In an earlier contribution to this discussion,
David Hansen wrote:

On Tue, 07 Mar 2006 19:24:02 +0000 someone who may be David Hearn
wrote this:-

Separate outlet mixer strongly preferred for kitchen sinks and other
potable water applications. The concentric outlet type with the cold
wired to the outer also helps keep the spout cool to touch.

The diagram of the tap included in the 'instructions' shows 2
separate channels with it being open at the spout before going into
the 'flow straightener' (weird name!)

Can you take the piece of black plastic off the spout? If you can
then can you see two water channels in the spout? If you can then I
don't see that a check valve is needed.

I think that, officially, it's probably still required because some fool
could - in theory - put a hosepipe on the tap and block off the other end,
which could send cold water back up the hot feed - or hot water up the cold
feed in the event of a failure of the cold mains.

But it needs a fairly unlikely combination of circumstances to cause a
problem, and is a regulation which I would - and *do* - ignore. Also, if you
have a check valve in the hot supply, it scuppers any possibility of
back-feeding mains into the hot system to clear an air-lock.
--
Cheers,
Roger
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