Hydraulics Flashcards
What is 1 bar in psi?
14.5
What is hydrostatic pressure?
Pressure from exerted by static or almost static fluid.
What is hydrodynamic pressure?
Pressure exerted by moving fluid.
When would a seal (o-ring) be used in a hydraulic system?
Places where different fluid pressures meet (I.e. filter housings)
What is the stages of operation for a hydraulic system? Also give examples of components that are found at each stage?
Storage (reservoir)
Pressurisation (pumps)
User (brakes, flight controls, landing gear)
Return to storage (return lines, case drain heat exchanger)
How many hydraulic systems are normally used on aircraft? Also how are they typically idented?
3 system- left, centre, right.
Idented by colours or numbers
What are the standard features of a reservoir?
Cylindrical shape
Resistant to pressure change
Head of pressure on fluid
Why is a head of pressure applied by the reservoir?
To ensure a positive flow of fluid in the system
Does multiple systems draw from the same reservoir?
No, they each have their own reservoir with the relevant capacity for that system
What are the subsystems under hydraulics?
Main hydraulics
Ram air turbine (RAT)
Hydraulic indicating
Ground servicing
What does the RAT provide for the hydraulic system?
Emergency power
What does the hydraulic indication system show in the flight deck?
System pressure Pump pressure Reservoir pressure Pump temperature Reservoir quantity Valve positions
What type of pumps are the ACMP, ADP, and EDP?
ACMP- alternating current motor pump (electric)
ADP- air driven pump
EDP- engine driven pump
What important component will be fitted to the return lines of a hydraulic system and why?
Filters to catch any debris picked up from the user.
How many pumps are normally on the left and right systems?
1 EDP
1 ACMP
How many pumps does the centre hydraulic system?
2 ACMP
2 ADP
Where are the heat exchangers typically located?
Left and right fuel tanks
How does a heat exchanger work?
By running the return though the fuel tanks, the hot hydraulic fluid will be cooled by the surrounding cold fuel, while transferring some of it’s heat to the fuel to stop it from freezing
How are hydraulic pressures and reservoir quantities displayed?
Pressure- psi
Quantity- percentage
Which systems would typically power the normal and alternate braking?
Normal- right system
Alternate- centre
Which system does the RAT act as an emergency source of pressure?
Centre
Why is a baffle used in a reservoir?
To prevent upward motion of fluid at loss of altitude
To trap some hydraulic fluid at the bottom to ensure a positive fluid supply
What can be prevented by pressurising the fluid in the reservoir?
Foaming, cavitation, and evaporation of the fluid
What is an accumulator?
A part that stores potential energy in the form of compressed gas or spring.
What are the 4 principles of accumulators?
Bladder (gas and fluid separated by diaphragm)
Spring loaded
Weight loaded (piston compress gas against a weight)
Piston type (2 pistons pushed together by fluid and gas)
What are the main functions of a hydraulic actuator?
Store energy Absorb pulsation Cushion operation shock Maintain pressure Supplements pump delivery (back up source)
When would auxiliary pressurisation be used?
To support the mains there is a higher demand
To replace the mains in an emergency
For maintenance purposes (I.e. testing)
What are the sources for auxiliary pressure?
RAT
PTU
Electric pump
Ground source
What is a PTU?
A mechanism that transfers hydraulic pressure between systems without transfers if any fluid
How can the units in a PTU operate?
Pump or hydraulic motor
What are the parts of a filter?
Filter head
Filter bowl
Filter element
Bypass
What does a pop out indicator show?
That the filter bypass has been triggered by the differential pressure switch
The filter could be blocked
What does a manifold/module do?
Combines the major distribution components together for easier maintenance. (Filters, valves, transmitters, etc.)
What is the purpose of the priority valve?
To cut off less important users to cope with high demand situations (I.e. landing gear vs flight controls
