The non return valve is normally on the cold side, so that water from the
tank cant get into the mains water.

If the mains fails, water could get into it if both the taps are turned on &
there is no non return valve.

Better taps have a dual spout & doesn't need this, the water mixes out of a
closed vessel.


--
regards
Dave Batter
Kitchenman
www.kitchenman.co.uk
www.sxmitres.info
www.marks-family.co.uk
http://oneandone.co.uk/xml/init?k_id=5568652
"Mark" wrote in message
...
Just purchased a replacement kitchen tap, that came with a bylaw 30 kit
(look like a one way valve for the hot side (red arrow))

Q. do I need to fit this?

Mains cold water and gravity hot water (cold storage tank in loft)

--
Mark