"Andrew" wrote in message
...
The plumbing in my bathroom seems a little unusual - the hot
is supplied via a 22mm pipe from CW tank with about 1.5m
head; the cold is mains pressure via a 15mm pipe.

I would like to keep the cold directly mains fed - but not
surprisingly, the mixer showers don't work very well.

I've thought about fitting a pressure-equalising valve
(one for the whole bathroom, rather than one per shower),
such as https://www.plumbworld.co.uk/344-0000.

Does anybody have any experience with these? Specifically,
do they need any "flow" to work?

See the makers specs for minimum pressure and flow. They sometimes don't
operate too well when the pressure difference is too large.

- if the hot tap or cold tap alone is turned on, will I still get the
expected flow & pressure?

Yes.

- if the cold pressure drops to zero (stopcock turned off), will
I still get any hot flow?

Yes.

- I'm planning to put a double-check valve on the CW input
to the valve as well - is this necessary, or could it cause
problems?

Why?