Preshift Exam No. 1 Taken from the 2016 Alabama State Preshift Contest held in Sumiton, AL Progress Indicator: Question 2 of 10 2.  BG-4 minimum valve activates between ________ and ________ mbar. Choices: 1 and 2 .1 and .2 .1 and 2.5 1 and 2.5