Can water flow rate be measured at the supply pipework?

[Mdljk]

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.

 

[Ric2013]

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!

 

[John.g]

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.

 

[Mdljk]

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.

 

[Mdljk]

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

 

[John.g]

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.

 

[Mdljk]

Hi John g

The hot water only Utility Room monobloc, 3m further along the supply pipe run, is 7.5 Lpm

 

[John.g]

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?.

 

[Ric2013]

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.

 

[Mdljk]

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.

 

[Ric2013]

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).

 

[Ric2013]

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 [elipses] Something that even I as a diy-er know you should avoid especially in graviity fed systems.

Not ideal, but not necessarily a problem either. Better to use pulled bends, but the rule against elbows is often over-stated.

 

[John.g]

So a 12 m run is 0.6M head loss? Oh yes the
Head is 4.4 M so ok so

 

[Mdljk]

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.

Thanks Ric2013

The plumbing sub-contractor is a registered gas and unvented cylinder qualified heat engineer and plumber. At the same time he's a had several call backs. I agree that full-bore isolatirs is unlikely to help especially as....,he's gone from plastic to copper on the last metre or so and had to adjust his second fix so that he has a JG elbow giving him a 90 degree short pioe-run to take him to the tap-tail. Even I as a diyer knowcthat is to be avoided especially in gravity systems.

Would re-adjusting the last metre or so (reverse fitting) so that you eliminate that (unnecessary) final bend alieviate the issue?

 

[Mdljk]

Thanks Ric2013

The plumbing sub-contractor is a registered gas and unvented cylinder qualified heat engineer and plumber. At the same time he's a had several call backs. I agree that full-bore isolatirs is unlikely to help especially as.***,he's gone from plastic to copper on the last metre or so and had to adjust his second fix so that he has a JG elbow giving him a 90 degree short pioe-run to take him to the tap-tail. Even I as a diyer knowcthat is to be avoided especially in gravity systems.

Would re-adjusting the last metre or so (reverse fitting) so that you eliminate that (unnecessary) final bend alieviate the issue?

Sorry Ric2013

I can see now that you've already covered that and you don't think its an issue.

Thanks

 

[John.g]

What make is the Utility mixer?

 

[Ric2013]

The plumbing sub-contractor is a registered gas and unvented cylinder qualified heat engineer and plumber.

May not mean he's Watersafe Approved as I'm fairly sure it's a separate scheme. It's arguably a cartel. I'm not qualified enough to join, but I'm not sure I would anyway and it would not surprise me if lots of good plumbers are not members as I doubt it gets you much in the way of extra work.

The point is that responsibility for compliance with the Water Regulations falls to the homeowner unless the plumber is a member of that scheme in which case the plumber takes responsibility. But this does not mean the unregistered plumber should be doing uncompliant work. Actually all the more reason for the plumber to make the work as compliant as possible!

 

[Mdljk]

What make is the Utility mixer?

It is 25 years old John g so I confess I dont know. However I do know that currently there are only a limited number of 0.2 bar min pressure in monobloc and nit that pretty while I can find 0.1 bar kitchen taps but they have separate capstan heads on one chassis but are not monobloc. So I assume that since the Utility is cartridge type it is probably 0.3 bar as well.

May not mean he's Watersafe Approved as I'm fairly sure it's a separate scheme. It's arguably a cartel. I'm not qualified enough to join, but I'm not sure I would anyway and it would not surprise me if lots of good plumbers are not members as I doubt it gets you much in the way of extra work.

The point is that responsibility for compliance with the Water Regulations falls to the homeowner unless the plumber is a member of that scheme in which case the plumber takes responsibility. But this does not mean the unregistered plumber should be doing uncompliant work. Actually all the more reason for the plumber to make the work as compliant as possible!

I can confirm that no anti-back flow valves

 

[Mdljk]

It is 25 years old John g so I confess I dont know. However I do know that currently there are only a limited number of 0.2 bar min pressure in monobloc and nit that pretty while I can find 0.1 bar kitchen taps but they have separate capstan heads on one chassis but are not monobloc. So I assume that since the Utility is cartridge type it is probably 0.3 bar as well.

I can confirm that no anti-back flow valves

....have been fitted and it is unlikely that there are any inside the Blanco tap. I think all of this is a result of most homes having pressurised mains hot water from combi boilers unlike my system boiler/gravity hw

 

[John.g]

The cartridge type look very restrictive, only a temporary test but removing the diffuser/aerator might improve matters.

 

[Mdljk]

The cartridge type look very restrictive, only a temporary test but removing the diffuser/aerator might improve matters.

Yes John G

Have remove aerator and am now getting 4.5 L/p (previously 4.2 Lpm ) that is a 7-8% improvement. Utility room at 7.5 L/m (and that is aerated!) is 7.5 L/m 78-79% better than kitchen

 

[Mdljk]

Yes John G

Have remove aerator and am now getting 4.5 L/p (previously 4.2 Lpm ) that is a 7-8% improvement. Utility room at 7.5 L/m (and that is aerated!) is 7.5 L/m 78-79% better than kitchen

Of more interest to me now is the unnecessary 90 degree JG end just before the tail. begin to wonder if most plumbers default to combi-boiler with sub- mains pressure hot water and forget sometimes that some of us have system boilers with gravity hot water that requires TLC with installations.

 

[Mdljk]

Of more interest to me now is the unnecessary 90 degree JG end just before the tail. begin to wonder if most plumbers default to combi-boiler with sub- mains pressure hot water and forget sometimes that some of us have system boilers with gravity hot water that requires TLC with installations.

#end = bend

 

[Ric2013]

Not convinced it'll be your problem, assuming all your pipework is 15mm, but always like to know when I'm wrong, so please do let us know how you get on and what the outcome is.

 

[John.g]

My tap is a "Perlator sink tap (p-ix 501 ib" and I get a very substantial increase in hot flow rate from 5.1 LPM to 6.6 LPM (29%) when I remove the very fine aerator/filter, the hot flows through the centre of the spout and the cold around this central core, don't know if you can get a more free flowing "spout" or not but maybe worth looking into because 6.6 LPM at 70C will give ~ 13 LPM at 40C from cold at 10C which should be sufficient for most purposes. The highest flow I see in the attached Franke file is 6 LPM (hot), from a "Moselle".
I think I actually have this moselle tap with the perlator swivel aerator.

Franke Moselle Bi-Flow Spout Chrome Tap

Franke Moselle Bi-Flow Spout Chrome Tap

www.plumbingproducts.ie