The earliest aircraft had simple controls that were operated manually. Today's jet aircraft can have numerous systems that work together to keep a plane in the air and to help it land. A jet's hydraulic system is one of the most important systems.
Jet aircraft hydraulic systems use pressurised fluid to perform physical work. Hydraulic pumps create fluid flow that pressurises the system's hydraulic fluid. The pressurised fluid is routed to motors and actuators that operate various mechanical parts.
In-flight hydraulic systems are primarily run by engine-driven pumps operated by the rotation of the jet engines. Electric pumps can be used to pressurise systems on the ground, and many jets have hand-operated hydraulic systems for emergency situations, such as extending landing gear during a loss of normal hydraulic pressure.
A typical jet hydraulic system pressurises liquid to 1361 Kilogram per square inch (psi). This pressure effectively operates motors that run flight controls, move gun turrets, raise landing gear, and operate cargo doors among other functions.
Every jet's hydraulic system needs a fluid reservoir to store the systems hydraulic fluid. Pumps create fluid flow that ultimately leads to system pressure; actuators and motors perform the actual work in a hydraulic system. The systems also use various control valves to route fluid through tubing and hoses on its circulatory trip through the system.