thermmech,
I understand the OEM's recommendation regarding the valves being installed in the reverse (incorrect) orientation downstream from the filter vessels. Same issue exist for valves with a preferred high pressure side on pump discharge isolation. When the pump is down for maintenance...
Anarchy
From the manual of a well known Instrument supply regulator company it states "other overpressure protection must be provided if inlet pressure can exceed the maximum pressure rating of downstream equipment or exceeds maximum outlet pressure rating of the regulator". This applies to...
I know two valve manufacturers which make a Ball valve similar to your description.
Jarecki Valve's Phantom Port Ball valve (Floating design) and Newmans-Newco Valve's QuadroSphere Ball Valve (Trunnion design).
Hope this Helps.
Rich