Hydraulic and Pneumatic systems Flashcards
Hydraulic system liquids are used primarily for what?
to transmit and distribute forces to various units to be actuated.
What are the three principal categories of hydraulic fluids?
Mineral (5606), Polyalphaolefin (poly alpha olefin) (83282), 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?
The type of fluid 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 base or phosphate ester base fluids?
The seals will swell, break down, and block the system.
When installing a chevron seal what must be considered?
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?
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 filter with a paper element.
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 the reservoir. Another method is an aspirator or Venturi.
What are the two types of accumulator housings?
Spherical, and cylindrical.
Name three types of hydraulic accumulators.
The 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?
The unloading valve is designed to provide a low-pressure path for the fluid to flow from the pump back reservoir when the system has no flow requirements. The unloading valve also acts as a pressure regulator.
What is the function of a wing flap overload valve?
The purpose of the valve is to prevent 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?
In the event the pump was 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?
There are hand pumps and power pumps. Pumps can also be classified as positive displacement, or nonpositive 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?
Pneumatic systems are sometimes used 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 the components and lines.
What is the purpose of the relief valve in a pneumatic system?
The relief valve protects the system against over-pressurization (thermal expansion) by venting excess pressure to the atmosphere.
What is the purpose of an accumulator?
Accumulators are used to prevent hydraulic system shock when under high load demand conditions.
What would cause a hydraulic filter to go into full bypass mode allowing unfiltered fluid into the system?
A clogged filter.
What type of hydraulic system has the drive motor, hydraulic pump and hydraulic reservoir all in one unit?
Power pack
