Chapter Objective: Upon completion of this chapter, you will have a working knowledge of the components of the basic actuating systems and their related maintenance procedures.

The actuating systems consist of the hydraulic components used to direct and control the flow of pressurized fluid as well as the components used to perform the actual work. This chapter begins with a discussion of actuating units, and covers most of the various actuating system components that are used in modern-day hydraulic systems.

An actuating unit may be defined as a unit that transforms hydraulic fluid pressure into mechanical force, which performs work (moving some mechanism). Two types of actuating units are used in naval aircraftactuating cylinders and hydraulic motors. Both types are discussed in this chapter.

Actuating cylinders are the most commonly used actuating units in aircraft hydraulic systems. The purpose of an actuating cylinder is to convert fluid under pressure into linear or mechanical motion. Actuating cylinders are generally installed in such a manner that the piston shaft (rod) end of the cylinder is attached to the mechanism to be actuated, with the other end attached to the aircraft structure.

There are two types of actuating cylinders balanced or unbalanced. Balanced actuators have equal working areas, with a piston shaft extending from both sides of the piston head. This type of cylinder may be a single-acting actuator, which receives hydraulic pressure on only one side of the piston head for movement in one direction, and some other means of force for movement in the opposite direction. However, it may also be a double-acting type, which uses hydraulic pressure alternately on both sides of the piston head to move it in the selected direction.

The most common type of actuating cylinder used on naval aircraft is the unbalanced type, which maybe either single or double acting. Unlike the balanced actuator, it has a single piston shaft extending from the piston head, resulting in unequal working areas. Each actuator used may differ considerably in size and construction.