on the Utility Room hot water did not seem to greatly effect the flow rate of the kitchen hot water. Kitchen is 4.0 Lpm Utility is 7.5 Lpm. The new kitchen install was done completely in plastic apart from final part for service valves etc. Plumber tee-d off supply in loft (single storey offshoot) took it down then wall, along wall before rising up. He has taken the horizontal run ‘back’ along the direction of flow in loft above which did disappoint me but it has to be no more than 1.2m/4 ft. So thanks for this. You’ve proven that the new pipework is not restricted.
Can yous sketch us the pipework arrangement? I've done a sketch of how I assumed it was, based on your initial post, but sounds like I got the wrong impression. Apologies for frankly appalling sketch (and appreciate I've shown hot and cold taps as separate for diagramatic purposes: I am aware what you have are mixers). Nuova immagine bitmap.jpg
 
Don't know really but assuming hot water at 60C, cold at 10C and mixed at 40C then the mix is 0.6hot to 0.4cold = 5.7hot & 3.8cold (9.5 LPM), so available cold is almost all used as expected and the hot is throttled to give 5.7 LPM but strange that it flows 12 LPM while still in the throttled state with just the back pressure of the cold removed, assuming tested in this manner.
By throttled state, do you mean the mixer is still set to give a mix of waters, and the cold has been isolated at the isolator? I wonder if this is what mdljk did?

Question: does this tap have separate controls for hot and cold, or, as I assume, is it a single lever mixer?
 
Can yous sketch us the pipework arrangement? I've done a sketch of how I assumed it was, based on your initial post, but sounds like I got the wrong impression. Apologies for frankly appalling sketch (and appreciate I've shown hot and cold taps as separate for diagramatic purposes: I am aware what you have are mixers).View attachment 60349
F381C23C-BF63-4F2D-B091-F05D90DA7545.jpeg
 
By throttled state, do you mean the mixer is still set to give a mix of waters, and the cold has been isolated at the isolator? I wonder if this is what mdljk did?

Question: does this tap have separate controls for hot and cold, or, as I assume, is it a single lever mixer?
Yes, that's what I mean, leave the mixer in its mixed position and isolate each supply separately. I have a very simple mixer using two hoses connected via a "Y" to a hand held shower head for dog washing, hot is gravity fed and cold ~ 2 bar mains and the hot flowrate is very close to its full flow rate rate, I leave the hot tap full open and just throttle the cold, the throttled cold is then practically the same with hot isolated as the calculated volume.
 
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Just bear in mind that flow is proportional to the sq.root of pressure so the increase in flow at 0.44bar from 0.3bar is a by a factor of 1.21 and not 1.47.
One would think that valves that have internal mixing (either thermostatic or manual) would tend to mix at the lower pressure, or possibly like explained in post #3 above, you might just set your mixer to your normal temperature, measure the individual flowrates with hot/cold isolated, add them and compare it with your actual combined flow and that will give a interesting comparison.
I just want to recap. The OP has 12l/m cold (which is acceptable) and 4l/m hot (not awful for a kitchen mixer, but definitely on the low side of acceptability and may not even comply with the Water Regulations requirement to have 50°C water available at the tap within 30 seconds (depending on how much dead-leg there is in the pipe run)).

If I assume 1.5 Bar cold working pressure and 1.44 Bar hot working pressure and use your pressure/flow equation above, and assume the mix the manufacturer suggests is 50/50, then I get 16 point something l/m combined flow, which is not far off the 14.5 l/m measured flow. Since the working pressure of the hot is certain to be at least slightly less than the 1.44 Bar (which is the standing pressure), but not massively less, I can't see that there is anything to suggest that the tap itself is defective.

I'm going to assume this is a lever mixer and that Mdljk has tested the hot and cold flows not as John wanted, but by putting the lever to fully hot and fully cold positions. If so, I would explain the fact that the combined flow is less than the sum of the fully hot and fully cold flows by the fact the this kind of mixer design tends to throttle both sides to some degree when in mixing mode and only opens the individual ports fully when in 100% cold or 100% hot mode. Presumably this is to ensure that (on balanced pressures), the flow is roughly consistent across the entire sweep of the hot-cold spectrum.

