Hydraulic and Pneumatic Power Systems How would the air pressure charge in the accumulator be determined if the engine is inoperative, but the system still has hydraulic pressure? a. Read it directly from the main system pressure gauge with all actuators inoperative. b. Build up system pressure with the emergency pump and then read the pressure on a gauge attached to the air side of the accumulator. c. Operate a hydraulic unit slowly and note the pressure at which a rapid pressure drop begins as it goes toward zero.