In article , John Armstrong
writes
On Sun, 26 Oct 2003 18:05:31 +0000, Mark wrote:

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)

I think you have the wrong sort of tap, which is only suitable for high
pressure (ie combi) hot water systems. As others have said, the non return
valve is to stop contamination of the main cold water because the water is
mixed in the body of the tap rather than at the end of the spout.
Since your hot water is gravity fed, if you open hot and cold taps at the
same time, the higher pressure mains cold will push the lower pressure hot
water back up the pipe.
I don't know whether putting the valve on the hot side would physically
work (if the valve is designed for mains pressure to operate it) to stop
the cold going back up into the hot, but the difference in pressure is
likely to stop much hot water coming out of the tap when the cold is on. It
wouldn't comply with Bylaw 30 though.

Good points, nothing on the tap box to say full pressure systems only,.

Water is definitely mixed in the body of the tap (if I had know this I
wouldn't have brought it)

must make sure that I remember to run tap on full cold first before
taking drinking / cooking water, and slow time find another tap her
indoors likes (that doesn't, mix the water inside)
--
Mark