What materials form the bases of the three types of hydraulic fluids?
Vegetable (MIL-H-7644 Blue Vegetable Base)
Mineral (MIL-H-5606 Red Kerosene/Petroleum Base)
Phosphate-esters (Skydrol Purple Phosphate-ester Base)
What colors denote mineral-based and phosphate-ester based hydraulic fluids?
Mineral based fluids are red
Phosphate-ester based fluids are light purple
What are the results of exposing lacquers, oil-based paint, and plastic resins, and vinyl compounds to phosphate-ester based hydraulic fluid?
The materials will be damaged and/or softened, or the paint will peel
Name several sources used to develop hydraulic pressure.
Hand pumps, engine- driven pumps, and electrically driven pumps
What would cause the bypass valve in a hydraulic filter to open and allow unfiltered fluid to circulate in the system?
A clogged filter element
Describe several methods of pressurizing a hydraulic reservoir.
Engine bleed air,
system pressure acting on a small piston in the reservoir,
using variable-displacement hydraulic pumps
What feature prevents engine damage if an engine-driven hydraulic pump seizes or is overloaded?
A shear section in the pump driveshaft will break, disconnecting the pump from the engine
Describe the purpose of a pressure relief valve.
Pressure relief valves limit the maximum pressure produced by the pump, thereby preventing failures of the system components
Engine-driven pumps deliver the output fluid flow in what two forms?
As a constant volume or a variable volume
Describe the operation of a gear-type pump.
Two meshed gears, driven by a power source, rotate in a housing. Inlet fluid is carried around the outside of the gears and delivered to the outlet side as the gears rotate
Describe the purpose of the pressure regulator.
Pressure regulators manage the output of the pump to maintain system pressure. They allow the pump to be unloaded so it turns without significant resistance
What is the device that is used in some systems to supplement the pump output during periods of high demand?
What are the three different types of accumulators?
Piston, diaphragm, and bladder
What safety precautions must be taken prior to disassembling an accumulator?
Release all of the air or preload
When a hydraulic unit is replaced, what precautions should be taken to avoid contamination of the system?
All lines should be capped or plugged immediately after they are disconnected
What types of components or systems are pneumatically operated in some aircraft?
other mechanical actuators
Name several sources of pneumatic power
Storage bottles, engine bleed air, engine-driven compressors or vane-type pumps
What happens to excess pressure in a pneumatic system?
A relief valve vents it overboard
What is the function of a restrictor in a pneumatic system?
To control the rate of flow of the airflow
What are the reasons for periodically purging a pneumatic system?
To remove moisture and contaminants