Poor HW pressure

[Bogart]

Another bit on the saga of the new kitchen sink/tap /waste arrangement. Waste now sorted only problem now is the proverbial poor pressure using a monobloc mixer tap. The cold provides 9L/min whilst the hot is 2.75L/min yes 2.75. In the attached piccy you can see the setup. The tap came with both the solid and flexible 10mm
pipe/hose. There is not room to get just the flexible straight into the base of the tap hence the metal portion. The hot is supplied via a F/E tank which with 'normal' taps
gives a decent flow as is 15mm all the way to the tap. You can see that this tap has JG emergency shut off valves on hot and cold which are themselves restrictive. Further back along the line are another pair of the same valve. Now to my mind all these restrictions are the cause of the poor hot flow. Up near the hot water cylinder
is Stuart Turner monsoon twin shower pump. Could this be incorporated into the system to overcome the poor pressure. Or should I really be concentrating on getting these poor restrictions out of the way ie full bore valves, there is not anything I can do, as far as I see, with the actual tap connections themselves.

 

[Aquarius]

Are you able to disconnect any of the pipework under the sink, and measure the flow rate there? This should help you figure out if it’s the tap or pipewpork arrangement.

 

[Bogart]

Are you able to disconnect any of the pipework under the sink, and measure the flow rate there? This should help you figure out if it’s the tap or pipewpork arrangement.

I could give that a go be interesting to see if any different, am assuming it will be
In the kitchen is currently a pair of taps at another sink where flow is fine. Utility room next to kitchen flow rubbish as yet, you guessed it another monobloc tap.

 

[Ben-gee]

You probably have a high pressure tap, and it won’t work well on your system .

There are monobloc sink mixers designed for low pressure, you need those. E.g. Franke rotaflow- in general look for a compression valve setup rather than a cartridge type. Also better to have a dual flow spout, then the cold won’t overpower the hot or back flow to cylinder

 

[Bogart]

You probably have a high pressure tap, and it won’t work well on your system .

There are monobloc sink mixers designed for low pressure, you need those. E.g. Franke rotaflow- in general look for a compression valve setup rather than a cartridge type. Also better to have a dual flow spout, then the cold won’t overpower the hot or back flow to cylinder

Tap states minimum pressure 0.5bar so I should be okay if I get shut of all these restrictions, hopefully.
Failing that what do you think to the merits of pumping possibly using the current shower pump or getting a new one?

 

[Ben-gee]

Yeah that’s not a low pressure tap, you want 0.1-0.2 bar. Anyway some manufacturers seem to think if water actually comes out that’s good enough.
If you fit the one I suggested you won’t believe the difference.

 

[Ben-gee]

I wouldn’t use your shower pump, unless it’s a whole house pump?
The cheapo pumps don’t like only one end being used.
I wouldn’t fit a pump just for this tap either, but it would definitely work to fit a single impeller pump on the hot side only should you so wish.

 

[Bogart]

Yeah that’s not a low pressure tap, you want 0.1-0.2 bar. Anyway some manufacturers seem to think if water actually comes out that’s good enough.
If you fit the one I suggested you won’t believe the difference.

Might if I, or more precisely she, had not spent £400 on this one. I nearly died when she told me.

 

[Ben-gee]

Ah, I see you’re up against a more formidable opponent than the laws of physics and fluid dynamics!

 

[Bogart]

Yes one could say that, I just go along with that it makes life so much easier.

 

[Bogart]

Bit of an update. I have removed the isolation vales upstream totally and replaced the restrictive ones at
the taps with full bore Pegler ball valves. Flow rates at the tap no change at all.
Have done as Aquarius suggested measured the pressure and flow directly off the 15mm pipework just after the ball vales before the monobloc restrictive pipework has its say. I connected up a pressure gauge and static pressures were cold 3bar, hot 0.5 bar maybe just. What I then found somewhat odd was that the cold flow rate stayed at 12L/min whereas the hot jumped up to match it ie 12L/min. I cannot understand why the cold flowrate is not streets ahead of the hot in this scenario.

 

[Bogart]

I wouldn’t use your shower pump, unless it’s a whole house pump?
The cheapo pumps don’t like only one end being used.
I wouldn’t fit a pump just for this tap either, but it would definitely work to fit a single impeller pump on the hot side only should you so wish.

I would like better hot at this tap and the utility one which is also. Can I fit just a pump on the whole house hot system. It exits the HW cylinder in 28mm pipe before appearing in bathrooms at 22mm and various taps at 15mm. All the old taps hot flow rates are ok just these 2 damned monoblocs. I suppose 15mm going down to what looks like 6mm through the tap pipework is a real bottleneck.

