mixer taps supply pressures

[elmsoft]

Fitting new taps to a bathroom basin, it occurred to me that the hot supply pressure is from a static head of about 3 metres or so, while the cold is mains pressure which is clearly way more than that.
Is there not a danger that the cold pressure could, in some circumstances, force the hot supply in the wrong direction?
Should there not really be some sort of non return valve on the hot feed?

 

[hazetimesfive]

No, because then you will get no hot water as the cold will keep the nrv closed probably

The answer is not mixing unbalanced supplies

 

[elmsoft]

So how I balance the supplies?

The cold mains is always going to be greater than the hot header. Wouldn't fill it otherwise. So this must be the common situation for all mixer taps?

 

[HERTS P&D]

In my basin I have cold mains pressure and hot water from the tank, I done it like this so that when we brush our teeth it's from the mains and not stored water, also it's easy to get a glass of water during the night rather than go downstairs.

I made sure the water in the tap mixers at the end of the spout and not in the body of the mixer tap, so yes it can be done. I didn't fit nrv.

Andy

 

[bolshy]

By rights all mixers (other than combination type) are supposed to be fitted with check valves on hot and cold feeds to comply with water regulations, although from my experience less than 1% are. A combination tap doesn't need check valves (the hot and cold water are kept in separate channels right up to the outlet nozzle).
I would say fitting a single check valve to the hot and cold supply in this case is good practice, unless its a combination. Is the new mixer tap on flexibles? Gravity hot water tends to give poor flow on monobloc mixers.

 

[Charnwood]

Most mixers nowadays are 'dual-flow' meaning the hot and cold water don't meet until they are at the end of the spout. Some even have the hot water on the centre of the spout so the surface of the spout never becomes too hot. Ideal Standard call theirs 'Cool Body'.

 

[elmsoft]

The taps are monobloc with flexibles and yes the hot flow is pretty weak anyway.
I contacted the suppliers help line and they "recommend" no greater differential than 0.5 bar.
If 3m head = about 0.3 bar then I can't even source a reduction valve that would achieve that. ( 1.5 bar min output seems standard)
But I really don't want feed from header tank as HERTZDRAINAGE2010 pointed out.
Common sense tells me that there must be thousands of these mixer taps sold and very few PRVs !

 

[HERTS P&D]

The tap I fitted to my basin was for low or high pressure and it works fine with no problems.

Andy

 

[Charnwood]

PRVs are generally available that will reduce to 1 bar, but a couple of manufacturers do ones that will go down to half a bar.

 

[bolshy]

Your tap will work but don't expect decent hw flow from it through a flexible. And if you fit the check valves you've done a proper job iaw regulations and protected your mains and DHW, in case of tap component failure or loss of water mains pressure. It's your call whether you fit them. I wouldn't go to the expense of fitting a reducing valve.