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Hydraulics & Pneumatics

Introduction:

Pilot Handbook of Aeronautical Knowledge, Basic Hydraulic System
Pilot Handbook of Aeronautical Knowledge,
Basic Hydraulic System
Pilot Handbook of Aeronautical Knowledge, Basic Hydraulic System
Pilot Handbook of Aeronautical Knowledge,
Basic Hydraulic System

Hydraulics

  • A basic hydraulic system consists of: [Figure 1]
    • Reservoir
    • Pump (either hand, electric, or engine driven)
    • Filters to keep the fluid clean
    • Selector Valves
    • Relief Valve
    • Accumulators
    • Actuators
  • Hydraulic Reservoir:

    • A mineral-based hydraulic fluid is the most widely used type for small aircraft
    • This type of hydraulic fluid, a kerosene-like petroleum product, has good lubricating properties, as well as additives to inhibit foaming and prevent the formation of corrosion
    • It is chemically stable, has very little viscosity change with temperature, and is dyed for identification
    • Since several types of hydraulic fluids are commonly used, an aircraft must be serviced with the type specified by the manufacturer
  • Hydraulic Pumps:

    • The hydraulic fluid is pumped through the system to an actuator or servo
  • Hydraulic Servos:

    • A servo is a cylinder with a piston inside that turns fluid power into work and creates the power needed to move an aircraft system or flight control
    • Servos can be either single-acting or double-acting, based on the needs of the system
    • This means that the fluid can be applied to one or both sides of the servo, depending on the servo type
    • A single-acting servo provides power in one direction
  • Hydraulic Selector Valves:

    • The selector valve allows the fluid direction to be controlled
    • This is necessary for operations such as the extension and retraction of landing gear during which the fluid must work in two different directions
  • Hydraulic Relief Valves:

    • The relief valve provides an outlet for the system in the event of excessive fluid pressure in the system
    • Forces exert equal pressure on system
    • Input smaller than output increases force
    • Pumps provide system pressure
      • Variable
      • Constant: pressure regulators control pressure
    • Pressure gauges provide a way to monitor the system
    • Relief valves return fluid to the reservoir
    • Check valves used for 1 way flow
  • Hydraulic Accumulators:

    • Accumulators provide shock absorption for 1 time use

Conclusion:

  • Each system incorporates different components to meet the individual needs of different aircraft

References: