Understood. There is certainly no user adjustable OPV in the Astra as it comes from the manufacturer. Granted, there could be a non-adjustable OPV or ultimate safety valve, but I haven't found it. I'm an engineer, but not a Mech E, so it's very possible I missed something in going over the path of flow from pump to group head. However, the only branch off of the flow path that I found is the deaeration valve. I don't know where any vented pressure would go.

True, 16 bar may only represent a danger to a good shot; for all I know the machine is designed to withstand many times this. However, I do feel better knowing I can limit what pressures the machine sees.