Initial view: This is a rack of hydraulic power accumulators. Inside each cylinder is a floating piston. On the side of the piston closest to the camera the accumulators are filled with hydraulic oil . The other side is filled with high-pressure nitrogen gas.
To charge the system a pump forces oil into the accumulators and pushes the pistons toward the other end, compressing the gas on that side. When the pistons reach the far end the pump shuts off and valves are closed to hold the pressure in the system. This is the equivalent of cocking a gun. To open the silo door, valves on the oil side are opened. This relives the pressure on the oil side and permits the high-pressure gas on the far end to push the oil out of the cylinders, through a system of pipes, and into the motor on level 1A. There is enough accumulated energy in the cylinders to operate the door through one and a half full cycles (open-close-open). This system permits the door to operate without benefit of electric power—sure to be lost quickly in a nuclear war.