Dave Liquorice wrote:

Andy Burns wrote:

But when connecting the PRV, I can't get any get flow out of it

Lets start with the obvious, got the direction of flow right?

Yes, it has an arrow on the outlet :-)

any reasonable way to estimate the supply pressure?

I don't think so short of having a pipe rising up to the point where
the flow stops. Anything with a flow is going to drop the pressure
dependant on how much flow and the resistance to that flow there is.

Is this supply the normal water mains?

Yes.

I'd be surprised if that is above 10 bar.

Having had a look at pressure gauges, and other PRVs they do seem to
top-out at 10 or 11 bar, I'll buy a gauge.