Resumed XBM pump down today by valving the QDP80 back in. At about 500 mTorr, spun up turbo and pressure fell to mid -4 Torr range within a few hours.

Needed custom adapter cable used at XBM for YBM turbo to start its pump down (for safety valve engagement) and in the process of swapping cables at XBM turbo station, the QDP80 tripped. Scroll was running and turbo was in local mode, anticipating a trip, but I forgot to close the QDP80 manual valve, so there was some backstream flow that caused the turbo to trip from overpressure. Thankfully the 10" isolation gate valve was closed the entire time, so the main volume pressure was not affected. Turbo volume pressure rose to about 10 Torr.

Upon start up after incident, the turbo pump tripped from strong vibration and won't come up to full speed. We tried several the tricks including feeding a gas load at inlet to load the bearing. This turbo has a history of failing from rotor resonance and in the past front loading with gas has helped. May the XBM Seiko rest in peace.

Pressure in XBM is currently reading 2e-4 Torr. We could leave it sit until we start pumping on adjacent vertex volume next week, by opening GV2 and combining volumes, or make an effort to:  a) install old turbo that was just removed from vertex or SS500b; or b) install new turbo station, untested (scheduled to replace this turbo in third week of vent). Will sleep on it and see how pressure rises overnight.