IFP
Well my manuals talk of 'Dual Shuttle Valves' so I assume Airbus know they exist! However your inference that I'm barking up the wrong 'valve tree' is correct !!
The valve that has had most problems in this area is the Parking Brake Operated Valve.
I have a magnificent diagram with cross sections of all the valves but no way of posting it!
Will PM to anyone that requests it!