Hydraulic and Pneumatic power systems Flashcards
What are the three principle categories of hydraulic fluids?
- Mineral (5606). 2. Polyalphaolefin (poly alpha olefin) (83282). 3. 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?
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?
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?
All lines and fittings 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.
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.
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 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 to the reservoir when the system has no flow requirements. The unloading valve also acts as a
pressure regulator.
What is the purpose of the shearable section in a hydraulic pump?
The shear section will disconnect the pump from the engine, allowing the engine to continue to operate.
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 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.
For What purposes are pneumatic systems used in some 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.
What is the purpose of a pressure relief valve?
To limit the amount of pressure, thereby preventing failure of the system components.
What is the purpose of an accumulator?
Accumulators are used to prevent hydraulic system shock when under high load demand conditions.
What is an example of a phosphate ester base fluid?
Skydrol.
What happens to plastic resins, vinyl compositions, lacquers, and oil base paints if exposed to a phosphate easter base hydraulic fluid such as skydrol?
The material will be damaged, softened and/or peeled.
What precautions should be taken to minimize contamination during replacement of a hydraulic unit?
All lines should be plugged or capped after disconnecting.
What are two types of engine-driven hydraulic pumps?
Constant-delivery and variable-delivery.
What are sources of pneumatic power?
Storage bottles, vane-type pumps, and turbine engine compressors.
What happens to the excessive pressure in a pneumatic system?
A relief valve will bleed it to the atmosphere.
What must be accomplished with any accumulator prior to disassembling?
Make sure the air or preload has been discharged.
What feature is built into a hydraulic pump-drive system to prevent engine damage in the event of pump seizure or overload?
A shear section in the pump-drive shaft.
What would cause a hydraulic filter to go into open bypass, allowing unfiltered fluid into the system?
A clogged filter.
What is the purpose of a pressure regulator?
To manage the output of the pump to maintain system pressure and allow the pump to turn without resistance.
What is used in some hydraulic systems to supplement the power pump when several units are operated at the same time?
An accumulator.
What is the purpose of restriction that are used in aircraft pneumatic system?
To control the rate of airflow.
