On Sat, 1 Aug 2020 12:20:25 +0100, Chris Green wrote:

Looking at pressure reducing valves available from Toolststion,
Screwfix and such I note that a lot of the reviews say that the
pressure builds up when there's no flow. I.e. the pressure reduction
reduces the pressure available when running a tap or (more to the
point possibly) a shower but when all taps are turned off the outlet
pressure builds up to match the inlet pressure.

Not on the one I have here. It holds the outlet pressure at the set
point pretty well. 2.5 bar IIRC with a supply around 4 to 5 bar.
Washing machine and electric shower share the same cold supply, both
can be used at the same time without any temperature changes from the
shower. There is brief pulse in the shower flow as the W/Mc abruptly
open/closes its valve but that is all.

I need to reduce the pressure to some small waterers (as in things for
animals to drink from) ...

Bear in mind that a PRV is spring biased one way valve. If part of
the system freezes the expansion cannot "escape" up the supply, so it
finds somewhere else, pushes a joint apart, splits the pipe...

The one way valve action can also "trap" water hammer pressure
pulses, which may not be producing an audible bang.

--
Cheers
Dave.