Back to where this leaves the OP: If (1.) the tap incorporates single or double check (anti-backflow) valves (or similar device - may be worth asking Blanco) or these have been fitted to both the pipes below the tap and (2.) with the dead leg from the cylinder to the tap fully cold (eg. first thing in the morning), the hot water reaches the tap in under 30 seconds (tap fully opened in 100% hot mode) and (3.) Blanco does not specifically state that the tap MUST be installed on a 'balanced pressure' (i.e. equal hot and cold pressures) system, I suggest the installation is acceptable from a technical point of view and if Mdljk wants better performance, this needs to be an 'extra'. On the other hand, if these 3 requirements have not been met, then the tap is not suited to the plumbing system at the house, the installation is illegal under the Water Supply (Water Fittings) Regulations 1999, and either the plumbing system needs to be modified or the tap needs to be replaced with one suitable for use with a traditional British mains cold, gravity hot system.
 
I just want to recap. The OP has 12l/m cold (which is acceptable) and 4l/m hot (not awful for a kitchen mixer, but definitely on the low side of acceptability and may not even comply with the Water Regulations requirement to have 50°C water available at the tap within 30 seconds (depending on how much dead-leg there is in the pipe run)).

If I assume 1.5 Bar cold working pressure and 1.44 Bar hot working pressure and use your pressure/flow equation above, and assume the mix the manufacturer suggests is 50/50, then I get 16 point something l/m combined flow, which is not far off the 14.5 l/m measured flow. Since the working pressure of the hot is certain to be at least slightly less than the 1.44 Bar (which is the standing pressure), but not massively less, I can't see that there is anything to suggest that the tap itself is defective.

I'm going to assume this is a lever mixer and that Mdljk has tested the hot and cold flows not as John wanted, but by putting the lever to fully hot and fully cold positions. If so, I would explain the fact that the combined flow is less than the sum of the fully hot and fully cold flows by the fact the this kind of mixer design tends to throttle both sides to some degree when in mixing mode and only opens the individual ports fully when in 100% cold or 100% hot mode. Presumably this is to ensure that (on balanced pressures), the flow is roughly consistent across the entire sweep of the hot-cold spectrum.

Back to where this leaves the OP: If (1.) the tap incorporates single or double check (anti-backflow) valves (or similar device - may be worth asking Blanco) or these have been fitted to both the pipes below the tap and (2.) with the dead leg from the cylinder to the tap fully cold (eg. first thing in the morning), the hot water reaches the tap in under 30 seconds (tap fully opened in 100% hot mode) and (3.) Blanco does not specifically state that the tap MUST be installed on a 'balanced pressure' (i.e. equal hot and cold pressures) system, I suggest the installation is acceptable from a technical point of view and if Mdljk wants better performance, this needs to be an 'extra'. On the other hand, if these 3 requirements have not been met, then the tap is not suited to the plumbing system at the house, the installation is illegal under the Water Supply (Water Fittings) Regulations 1999, and either the plumbing system needs to be modified or the tap needs to be replaced with one suitable for use with a traditional British mains cold, gravity hot system.
Excellent info Ric2013 - the tank is 4.4m above the tap outlet so 0.44 OP rather than 1.4? Interesting about the Blanco perhaps including check-valve technology. The tap is double lever, separate lever for hot and for cold (nothing thermostatic). You seem highly knowledgeable on the tech calcs side. Does the 4.4m head alter you conclusion above about being acceptable. Havent measured yet but first thing in the morning draw-off of hot water is certainly well in excess of 30 sec. Any further thoughts gratefully received.
 
Excellent info Ric2013 - the tank is 4.4m above the tap outlet so 0.44 OP rather than 1.4? Interesting about the Blanco perhaps including check-valve technology. The tap is double lever, separate lever for hot and for cold (nothing thermostatic). You seem highly knowledgeable on the tech calcs side. Does the 4.4m head alter you conclusion above about being acceptable. Havent measured yet but first thing in the morning draw-off of hot water is certainly well in excess of 30 sec. Any further thoughts gratefully received.
Yes. Sorry. 1.4 bar is a typo. I intended 0.44!

I'm not highly knowledgeable on the tech calcs - I'm just fairly good at maths and followed what John suggested, but thanks anyway.

