High pressure oil from the pump is directed by the control valve through port (A) to fill the cylinder. Any air in the hydraulic system will be trapped in the end of the cylinder (B) and may be bled off through the bleeder valve (C). It is advisable to bleed air from the cylinder on initial start up and on a weekly basis thereafter.

As the system pressure rises, the oil pushes on the bottom of the largest plunger (F) forcing it to move out. The outside diameter or sealing area of the plunger (D) determines the effective area.  

As the plunger extends, the oil trapped between the plunger wall (E) is released through internal port holes in the plunger. When the largest stage is fully extended, the next largest will proceed to extend, etc.