On Tue, 7 Jul 2020 09:45:23 +0100, 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?

AFAIK 1 bar is 10m of head,

Yep.

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? I'd be surprised if that is
above 10 bar. There are hi/lo limits to supply pressures. Water
pressure guages are cheap in the sheds...

--
Cheers
Dave.