I don't feel comfortable with the degree to which GV5, GV7 and GV20 are "soft-closed" for the unattended worst case scenario -> Switched YBM turbo from being backed by its QDP80 to the safer state of being backed by the LD which has its own, redundant, energize-open isolation valve -> valved-out XBM turbo 

The solenoid-actuated air manifold which switches instrument-air from either the bottom or the top of GV7's piston leaks unpredictably when the applied air pressure is low, i.e. with the nominal 5 psig applied when GV7 is soft closed.  For instance, if the regulator is isolated from the manifold and an output of 5 psig is selected this pressure falls to 0 psig when valved-in to the manifold and stays 0 psig regardless of how much time elapses.  If the applied pressure is increased the audible "hissing" past the leak increases but the piston pressure remains 0 psig - to a point. If the regulator output pressure is further increased eventually the pressure at the piston will "come on scale" but the leak rate will often change simultaneously and then the desired pressure applied to the piston will be exceeded and GV7 may cam hard-closed etc. (GV5 doesn't do this)

I moved the newly assembled scroll pump+sentry valve+relay box assembly out to the X-end station and am running it in standalone mode to get some hours of running on it before using it in place of the X-end turbo's QDP80 -> Once in use, the failure mode for the X-end turbo will have two layers of protection.