Here is a cutaway drawing of the trunnion assembly, showing the major components. I’ve removed some of the steering head linkage for clarity. The unit is an air/oil spring, with air pressure acting as the spring, and hydraulic fluid being forced through orifices to act as the damper. In addition, the steering bellcrank on top turns a steering “blade” that passes through the stanchion (moving cylindrical part), so that steering input is connected to the nose wheel. The amount of air pressure needed depends on the weight on the nose wheel, and for this airplane it’s no more than about 45 psi in the extended position.