Low pressure mixer spray tap recommendations ?

[Splitty]

I'll be installing a new kitchen, DIY, and the Mrs wants a mixer tap with a switchable spray/regular flow. No pullout with hose but more like one with a spiral round the outer hose that lifts out of a mount and you can move it about a bit. Something like you see on catering sinks. Now stay with me on this as I'm not a plumber !
I have gravity fed hot water, but mains fed cold, and the cold pressure is very high.
Currently the mixer tap we have inherited when we moved, allows the cold water to push back the hot water to the extent that if you try to mix them to get warm, it's a bit of a balancing act to get it right .
If you get it wrong and turn the cold off, there's quite a few feet of cold water to run out of the hot tap to get hot water back out again !
So clearly, this tap is not up for the job and its gonna be changed anyway.

Any recommendations for a decent model mixer that fulfils the wife's wishes that can allow easy mixing without the backflow problems would be greatly appreciated. Big ask, I know but I'm sure some of you guys have come across this problem before. Your average retailer online or in store doesn't seem to provide the info l need so l really need your help. Many, many thanks in advance. Cheers.

 

[Alan Wright]

The reason cold water pushes back through the hot pipe is that either your tap lacks a non return valve or if it has a non return valve it is stuck in the open position. Thats an easy fix if you fit a non return on the hot however you also want to change your tap. Fit a 22mm single check valve and use 22mm to 15mm 3 piece reducers.

The new tap you describe needs mains pressure on the hot and cold.
Most traditional taps will give you a decent flow if you have gravity hot and gravity cold but most if not all of the new taps need mains pressure hot and cold.

You can achieve the equivalent of mains pressure hot if you double boost the gravity hot with a ShowerPowerBooster SP21S on the hot pipe.

 

[Splitty]

The reason cold water pushes back through the hot pipe is that either your tap lacks a non return valve or if it has a non return valve it is stuck in the open position. Thats an easy fix if you fit a non return on the hot however you also want to change your tap. Fit a 22mm single check valve and use 22mm to 15mm 3 piece reducers.

The new tap you describe needs mains pressure on the hot and cold.
Most traditional taps will give you a decent flow if you have gravity hot and gravity cold but most if not all of the new taps need mains pressure hot and cold.

You can achieve the equivalent of mains pressure hot if you double boost the gravity hot with a ShowerPowerBooster SP21S on the hot pipe.

Thank you very much. This is the kind of info I need. Very much appreciated and now I have something to work with. I have a spare non return valve in my plumbing spares too. Cheers.

 

[John.g]

Thank you very much. This is the kind of info I need. Very much appreciated and now I have something to work with. I have a spare non return valve in my plumbing spares too. Cheers.

I would suggest installing a swing check NR valve, preferably on the horizontal and leaning back a little towards the flow direction as the spring loaded type will restrict the hot flowrate with that very low head of around 5M.

 

[Splitty]

I would suggest installing a swing check NR valve, preferably on the horizontal and leaning back a little towards the flow direction as the spring loaded type will restrict the hot flowrate with that very low head of around 5M.

Thank you for your reply. I was concerned about my non return valve not allowing the low pressure through as mine is spring loaded as my pressure is very low on the hot water. A swing check NR valve is what it will have to be then.
I was hoping there would be a mixer tap out there that was divided all the way to the outlet so there was no interference between hot and cold. Seems not at the moment. Cheers for the valve info.

 

[John.g]

Thank you for your reply. I was concerned about my non return valve not allowing the low pressure through as mine is spring loaded as my pressure is very low on the hot water. A swing check NR valve is what it will have to be then.
I was hoping there would be a mixer tap out there that was divided all the way to the outlet so there was no interference between hot and cold. Seems not at the moment. Cheers for the valve info.

I have one, its a (15 year old) Franke Moselle, a dual flow spout, with a swivel on the end, and two taps, the mixing takes place in the deaerator as it exits the spout, there should be a equivalent around but ensure that the mixing does take place in the spout. I also have another downstairs mixer where the mixing is before the spout but I do have a swing check NRV on the hot, the cold mains pressures are 3.8bar static and ~ 2.5bar dynamic with either tap full on, the CWSC which supplies the HW cylinder gives a head of 5.5M, 0.55 bar.

 

[Alan Wright]

When I suggested a non return valve I specified a 22mm single check valve from personal experience because the spring is not too fierce and because the pressure acts on a big dome. In the direction of flow the pressure opens the dome and there is plenty of space for water to get by so there is very little head loss. If used on 15mm pipe use 22mm to 15mm three part reducers.
Do not use 15mm non return valves on 15mm pipe, use a 22mm single check valve and taper down.
If you had mains pressure it would not matter.

 

[Splitty]

When I suggested a non return valve I specified a 22mm single check valve from personal experience because the spring is not too fierce and because the pressure acts on a big dome. In the direction of flow the pressure opens the dome and there is plenty of space for water to get by so there is very little head loss. If used on 15mm pipe use 22mm to 15mm three part reducers.
Do not use 15mm non return valves on 15mm pipe, use a 22mm single check valve and taper down.
If you had mains pressure it would not matter.

