Diesel Law Exam No. 3 Questions taken from the Pennsylvania Bituminous Mine Officials Exam Study Guide Progress Indicator: Question 4 of 15 4.  The check valves in hose adapter perform a critical function.  Which of the following is NOT true? Choices: They control the directional flow of inhalation and exhalation gasses. They control the amount of oxygen being metered out from the oxygen cylinder. The inhalation valve is closed during exhalation. The exhalation valve is closed during inhalation.