Many thanks to John Harper for lending his expertise and assistance, this is now up and running.
First I tested the whole assembly connected to an air tank, for leaks, then closed the tap on the tank so just the air in the assembly was there (i.e. it wasn't getting topped up by the tank anymore), it held pressure, so i swung the ball valve... slight loss of 7 bar as that happened but then she held to the decimal. Then ran the purge valve on the tank, still held... then disconnected... and she's holding, to the decimal. In fact she's gone up at tad as the tank has just come out of the boot and gone from night time Bournemouth's 11.3 degrees to Miss England's preferred room temp of 21.0 degrees C.
The whole assembly is on quick fill adapters so i can swap cylinder adapters for different bottles and various other elements I want to test. By building blanking plates for regs etc I can leak test every stage of the rifles, which saves a lot of guess work, because sometimes it might just be a cheap o-ring on a bottle or a washer instead of the gun itself.
I can also shoot with this attached and see where there's any oddness or consistency in the pressure range as I shoot, and I can get an accurate idea of consumption, by knowing the volume of the cylinder and taking a guess of that of the assembly. With that i can compare then rifles, and say different setups of those rifles.
For those that are wondering why a digital gauge, well we've found that parallax error when reading them can add a variable, and some even change their reading as you hold them different ways. We're trying to dial out the "i think it's doing this" and get to the "I know it's doing this".
We've got a really gucci one on the reg tester which is showing some very interesting stuff. More on that soon.
Anyway, that's me geeked out for today.