Understood, 22mm on a 15mm reducer. Got it, thanks for reiterating the point and the excellent explanation. To be honest, I'd read your first comment on this set up but it didn't register and lodge in to my brain ( if you know what I mean ). Its an afe thing, I've had far too many orbits round our sun these days and the old grey matter is struggling a bit.
Thanks again for the info, very much appreciated. Cheers.......Ü

 

[Splitty]

I have one, its a (15 year old) Franke Moselle, a dual flow spout, with a swivel on the end, and two taps, the mixing takes place in the deaerator as it exits the spout, there should be a equivalent around but ensure that the mixing does take place in the spout. I also have another downstairs mixer where the mixing is before the spout but I do have a swing check NRV on the hot, the cold mains pressures are 3.8bar static and ~ 2.5bar dynamic with either tap full on, the CWSC which supplies the HW cylinder gives a head of 5.5M, 0.55 bar.

I don't have the means to test my hot water pressure but as a rough guide, I recently moved into a 1982 built, two storey house with a typical big ol' copper hot water cylinder upstairs in the airing cupboard and a small header tank in the loft. My ceiling height downstairs is about 9'6". Allowing for 6" joists and floorboards, we're roughly about 10 feet to the base of the cylinder with approximately 18-20 feet of 15mm pipe to the tap. Would it be possible to estimate the head pressure expectation at the tap. Obviously this isn't a new installation and I'll appreciate there will be some degree of furring up in the pipework.
Also, you mention a dual flow spout, maybe this is where I need to do a bit more research too and include the 22mm NRV in the circuit along with this type of tap. I need to see if I can source a monobloc version as the sink can only have one tap hole, you know, the Mrs wants what the Mrs wants !
Many thanks again.

 

[Basher]

10 metres head provides 1 bar pressure. So 1 metre head = 0.1 bar etc
If the tank in your loft is a cold water storage tank feeding the hot water cylinder, then estimating the distance between the surface of the water in the loft tank down to the tap will give you the head.
Say the vertical distance from the cwst in your loft to the tap is 20ft = about 6 metres, that gives 0.6 bar at the tap.
The length of pipe affects the flow rate, not the pressure, but useful to know.

You say 'small header tank' in the loft, which makes me think of expansion tank for the central heating. Do you have a decent size cold water tank? Or is your hot water cylinder a Fortic or combined tank? If the latter the 0.6 bar above won't be correct!!

 

[John.g]

I don't have the means to test my hot water pressure but as a rough guide, I recently moved into a 1982 built, two storey house with a typical big ol' copper hot water cylinder upstairs in the airing cupboard and a small header tank in the loft. My ceiling height downstairs is about 9'6". Allowing for 6" joists and floorboards, we're roughly about 10 feet to the base of the cylinder with approximately 18-20 feet of 15mm pipe to the tap. Would it be possible to estimate the head pressure expectation at the tap. Obviously this isn't a new installation and I'll appreciate there will be some degree of furring up in the pipework.
Also, you mention a dual flow spout, maybe this is where I need to do a bit more research too and include the 22mm NRV in the circuit along with this type of tap. I need to see if I can source a monobloc version as the sink can only have one tap hole, you know, the Mrs wants what the Mrs wants !
Many thanks again.

Can you just get a container and hold it under the hot tap for exactly 15 secs, measure this with a 1 litre container, X 4, this will give you the flow rate in LPM,

A dual flow spout does not require a NRV.

My Franke requires just one hole but has two taps. the hot tap flows 4.5LPM (the cold, 9.7LPM). The upstairs hot (with the 1/2ins NRV) flows ~ 3.5LPM and I think I lost around 10% flowrate when I installed the NRV so ~ 4.0LPM without the NRV and 3.5LPM with it installed.

 

[Splitty]

Excellent explanation, thank you for this. I think this is what I'm really looking for, a dual flow spout and no NRV to fit, although fitting one won't be a problem.Many thanks, much appreciated, Cheers.

 

[MikeJhn]

Most mixer spray taps are designed for mains pressure hot feed, you may find a pressure/flow booster is required for the tap of choice, look for one with slip joints to enable easy fitting without taking your hot water system apart.

 

[Splitty]

Most mixer spray taps are designed for mains pressure hot feed, you may find a pressure/flow booster is required for the tap of choice, look for one with slip joints to enable easy fitting without taking your hot water system apart.

Thankyou, I have already installed a hot and cold isolating valve under the sink to enable easier tap swap over. Just looking for a dual flow mixer now, as previously mentioned by John.g.
I know there are mixers out there that will accommodate low pressures and I was finding it very difficult to source one as there is little or no info for technical specs from suppliers. So my original outset was asking if anyone knew of such a mixer so I didn't have to do the hard research. Me trying the lazy route now. 😊