Kitchen tap choice for mains cold and gravity fed hot

[JoeA]

Hello,

I need to choose a new tap for our soon to be fitted kitchen, and I have realised having a gravity fed system will limit my choice somewhat.

Cold water tank is in the loft approx 5m above ground level, but tap outlet is about 1m off the ground, so am I right in thinking this will give me a hot water pressure of about 0.4 bar? I've no idea what my cold mains pressure is, but I am presuming somewhat more than that!

From what I've read, the advice seems to be that if you have unbalanced pressures (and don't want to go down the route of fitting pressure reducing valves, non return valves etc as these reduce flow rate) then the best option is to fit a dual flow tap where the water only mixes at the spout?

I've read a few threads online where people with unbalances pressures who chose single flow taps are having all sorts of problems with backflow and no hot water etc etc.

However, casting an eye over our current tap (picture attached), it seems to me that it is not dual flow, becuase when I turn on the hot water, the spout gets very hot? Does this mean it is definately single flow?

We have never had any issues with this tap, we've always been able to get a nice temperature for washing up, cold water flow is fine. Looking underneith the sink, do those white isolating valves also incorperate a non return valve? Is that why I'm not having any problems?

My next question is, with my system, considering I appear to have a working single flow two lever tap - would I see any appreciable difference between that and a single flow single lever tap? Presumable they both mix the water in the tap body, and the only difference is using two quarter turn cartridges vs a single lever cartridge? Cos I quite fancy the look of the single lever taps.

Presumably I still need to go for a tap designed for low pressure systems, but it seems like my non return valves are solving the fact my pressures are also unbalanced?

Or should I play safe and by a dual flow tap? (I can see there is much less choice if I go down this route).

Many thanks for any advice!

 

[bernardgreen]

Or should I play safe and by a dual flow tap? (I can see there is much less choice if I go down this route).

Dual flow ( separate channels through the spout ) means the cold water you draw for drinking will not be contaminated by anything in the hot water system.

 

[Madrab]

You don't have NRV's fitted, the white plastic valves are just JG push fit isolation valves. The 2 flexi pipes you have fitted will be restricting the flow.

Your cold mains pressure may not be much higher than your gravity hot water ergo you're not seeing much impact in a single flow tap but some see issue from mix in the body taps and some don't, it's usually where the cold mains pressure is much higher.

Single level monobloc taps have a cartridge with typically narrow water ways and tend to be classed as HP (high pressure). Fitting NRV's on the hot side can sometimes sort it but they can also restrict the flow. Some taps are now shipping with a tap tail that has an NRV already incorporated .... the right hand flexi in this pic.

I appreciate that this doesn't answer the question directly but it's hard to be specific as every system can be different. Sometimes it's just a try and see.

 

[JoeA]

Thank you both for your replies.

In terms of hot water contaminating the cold supply, I don't know... We've been OK so far with our current tap... No health issues as far as I can see? How important is this issue? My worry with dual flow taps is the water coming out unmixed so you get boiling hot and cold water rather than nicely mixed warm?

I totally get the point about single lever taps having the cartridge which restricts the flow, which may cause us a problem.

I think the safest course of action is to just get a tap as similar as possible to our current one as we know that works. So something that is designed for 0.4 bar or lower, and has two separate levers...

 

[oldbuffer]

1. Your existing one is a dual flow tap.
2. Normally the cold flows around the outside of the inner tube, and the inner tube carries the hot.
3. However, if it is connected the wrong way round, the spout will get hot even if you are running mixed hot and cold.
4. The outer may also get hot by heat radiation, particularly with a metal spout end.

 

[JoeA]

1. Your existing one is a dual flow tap.
2. Normally the cold flows around the outside of the inner tube, and the inner tube carries the hot.
3. However, if it is connected the wrong way round, the spout will get hot even if you are running mixed hot and cold.
4. The outer may also get hot by heat radiation, particularly with a metal spout end.

You're definitely sure it's a dual flow tap? Is there any other way to check? I've tried looking up the spout but I can't see anything.

 

[Madrab]

If you unscrew the aerator off the end of the spout, you should be able to see 2 distinct pipes, the outer and an inner pipe. I must be honest I though, I would have lent more towards it being a mix in the body type, single flow, but it should be easy to check.

Is it 1/4 turn valves?

 

[JoeA]

If you unscrew the aerator off the end of the spout, you should be able to see 2 distinct pipes, the outer and an inner pipe. I must be honest I though, I would have lent more towards it being a mix in the body type, single flow, but it should be easy to check.

Is it 1/4 turn valves?

Thanks, that's exactly what I tried to do and I couldn't see any evidence of two distinct pipes, I could only see one dark hole... Yes they are quarter turn valves.

 

[JoeA]

I think this proves its not dual flow, I shone a torch up and could only see one large hole for at least 4-5cm up the spout.

Plus, running hot water only makes the spout very hot, but it cools immediately as soon as you turn on the cold.

 

[JoeA]

What does a dual flow tap feel like to use? Since the cold water is on the outside does it feel weird when washing up? Do you freeze your fingers one second then scald then the next? It doesn't sound like the water can be very well mixed as it comes out.

 

[Madrab]

No Not at all, that why I mentioned to take the aerator off. usually the flows mix at the top of the spout before it hits the aerator, then it's fully mixed. The older ones used to have a dual spout where you could feel the different flows but most of them now have the aerators.

 

[JoeA]

Ahh, right of course - so the double outlet appears behind the aerator and then coming through the aerator would mix the flow.

I've just tested turning our hot and cold valves on full, and the cold water completely overpowered the hot, so only cold comes out. In order to get a comfortable temperature you have to "ride the valve" on the cold side to reduce the flow to point where the hot water can flow too.

I think a dual flow low pressure tap sounds like the best option. I think this one might be just what I'm after :

https://www.sinks-taps.com/shop/semplice-twin-lever-monobloc-kitchen-tap.html?sku=BLU2089

Many thanks for all your help!