 

[exedon2]

Whole house pump on hot would transform your problem taps .
Check how much water storage you have as a first move these pumps can rapidly empty a cold feed tank!

 

[Ben-gee]

The reason the other hot taps work fine is because they are designed for low pressure, but I understand you have to keep this kitchen tap!

If you have lots of places you want it, then yes fit a single impeller Stuart Turner Monsoon to feed all your hot pipework.
Measure your cold mains pressure and buy a pump to match that ie 2 bar, 3bar etc etc.
Plumb it in properly and it will last you 20 years.

 

[Bogart]

Whole house pump on hot would transform your problem taps .
Check how much water storage you have as a first move these pumps can rapidly empty a cold feed tank!

Been up and measured it my rough calculations, comparing to new ones online, I reckon it has a capacity of around 35 galls. As there is only myself and the gaffer in here most of the time that should be more than enough. I will though alter the feed pipe though to 22mm as currently just before it enters the tank it goes to 15mm. No idea who thought that up.

 

[Bogart]

The reason the other hot taps work fine is because they are designed for low pressure, but I understand you have to keep this kitchen tap!

If you have lots of places you want it, then yes fit a single impeller Stuart Turner Monsoon to feed all your hot pipework.
Measure your cold mains pressure and buy a pump to match that ie 2 bar, 3bar etc etc.
Plumb it in properly and it will last you 20 years.

Will do.

 

[Bogart]

Many thanks guys for all your inputs is greatly appreciated.

 

[Ric2013]

What I then found somewhat odd was that the cold flow rate stayed at 12L/min whereas the hot jumped up to match it ie 12L/min. I cannot understand why the cold flowrate is not streets ahead of the hot in this scenario.

I'm only slightly surprised: you may have a very long run of cold pipe (including your supply pipe) back to the point where the effect of flow on working pressure (pressure with the tap/pipe running) becomes insignificant, whereas your hot pipe is a shorter run entirely in the house. Perhaps once cold is flowing, the working pressure becomes the same as the working pressure of the hot and so the flows are equal until you add the extra restriction of the tap itself.

FWIW I've fitted traditional washered low pressure taps to a bath with similar pressures to yours: and with the hot run in 22mm throughout with as few elbows and bends as possible, and flow exceeded 20l/m. Yet the cold, which was mains pressure, gave less than this.

 

[Bogart]

My situation is that both baths are fed hot and cold 22mm but again the hot is very poor but hopefully if, well when, I install a pump it should remedy that.

 

[Mdljk]

I could give that a go be interesting to see if any different, am assuming it will be
In the kitchen is currently a pair of taps at another sink where flow is fine. Utility room next to kitchen flow rubbish as yet, you guessed it another monobloc tap.

Hi Bogart

I have a similar issue to yours. Have you solved the poor flow-rate at hot outlet issue? Mine is 4.5 litres per minute but that is really poor so I can’t but imagine what your issue looked like.

Let me know if/ how you have overcome the problem .... 0.1 bar taps?

 

[Bogart]

Hi Bogart

I have a similar issue to yours. Have you solved the poor flow-rate at hot outlet issue? Mine is 4.5 litres per minute but that is really poor so I can’t but imagine what your issue looked like.

Let me know if/ how you have overcome the problem ***. 0.1 bar taps?

Am going to install a pump on the hot water side. Been meaning to do it for weeks now but as usual other things get in the way. Maybe I should sort it now so can tick another box off.

 

[Mdljk]

Whole house pump on hot would transform your problem taps .
Check how much water storage you have as a first move these pumps can rapidly empty a cold feed tank!

👍

 

[Mdljk]

Am going to install a pump on the hot water side. Been meaning to do it for weeks now but as usual other things get in the way. Maybe I should sort it now so can tick another box off.

Hi Bogart

Company have now agreed to fit full-bore service valves in place of the standard 15mm valves currently in place. If that is brings no significant improvement I may follow you down the pumped hot water route.

Thanks for the reply

 

[Bogart]

Hi Bogart

Company have now agreed to fit full-bore service valves in place of the standard 15mm valves currently in place. If that is brings no significant improvement I may follow you down the pumped hot water route.

Thanks for the reply

I would doubt full bore service valves will make much, if any, difference, but every little helps.

 

[Mdljk]

I would doubt full bore service valves will make much, if any, difference, but every little helps.

My thoughts exactly Bogart. The service valves ARE throttled down to 10mm ball/bore but they connect to 10mm copper then tails - yes - full-bore eliminates only about 2 inches of 10mm pipe. Still, as you say, every bit helps and you never know. I may have a go at removing the aerator. I've heard they can harbour factory debris.

Cheers