Basic Hydraulic System

In the basic hydraulic system, as shown below the basic components that all hydraulic systems may consist of, 

Actuator

Sometimes referred to as a hydraulic jack, this provides the output force required to operate various aircraft services.  Consists of a piston,on which the hydraulic pressure acts, which is secured to a rod, also known as a ram, which imparts the force developed by the piston.

Selector 

This component provides control of the system, and may be manually or electrically operated from the cockpit.  The terms ‘pressure’ and ‘return’ may only be applied to pipelines up to this component, the pipelines from the selector to the actuator may be referred to by their purpose ex: UP/DOWN,OPEN/CLOSE,RETRACT/EXTEND

Pump

The pump provides a flow of fluid to the system.  its should be mentioned pump provides flow, not pressure, as it is the resistance to that flow that causes a pressure rise,without making a resistance to the flow the pressure cannot be created.  In the illustration a simple hand pump is shown, many aircraft systems use engine or electrical motor driven pumps to provide greater flow rates and so speed up system operation.

Reservoir

The reservoir provides a means of holding surplus fluid, its purpose is to receive, store and supply fluid to and from the system.  It maintains a surplus, so that in the event of a leak the system will still have sufficient fluid to operate correctly.

It stores fluid that is temporarily not required by the system, as can be seen the actuator does not have equal volumes on each side of the piston.  When retracted (piston rod fully into the body) the actuator will hold less fluid than when fully extended (piston rod fully out of the body) and so this fluid must be stored when not in use.

The reservoir will also supply fluid to the pump to maintain a flow within the system and receives return fluid from the system.

Pipelines

The system pipelines are used to direct fluid to the appropriate components.  They may be made from various materials depending upon the pressure at that point in the system and the operating environment.  Within the system they are normally referred to by the nature of their oil flow ie. RETURN LINE or PRESSURE LINE.