Follow the hydraulic system · Free Commercial Pilot Lesson

How the system moves the rod

How hydraulic pressure moves a mechanism

Pressure enters the left side. The piston pushes the rod outward while fluid from the right side returns to the reservoir.

Follow the pressure and the return

Pressure to the cylinder

Return to the reservoir

P: pressure supply. R: return. A and B: the two cylinder lines.

1 · Cylinder. A sealed piston and rod move together.
2 · Selector. Routes pressure and return to opposite sides.
3 · Reservoir. Supplies fluid and receives the return.
4 · Pump. Supplies the flow that moves the piston.
5 · Filter. Keeps contamination out of the fluid.
6 · Relief valve. Closed here. Opens if pressure is excessive.

Starts only when you choose.

Representative double-acting actuator. The gear linkage, indications and extension procedure depend on the airplane. This illustration does not model actual pressure, speed or end-of-stroke behavior.

Sources for this illustration

FAA Aviation Maintenance Technician Handbook—Airframe (2023), pages 12-5–12-6, 12-27 and 12-32–12-33; Figures 12-52 and 12-53. Gear indications: page 13-23.

FAA Pilot’s Handbook of Aeronautical Knowledge, Chapter 7, pages 7-31–7-34.

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A hydraulic system transfers power through fluid. In the system shown here, a reservoir supplies the pump, a selector valve directs the flow, and an actuator turns hydraulic power into movement.

This is a conceptual double-acting actuator. It teaches the fluid paths; it is not the plumbing, timing or operating procedure for a specific airplane.

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