Kitchen mixer tap, need a new one.

grumbler

GDB2222 said:

grumbler said:

GDB2222 said:

Norman_bn23 said:

HI, sorry been away.

Yes indeed the hot water is verylow tank pressure,  when mixing hot & cold the cold mains would push up the hotwater feed pipe and cause the loft tank to overflow 

The dualflow tap mentioned above is on order.

You can easily stop the tank overflowing with a check valve, but of course that would mean you were washing up under cold water. So, your solution seems a good one. 

It's not about the tank overflowing, but mainly the safety regulations preventing any water from the loft tank getting into the mains network in a fantastic scenario when the pressure in it becomes too low or even negative.

How does the shower work?

In the bathroom both hot water and cold one have the same pressure as both are fed from the tank in the loft. As simple as that. Drinkable mains cold water is in the kitchen only (and, possibly, in the electric shower).

I am surprised that a dual flow tap is essential, btw.

It seems that now a normal (not dual flow) mixer tap is allowed if installed with non-return valve(s).

nofoollikeold

Most non-return valves have a spring which closes the valve if the flow is in the "wrong" direction.  This spring acts against the pressure from the source of flow, and thus reduces the pressure.  Given that the pressure from a vented hot water cylinder at the kitchen tap is likely to be around 0.3 bar (two storey property, cold water cistern in loft) this may leave insufficient pressure to get a decent flow from the tap.
You can get non-return valves without a spring, but these require an internal flap to be vertically oriented.  Not always possible.

grumbler

In this case it's required mainly in the high-pressure cold water pipe. IMO, the loft  tank overflowing is impossible even in a bungalow (unless you attach a hose to the tap - very long or  with a tap at the end).

GDB2222

I don’t doubt the OP.