Actuator having dual piston surfaces

A pressurized-fluid-operated actuator has two piston surfaces for providing increased output force. The actuator includes a hollow piston that is divided into two inner chambers by a stationary inner dividing wall that is rigidly connected with a cylinder end wall. The piston has an outer diameter that is smaller than the inner diameter of the cylinder, and the piston carries three axially spaced sealing rings that define two axially-spaced annular chambers between the piston and the cylinder. Each of the annular chambers is in fluid communication with a respective port provided in the cylinder wall. Introduction of pressurized fluid into one port causes the fluid pressure to act on a single piston surface to retract the piston and rod, and introduction of pressurized fluid into the other port causes the fluid pressure to act on two axially-spaced piston surfaces to provide an increased output force without increasing the diameter of the cylinder and piston and without increasing the pressure of the fluid.