Mick,

I don't have them right now in front of me, but if i am not mistaken, port 1 is the inlet (air in) port 2, the output (air out to brakes) and port 3 is the outlet.
During various tests, have also fitted a reducer on port 3 (outlet) but the only result i got was a delay in releasing brakes...
Could it be that pressure is too high. i was starting at 120 psi but duing the proportional braking pressure goes down rather quickly...