We lost instrument air pressure at the Corner Station for several hours today as others were replacing the compressor units.  I had isolated the pneumatic pistons (closed 1/4 turn valves) for GV6 and GV8 prior to the loss of air pressure so as to minimize the stroking of the lead-screw belows but GV6 eventually sagged and the MEDM screens indicated a YELLOW status nonetheless.  I reopened these isolation valves and fully stroked open GV6 and GV8 upon the return of air pressure following the compressor work. 

Additionally, I had substituted bottled N2 in place of the instrument air line so as to maintain functionality of the electro-pneumatic isolation valve used on the HAM6 turbo backing cart so as to continue pumping HAM6 uninterrupted during the compressor replacements.