Mixer tap on a gravity fed hot water system

[ksareen]

Hi all

Just moved into a house and out of several things the wife complained about was that there were seperate taps for HOT and COLD in the bathroom sink. She wanted a MIXER instead and she gets what she wants.

The basin HOT water tap is gravity fed but the mixer shower valve is pump fed (negative head). The expansion tank (at the top), header tank (in the middle) and copper tank (at the bottom) are all in the first floor airing cupboard.

The issue I've now is that the HOT WATER pressure is much less compared to stand alone tap. The COLD WATER is as good as before but when used as a MIXER tap, the cold is actually pushing HOT WATER back and filling up the HEADER TANK (overflow fitted).

When installing the mixer basin valve, I used the flexi hoses with isolation valves built in. Can they reduce the flow rate?

Is there a way to fix this or should I go back to stand alone taps. I could put pressure reducing on COLD TAP but how to get the HOT WATER back to its original flow rate?

OR should I feed the HOT WATER from the pump.

The hot water flow rate in the kitchen sink (mixer tap) is also not very good. What I've also noticed is that the OLD ball valve in the header tank is slower to fill the header tank compared to the New ball valve in my cistern. Not sure if it matters though in this situation.

Thanks for yout help in advance..

 

[tamz]

Pressure balancing valve, better known as an equalising valve.
Such as this
Pressure Equalising Valve - Plumbworld available at Plumbworld

but it won't be of any use as his hot pressure is about 0.05 bar at the tap

 

[ksareen]

tamz, please refer to my post before. I am going to increase the HOT WATER pressure by giving it the output from my bath's shower pump (single negative head). So I expect the HOT WATER pressure to be little more than 0.05 bar 😉
Thanks

WHPES
Thanks for the link. I like the pressure balancing valve that Tamz mentioned more than pressure reducing valve. I've fed hot and cold feeds using flexi hoses with built in isolating valves.
Looking at the pics on screwfix for double check valves, they look so similar to isolation valves, which my flexi hoses are built with anyway. In fact I am adjusting the flat screw on the iso valve on the flexi pipe to lower the mains cold pressure.

If there is a difference between iso valve and double check valve (Both seem to have directional arrows on them), please let me know.

 

[WHPES]

Yes, different thing totally. DC valve is a form of non-return valve. With your type of mixer tap, this is a legal requirment on the cold feed. Don't tamper with the nut on a DC valve or the thing will fall to bits!

 

[tamz]

If you are going to pump the hot, the equalising valve will be fine.
A double check valve has 2 plastic seals held in position with small springs. They only allow water to pass in one direction (as shown by the arrow). The water pushes on the seal and the spring allows it to move back and let water through. If you fit it the wrong way around the water pushes the seal shut. The screw in the middle is for test purposes to confirm that it is still acting as a double check with both seals functioning as they should. A single check valve has only one seal inside and no test point. You can use 2 singles one after the other, instead of a double.

 

[ksareen]

WHPES, TAMZ, thanks for the load of info. You guys rock.

P.S. I think double check valves are very useful the way you describe. I am going to install them on all mixers (bath, tap and shower) on both HOT and COLD feeds.

 

[WHPES]

Don't do that. Completely unnecessary on the hot and the shower will already have integral ones present in the mixer. They are only to comply with the water regs in the event of a fault and do not have any usefeulness in normal operation.

 

[ksareen]

The reason for doing both HOT and COLD was that at the moment, when using both taps (as mixer), the cold is pushing HOT water back into the copper cylinder and into the header tank. DC valve would stop that.

But you are right. When I would install pumped HOT and equalising/ balancing valve, then I won't need DC on the HOT pipe.

Thanks once again.