Linear actuators convert flow into linear movement and pressure into force by employing a piston that slides inside a cylinder. The construction of a typical double-acting actuator can be seen in Figure 1 that shows the use of appropriate sliding seals for the piston and rod components. The double-acting feature to provide operation in both directions is not always required as in some applica­tions (e.g., fork lift truck systems) the force from the load is used for retraction. Actuators are also available that have a rod at both ends so that the piston areas are equal in both directions of movement.

End covers
The basic methods of attaching the end covers, or caps, to the cylinder of hydrau­lic actuators include:

1. Screwed to the cylinder. This is the method shown in Figure 1.
2. Tie rods as shown in Figure 2. Welded

Mounting methods
A wide variety of actuator and rod end mounting methods are available to suit the requirements of different applications. Figure 2 shows a flange mounting that is part of the front end cap for locating the actuator rigidly to the machine frame.