Hydraulics Systems Flashcards
Purpose of Hydraulics
Converts pilot muscle power into forces required to operate aircraft systems
- In large aircraft the forces required are large
Hydraulic Power
Determined by:
- System pressure (pressure is felt equally on all surfaces in an enclosed space
- Volume flow
Workings of Hydraulics
Transmits power by moving an incompressible fluid from one place to another
Can be active (electrically driven pump) or passive (hand pump)
Characteristics of Hydraulic Fluid
Thermal Stability Low emulsifying (doesn't froth) Corrosion resistance High flash and fire points Low compressibility Low viscosity Low volatility Compatible with other material (prevents deterioration of seals)
Types of Hydraulic Fluid
Vegetable oil
Mineral oil
Phosphate ester base (synthetic)
Cannot be mixed
Vegetable Oil
Straw
Natural
Natural rubber seal
Mineral Oil
Red
Synthetic rubber seals
Phosphate Ester Base
Purple
Synthetic
Butyl rubber/teflon seals
Passive System
If an internal leak occurs the temp of the fluid will rise (fluid seeps past a broken seal)
Non-return valves
Pumps both ways
Components of a Passive System
Pressure line (made of steel)
Return line (made of aluminium alloy): returns oil to the reservoir
Case drain lines/fluid coolers
Hydraulic motor
Active System Components
Reservoir
Emergency shut-off valve
Pumps
Reservoir
Allows for variation in fluid volume being returned
Allows for expansion of fluid due to an increase in temperature
Emergency Shut-Off Valve
Isolates hydraulic system in the event of a system failure, engine failure or fire
Cut Out Valve
Allows fluid to return to the reservoir once the pressure in the system has been reached (constant volume pump doesn’t know when to stop)
A constant pressure variable stroke pump uses a pressure control piston to push the swash plate straight and prevents pumping when the pressure is sufficient
Accumulator
Keeps the system under pressure
