PT170 and PT180 were installed in March 2016 when the X/Y beam manifold volumes were vented. PT140 was installed in Sept. 2016. Attached is trend from time of installation. Looks like PT170 & PT180 have been drifting up since after closing and re-opening isolation GVs 5/7 for HAM6 vent. We burped in accumulated gas from gate annuli but I'm not sure what the second hump is from April 9th. No log entry found.