Hydraulics, landing gear and brakes

Hydraulics

Pascal's law: pressure in a confined liquid acts equally in all directions, so a small force on a small piston produces a larger force on a larger piston. Airliners use about 3,000 psi (some 5,000 psi) with fire-resistant phosphate-ester fluid, in two or three independent systems.

Parts: reservoir (pressurised to prevent pump cavitation), engine- and electric-driven pumps, accumulators (store pressure, damp surges, give emergency braking), filters, relief valves. A power transfer unit moves power between systems without mixing fluid; a ram air turbine gives emergency hydraulic and/or electrical power, depending on the type.