I'm not saying the Blanco tap does incorporate check valves, but it's worth asking the question. The Water Regulations would generally require a tap that allows in-body mixing (as opposed to one that has separate internal waterways) to have check valves fitted if the pressures are not balanced (for various reasons that I have had explained to me by a Water Regulation officer of Dwr Cymru, but that seem a bit tenuous in your circumstances): still that's the law. However, if the manufacturer of a WRAS-approved tap (and I expect Blanco taps sold in the UK are all WRAS-approved) states that separate external check valves are not needed with unbalanced pressure installations, then the manufacturer is saying they have got around the need some other way (such as adding incorporated check valves, for example) and this workaround is legally accepted. External check valves are a nuisance as they WILL restrict flow.

If double lever, I can't understand why your mixed flow is LESS than with cold only. This is weird. So you have the cold fully open, and when you also open the hot, the flow of water issuing from the tap drops instantly (and visibly?). The effect is instant, I take it? If instant, I'd talk this through with Blanco and see if they can understand what their tap is doing as it sounds quite clever. If not instant (say a 30-second lag), then I can only assume that as your cistern starts to refill the use of cold water to do this is then competing and dropping the pressure at the tap (and if so, check your mains stopcock and external stopcock are both fully-open: sometimes people leave them half shut for some reason).

I'd suggest the 30-second rule applies unless there was a previous kitchen tap that broke the rule in which case I'd say a plumber has worked with due care if the new tap is no more non-compliant than the old one.

Out of interest, what is the exact name of the tap, as I'd like to see what we're discussing.
 
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Yes. Sorry. 1.4 bar is a typo. I intended 0.44!

I'm not highly knowledgeable on the tech calcs - I'm just fairly good at maths and followed what John suggested, but thanks anyway.

I'm not saying the Blanco tap does incorporate check valves, but it's worth asking the question. The Water Regulations would generally require a tap that allows in-body mixing (as opposed to one that has separate internal waterways) to have check valves fitted if the pressures are not balanced (for various reasons that I have had explained to me by a Water Regulation officer of Dwr Cymru, but that seem a bit tenuous in your circumstances): still that's the law. However, if the manufacturer of a WRAS-approved tap (and I expect Blanco taps sold in the UK are all WRAS-approved) states that separate external check valves are not needed with unbalanced pressure installations, then the manufacturer is saying they have got around the need some other way (such as adding incorporated check valves, for example) and this workaround is legally accepted. External check valves are a nuisance as they WILL restrict flow.

If double lever, I can't understand why your mixed flow is LESS than with cold only. This is weird. So you have the cold fully open, and when you also open the hot, the flow of water issuing from the tap drops instantly (and visibly?). The effect is instant, I take it? If instant, I'd talk this through with Blanco and see if they can understand what their tap is doing as it sounds quite clever. If not instant (say a 30-second lag), then I can only assume that as your cistern starts to refill the use of cold water to do this is then competing and dropping the pressure at the tap (and if so, check your mains stopcock and external stopcock are both fully-open: sometimes people leave them half shut for some reason).

I'd suggest the 30-second rule applies unless there was a previous kitchen tap that broke the rule in which case I'd say a plumber has worked with due care if the new tap is no more non-compliant than the old one.

Out of interest, what is the exact name of the tap, as I'd like to see what we're discussing.
Ric2013
They are Blanco Arti -specified as low-pressure. Here is the link
Will repeat the separate vs combined test again tomorrow as my data does seem strange.
I shall update you tomorrow

Thanks for all your help
Mdljk
 
I have a similar two lever mixer downstairs, the unit is a Franke but don't know if the mixer is, it was all installed 10 years ago as one unit, the hot gravity (0.45 bar) flow is 5.0 LPM and the mains (2.4 bar dynamic) cold is 11.1 LPM so very close to yours, I would be a little skeptical of their claimed 7.9 LPM at 0.3 bar
 
I have a similar two lever mixer downstairs, the unit is a Franke but don't know if the mixer is, it was all installed 10 years ago as one unit, the hot gravity (0.45 bar) flow is 5.0 LPM and the mains (2.4 bar dynamic) cold is 11.1 LPM so very close to yours, I would be a little skeptical of their claimed 7.9 LPM at 0.3 bar
Hi John G. It is very helpful to see that similar comparison. I am indebted to you for your doubtless having performed that test just for my needs. Thank you
 
I am getting 14.5 Lpm combined and the implication is that I should be happy with that. But surely that figure of 7.9 Lpm combined flow-rate must be when both hot AND cold are at 0.3 bar

Hi John g

so I tested hot alone - 4.0 Lpm (0.4 bar head) Cold 12 Lpm (mains pressure) and when both were on together it was 9.5 Lpm. Was that the method you expected?
Confused: combined flow rate is 14.5, or 9.5 l/m? If 14.5, you can ignore #22 paragraph 4!
 
