Airframe Systems & Components: Hydraulic & Pneumatic Systems 🔊 Flashcards
What are the three principal categories of hydraulic fluids?
Mineral (5606), polyalphaolefin (83282), and phosphate ester (skydrol)
What is the color of mineral based hydraulic fluid?
red
How do you determine which type of hydraulic fluid to use in a specific system?
It is specified in the Aircraft Maintenance Manual or on the instruction plate attached to the reservoir on the unit being serviced
What will happen to the seals in a vegetable base hydraulic system if it is serviced with mineral based or phosphate ester based fluids?
Seals will swell, break down, and block the system
When installing a chevron seal what must be considered?
It is directional and must be installed with pressure going toward the open side of the seal
When hydraulic lines have been disconnected, what precautions should be taken to prevent contamination of the system?
They should be capped or plugged immediately after disconnecting
What happens to the hydraulic fluid flow if the filter element becomes clogged with foreign matter?
There is a bypass valve which routes the hydraulic fluid directly from the inlet port to the outlet port
What is a micronic filter?
A paper element filter
Name the filters used in aircraft pneumatic systems.
Paper pleated and screen type
Why are some hydraulic reservoirs pressurized?
To ensure a positive flow of fluid to the engine driven pump at high altitudes
What methods are used to pressurize hydraulic reservoirs?
Some systems use a variable displacement hydraulic pump, engine bleed air, or hydraulic system pressure acting on a small piston inside of a reservoir. Another method is an aspirator or Venturi.
What are two types of accumulator housings?
Spherical or cylindrical
Name three types of hydraulic accumulators.
Diaphragm type, bladder type, and piston type
What is the purpose of a pressure relief valve in a hydraulic system?
It is to limit the amount of pressure in the system
What is the purpose of an unloading valve in a closed hydraulic system?
It is designed to provide a low-pressure path for the fluid to flow from the pump back to the reservoir when the system has no flow requirements
What is the function of a wing flap overload valve?
It prevents possible structural damage to the flaps or the flap system that might result from the flaps being lowered at excessive speeds
What is the purpose of the shear-able section in a hydraulic pump?
If the pump were to seize, the shear section will disconnect the pump from the engine, allowing the engine to continue to operate
What are two different types of hydraulic pumps?
Hand pumps or power pumps, also classified as positive displacement or non positive displacement
What pump is most suitable for low pressure pneumatic systems?
A vane type pump
What protects a direct pressure type hydraulic pressure gauge from pressure surges?
A dampening device in the form of a very small restrictor is installed in the line leading to the gauge or at the inlet to the gauge itself
What are pneumatic systems used for in aircraft?
To operate brakes, open and close doors, starting, pump driving, and operating emergency devices
What happens to the air after a pneumatic system is operated?
The air is dumped overboard
Why should a pneumatic system be purged periodically?
To remove contamination, moisture, or oil from components and lines
What is the purpose of the relief valve in a pneumatic system?
It protects the system against over pressurization (thermal expansion) by venting excess pressure to the atmosphere
What is the purpose of an accumulator?
They are used to prevent hydraulic system shock when under high load demand conditions
What would cause a hydraulic filer to go into full bypass mode allowing unfiltered fluid into the system?
A clogged filter
