M11.11 Flashcards
What are the two types of hydraulic pressure?
Hydrostatic pressure - This is the pressure produced by static or nearly static fluids. Hydrostatic pressure is the type of pressure used in an aircraft hydraulic system.
Hydrodynamic pressure - This is the pressure produced by moving liquids ideally with no internal friction.
What are the basic system layout if hydraulic systems
Reservoir
Motor-driven pump
Hand pump
One-way check valve(s)
Pressure relief valve
Directional/selector valve
Actuator
Filter
PTU power transfer unit
PTUs have a fixed displacement while others use a Variable Displacement Pump (VDP)
PTUs in aircraft allow component operation in a hydraulic system in which the pump has failed.
two units, a hydraulic pump, and a hydraulic motor are connected via a single drive shaft so that power can be transferred between two hydraulic systems. Their is no fluid transfer its mechanical
What does ACMP stand for and when is it used
Alternating Current Motor Pumps or Electrically-driven hydraulic pumps
mechanically connects to a hydraulic pump
They can be a primary source or emergency source of hydraulic pressure
Can be used after takeoff to supplement
The motor can get hit and is cooled by air to help
What is a hydraulic power pack system?
a compact unit that consists of an electric pump, a reservoir, valves, filters, and a pressure relief valve all in one assembly.
What are the advantages of the hydraulic power pack system?
No need for a centralised hydraulic power supply system and long stretches of hydraulic lines. This reduces weight.
Integration of essential valves, filters, sensors, and transducers virtually eliminates any opportunity for external leakage and simplifies troubleshooting
What are hydraulic power packs driven by?
Power packs are driven by either an engine gearbox or an electric motor.
What are the properties of hydraulic fluids?
Low flammability
Corrosion resistance
Good lubricating quality
Resistance to freezing
Non-evaporating
Non-foaming
Chemical stability
Hygroscopic quality
Viscosity of hydraulic fluids?
hydraulic system must have enough body to give a good seal at pumps, valves, and pistons, but it must not be so thick that it offers resistance to flow
A fluid that is too thin also leads to rapid wear of moving parts or of parts that have heavy loads.
The instruments used to measure the viscosity of a liquid are known as viscometers or viscosimeters.
What are the three categories of hydraulic fluids?
Minerals
Polyalphaolefins
Phosphate esters
What is important when refilling a hydraulic system?
the engineer must be certain to use the correct category of replacement fluid. Hydraulic fluids are not necessarily compatible.
Mineral based hydraulic fluids
The oldest dating back to 1940
It is used in many systems, especially where the fire hazard is comparatively low
interchangeable and can be mixed together. It has an odour like penetrating oil and is dyed red.
MIL‑H‑6083 rust-inhibited version
MIL‑H‑5606.
Polyalphaolefin-based hydraulic Fluids
MIL‑H‑83282 is significantly more flame resistant than MIL‑H‑5606
high viscosity at low temperatures is a disadvantage
MIL‑H‑83282 is a fire-resistant hydrogenated polyalphaolefin-based fluid
1960s
Phosphate Ester-based hydraulic Fluid
Skydrol®
used in most commercial transport category aircraft and are extremely fire-resistant. However, they are not fireproof and under certain conditions, they burn.
types IV and V fluids are used.
What are the 2 classes of Skydrol
Class I fluids are low density
Class II fluids are standard density
The class I fluids provide weight savings advantages versus class II
Mixing hydraulic fluids
petroleum-based and phosphate ester-based fluids will not mix
the seals for any one fluid usable with or tolerant of any of the other fluids
If an aircraft hydraulic system is serviced with the wrong fluid type, immediately drain, and flush the system and maintain the seals according to the manufacturer’s specifications.
What paints are skydrol resistant
epoxies and polyurethanes
What are the two types of hydraulic fluid contamination?
Abrasives (including such particles as core sand, weld spatter, machining chips, and rust)
Non-abrasives (including those resulting from oil oxidation and soft particles worn or shredded from seals and other organic components)
How do you check for hydraulic fluid contamination?
liquid samples should be taken from the reservoir and various other locations in the system.
What are the 2 main servicing activities on hydraulic systems
Reservoir filling
Fluid sampling
