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?

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

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

- 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?

thanks for any comments,
Andrew