A differential cylinder has a piston rod on only one side of the piston surface. It has, as a result, two different large effective surfaces: One the one hand the surface on the piston side, which is completely effective, and on the other the rod-side surface, for which only the ring surface is effective. The ratio of the piston surface to the ring surface is referred to as Φ. As a result, under normal circumstances the differential cylinder moves in and out at two different velocities. If the cylinder is operated in the closed control loop, then it will travel in accordance with the velocity specified by the setpoint. more information under www.hydrosaar.de