It's evident that chamber isolation valves should close on power failure, but the automated behavior of the cryopump was a surprise problem. It would be wise to label critical valves. Attempts to service operating equipment in the interests of haste should be resolutely resisted. And, automated behavior in equipment should be looked at with a very skeptical eye. In fact, both mbe systems now run for extended periods in which they are intermittently unattended.
Nature enforces the law of unintended consequences with much glee.
Liquid nitrogen can run out, as it did over the 4th of July weekend, power can be lost as happened recently in LeConte. Pumps can quit for a variety of reasons, including but not limited to human error. However, the power failure of the 23rd revealed first that the valve controls worked correctly and second that the valve now leaks at the gate seal. The surmise is that the same arsenic which coated the windows when the ln2 supply ran out also coated the valve seats. The leak is big enough to overwhelm the growth chamber ion pump so any pump failure will eventually force the system to shut down.