Ok, I think your taps are designed to flow ~ 3.9/4LPM each @ 0.3M head.

You got 4LPM hottap & 12LPMcoldtap, now, based on my own tests, you will not get 16LPM combined with both taps fully opened but you should ( I did) get 12 LPM, you won't get 16 LPM, you certainly shouldn't be only getting 9.6LPM except that the cold water is flowing back towards the HW cylinder, I would suggest leaving both levers fully opened, isolate the hot supply somewhere upstream of the hottap lever (leave this fully opened) and measure the flowrate.

Re mixing, again from my own tests, if you separately match the cold and hot flows by throttling the cold (hot full open) then you will get close to double the hot water flow, I got 85 to 90% of the hotflowX2.
So depending on the water temps you should be able to use up to (almost) the full HW flow, ie if you had 60/10/40(mixed) you will get a max of 6.7LPM@40C, if the temps are 70/10/40, then you should get a Very max of 8.0 LPM@40C.
 
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Ok, I think your taps are designed to flow ~ 3.9/4LPM each @ 0.3M head.

You got 4LPM hottap & 12LPMcoldtap, now, based on my own tests, you will not get 16LPM combined with both taps fully opened but you should ( I did) get 12 LPM, you won't get 16 LPM, you certainly shouldn't be only getting 9.6LPM except that the cold water is flowing back towards the HW cylinder, I would suggest leaving both levers fully opened, isolate the hot supply somewhere upstream of the hottap lever (leave this fully opened) and measure the flowrate.

Re mixing, again from my own tests, if you separately match the cold and hot flows by throttling the cold (hot full open) then you will get close to double the hot water flow, I got 85 to 90% of the hotflowX2.
So depending on the water temps you should be able to use up to (almost) the full HW flow, ie if you had 60/10/40(mixed) you will get a max of 6.7LPM@40C, if the temps are 70/10/40, then you should get a Very max of 8.0 LPM@40C.
Hi John g

Your data and predictions are close, as I have re-performed the tests with a second person helping me to swap out measuring jugs. The figures I got are as follows.

Hot only (from a 4.4 m head and perhaps 8 to 9 m of 15mm pipework including bends etc) = 4.2 Lpm (Your expectation of 4.0 Lpm @ 0.3 bar is probably equivalent including pipe runs and fittings to 0.3 Bar?)

Cold only (mains pressure which is good, same pipe-run set-up) = 11.0 Lpm.

Hot and cold running consecutively = 10.Lpm ( your expectation = 12.0 Lpm

The Company’s Director has offered to swap-out the two standard 15mm ball service valves for 15mm full-bore valves. I have done this myself in the past for poor upstairs hot water to the bathroom sink but it had no-effect.

So John g - would you agree with me that (despite the fact that the monobloc taps in the Utility room less than 3.0m away have good flow-rates) the contractor is likely to say that they have no control over my existing water pipes, they have fitted low-pressure taps, they will minimised service -valve resistance, that is all we can do.

It’s a mystery.
 
Confused: combined flow rate is 14.5, or 9.5 l/m? If 14.5, you can ignore #22 paragraph 4!
Hi Ric2013

At your prompting have re-run the test with a second person to swap out measuring jugs

Hot only = 4.2 Lpm
Cold only = 11.0 Lpm
Both = 10.0 Lpm

So the ‘combined’ flow rate is less than the sum of the individual flow rates and even Less than the Cold-only rate
 
Hi John g

Your data and predictions are close, as I have re-performed the tests with a second person helping me to swap out measuring jugs. The figures I got are as follows.

Hot only (from a 4.4 m head and perhaps 8 to 9 m of 15mm pipework including bends etc) = 4.2 Lpm (Your expectation of 4.0 Lpm @ 0.3 bar is probably equivalent including pipe runs and fittings to 0.3 Bar?)

Cold only (mains pressure which is good, same pipe-run set-up) = 11.0 Lpm.

