Kyle, Gerardo, John

Had valved-out QDP80 pump from YBM before leaving last night.  YBM pressure was 20 torr at that time.  Pressure rose to 200 torr in ~18 hours, i.e. large unexplained gas load in YBM volume -> Resumed pumping YBM with QDP80 this morning.  Pumped adjacent annulus volumes (BSC8, GV1 and GV3-GV5 already under vacuum).  Connected leak detector in parallel with QDP80 pump path and set detector up for high pressure leak testing (10 torr max inlet pressure).  Once YBM pressure reached 10 torr, Gerardo and I did a "rehearsal" exercise by spraying some feed-throughs on BSC8 -> Noticed a large delayed response after tens of seconds.  Time constant believed to be around 1800 seconds for these conditions.  Signal continued to rise for ~30 minutes after initial (10 sec/flange dwells) until signal "railed" the leak detector at 9.9 x 10-4 torr*L/sec. -> Surprisingly, Gerardo was unable to find this "wopper" leak by utilizing the stethoscope!  We probably could hear this leak with our unaided ear if there wasn't so much background noise in the LVEA. -> For tonight, I am leaving the YBM vent/purge valve "cracked" open a little so as to keep a viscous stream flowing in the correct direction in the event of a QDP80 stoppage during the night.  This way we won't have to valve-out the pump overnight and we can resume leak testing in the morning without having to wait "hours" to get back to 10 torr.