Hot and cold running consecutively = 10.Lpm ( your expectation = 12.0 Lpm

The Company’s Director has offered to swap-out the two standard 15mm ball service valves for 15mm full-bore valves. I have done this myself in the past for poor upstairs hot water to the bathroom sink but it had no-effect.

So John g - would you agree with me that (despite the fact that the monobloc taps in the Utility room less than 3.0m away have good flow-rates) the contractor is likely to say that they have no control over my existing water pipes, they have fitted low-pressure taps, they will minimised service -valve resistance, that is all we can do.

It’s a mystery.
Generally speaking, I would say yes, those flows are more or less what I expect and similar to mine but swapping the ball valve to full flow can only improve things but I would be surprised if the cold flowrate would double, did/can you measure the hot flowrate only from the Utility?

Its a mystery though as you say that you get 25LPM from the Utility cold main will require 5 times the deltaP, for example, 9M of 15mm pipe will have a pressure loss of 0.1bar @ 12LPM but 12M of 15mm pipe will have a pressure loss of 0.5 bar @ 25LPM.
 
Okay. So the mixed flow being less than the cold alone remains a mystery. But basically the mixer tap works and were the issue flow rates alone, I'd suggest the customer ought to be happy. 4.2 l/m hot is borderline for a kitchen tap, but if the customer wants a mixer, that may be about right.

An installation in breach of the Water Regulations (unless the plumbing firm is a Watersafe Approved contractor) leaves the customer liable to (unlikely) prosecution. I would recommend the OP contact the local Water Board ("Water Undertaker") and discuss the matter with the Water Regulations department. If check valves are not fitted, that is probably a breach of the Water Regs (nothing in the Blanco link supplied suggests check valves not required).

But fitting check valves here would probably ruin the flow rate on the hot side so the company that supplied and installed the tap should have initiated a discussion in which the company states the tap installation won't flow properly (once the check valves are fitted) so does the customer want to have a hot water pump fitted/pipework upgrades or would he or she not prefer a more suitable tap instead? I'd have that conversation - which is probably why I'll never be the cheapest.

I would not have wanted to fit that specific tap to a mixed-pressure system and would not expect the customer to know anything about plumbing hence I would not have recommended it. I'd have suggested a biflow tap (no check valves required) and, as for the time to get hot water, how was the old tap and what does the customer want to to ensure the new tap is no worse? At a guess, I'd suggest the firm may have good intentions but possibly lacks a qualified plumber - hence a lack of technical understanding.

For what it's worth, the hot washbasin tap in my own home is a 1/2" hot only tap. I also have a vented cylinder. The bathroom is on the first floor, the cistern on the loft floor above the first floor and the house has low ceilings. I probably have 1.5m head. I can't remember the exact flow, but, from memory, I'd suggest it's nearer 9 than 4.2 litres per minute (possibly it's as much as 12). I have hot water in under 15 seconds. Yes, the pipework was designed and installed to the nth degree, but what really helps is the tap mechanism is to BS1010 and specifically designed for 0.1 Bar use. The continental firms don't really get British systems as the UK refused to accept mains pressure hot water was safe until the foreigners had used it for 50 years, so our older-design mechanisms with washers really do work best with lower pressures.

Try giving PeglerYorkshire a ring and seeing what the flow rates are for their 0.1 Bar kitchen mixers?

The problem with changing the isolators is that there isn't a huge flow rate to begin with, so such a restriction as a 10mm bore valve won't be causing very much restriction: the restriction, it would seem, is the tap itself, but it may help - slightly.
 
What head is giving you this 7.5LPM?, 12M of 15mm pipe will have a pressure loss of 0.55M @ this flowrate which is > your gravity head available?.
Hi John G

the head for both kitchen (4.2 L/m) and Utility Room (7.5 L/m) is from a vertical height from tge bottom of each monobloc outlet of 4.4m. So the direct 'vertical' head would be 0.44 bar but I assume that is impaired by long pipe runs (8m+) and bends. Interestingly, I have looked at the pipework and the plumber has arranged it so that there is a 90 degree bend directly onto the hot water tail! Something that even I as a diy-er know you should avoid especially in graviity fed systems.
 
What head is giving you this 7.5LPM?, 12M of 15mm pipe will have a pressure loss of 0.55M @ this flowrate which is > your gravity head available?.
I make it head loss of 0.05m per m run. (Yorkshire tube technical guide section 4-2).
 

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