11.11 Flashcards
How much psi in large transports
5000psi
Civil aircraft pressure figure
207 bar or 3000 psi
How do we create a higher force
Increase diameter of actuator or pressure
What are the 2 types of hydraulic pressure
Hydrostatic pressure
Hydrodynamic pressure
How do you make sure there is enough redundancy for safe flight
Several hydraulic systems
Aircraft with two or more hydraulic systems are required to have what
Independent mechanical system
Airbus pressure distribution section
Manifold
Boeing pressure distribution section
Module
An open centre system has fluid flow but what does it not have
No pressure in system when actuating mechanisms are idle
When is the fluid under pressure in a closed centre system
Whenever the pump is operating
Advantage of open centre vs closed centre
Continuous pressurisation of system is eliminated
Why are small power packs good
Reduces weight by eliminating hydraulic lines and large quantities of hydraulic fluid
What pressurises quicker and transmits force more efficiently , fluid or gas?
Fluid
What is chemical stability
Ability to resist oxidation and deterioration for prolonged periods
What flash point do we want
High for good resistance to combustion and Low degree of evaporation at normal temperatures
What fire point do we want
High
Diffrenve between flash point and fire
Fire point is when it will continuously burn
When would mineral oil be used and is it interchangeable?
When fire hazard is low & it is interchangeable and dyed red
What is a problem with polyalphaolefin based oil
High viscosity at low temperatures
Most common aircraft hydraulic fluid
Skydrol
What the advantage to type IV type 1 have
Weight saving
What fluids don’t mix
Petroleum and phosphate ester
Where does pressurised filling happen
Service panel
Where is the sampling valve
Hp manifold
What’s the sampling valve end cap
Products valve from dirt and also tool to open needle valve (sampling valve)
How often is a routine sample for hydraulic sampling
Once a year
every 3000 flight hours
when airframe manufacturer suggests
What should you do if u suspect contamination
Fluids drained and replaced and samples taken
Where is leak measurement manifold linked to
Hp manifold
What aircraft uses non pressurised resouvoris
Aircraft that is non designed for violent manouvers
Fly at high altitudes
Or where resouvoir is in a pressurised area
What’s the purpose of the reservoir pressurisation module
Supplies bleed air to the reservoirs
How many filters and check valves does a pressurisation module have
2
What does an accumulator do
Accumulate energy and smoothen out pulsations
What is a spherical accumulator and what does it contain
Steel sphere divided into 2 chambers
Top is fluid at system pressure
Bottom is charged with nitrogen or air
What is a cylindrical accumulator
Piston separates fluid from air
How is a piston sealed in a cylindrical accumulator
Double seal rings to prevent internal leakage
Where are cylindrical accumulators used
High pressure systems
What is an accumulator preload
Nitrogen chamber charged to pre determined pressure lower then system operating temperature
What’s the primary source of pressure generation
Mechanical driven pumps
What’s a non positive displacement pump
Produces continuous flow but output varies with pressure
What’s a constant displacement pump
Forces a fixed amount of fluid with each revolution
What kind of pump is a gerotor
Positive displacement
What type of pump is a piston pump
Constant displacement or variable
Most common main system (positive displacement)
What is a drive coupling
Short shaft with set of male splines on both ends
What kind of device is a pump drive coupling
Saftey device
What type of pump is axis piston
Constant displacement axial pump
What type of pump is a vane pump & many blades in a vane pump
Constant displacement pump with 4 blades
What does a variable displacement pump convert
Mechanical energy to hydraulic and vice versa
What pump is more energy efficient
Variable displacement is more efficient then fixed
What term is used to describe primary hydraulic power
Main pressurisation
When are electrically driven pumps used
Emergencies and during ground operation when engines aren’t running
Why are hand pumps installed
Testing and emergencies
Why is single action hand pump not used
Inefficient
What type of pump is the RAT
Vdp
How is the electric motor of the pump cooled
With air or hydraulic fluid
What percentage of system failure is down to contamination
85%
How many microns in an inch
25400 microns
What filter is used for surface cleaning
Wire mesh
Which filter has the best filtration quality
Micro glass as it stops anything bigger then 10 microns
What does a bypass relief valve do
Opens if the filter clogs as dirty oil is preferred over no flow
What is the purpose of a filter bypass system?
The filter bypass system is activated when the filter element becomes clogged and unable to filter, allowing unfiltered fluid to bypass the filter element.
Example sentence: A spring-loaded valve opens to allow the unfiltered fluid to bypass the filter element.
What is a differential pressure indicator used for?
A differential pressure indicator is used to provide a visual sign that the filter is clogged and the filter bypass has been activated.
Example sentence: A red button installed on the filter pops into view when the filter is clogged, and it stays in view even if the bypass valve opens.
What are the configurations of differential pressure indicating devices?
electrical switches, continuous reading visual indicators, and visual indicators with memory.
Example sentence: Visual indicators with memory usually take the form of magnetic or mechanically latched buttons or pins that extend when the differential pressure exceeds that allowed for a serviceable element.
Why are visual indicators with memory useful?
Visual indicators with memory provide a permanent warning of a loaded element, particularly in remote locations where continuous monitoring is impossible.
Example sentence: The button or pin, once extended, remains in that position until manually reset, providing a permanent warning of a loaded element.
What does a pressure relief valve consist of
Spring loaded valve which is operated by hydraulic pressure and spring tension
3 most common pressure relief valves
Ball
Sleeve
Poppet
What does a thermal relief valve do
Relieve pressure due to thermal expansion
Purpose of pressure regulator
Manage output to pump to maintain system operating pressure within a predetermined range
Pump to turn without resistance
What seals are used on moving parts
Packing’s
What seals are used on non moving parts
Gaskets
What are v rings
One way seal and it faces the pressure
What are u ring seals used for
Brake assemblies and pressure under 1000psi
What direction does a u ring seal
One direction
What direction is an o ring
Both
What’s a red oring for
Fuel
What colour is a hydraulic fluid o ring
Blue
Backup ring material
Teflon
What to check in a back up ring
Coils don’t separate more then 1/4 inch when unrestrained
When are static seals used
Steady or pulsating force
When is a dynamic deal used
Stroking or rotational movement
What do we sue a asbestos gasket
Heat resistance
When do we use a copper gasket
Non compressive semi soft gasket , spark plug
When do we use cork gaskets
Oil seal between engine crankcase and accessories
When do we use a rubber gasket
When a compressible gasket is needed
Before you install an oring what should you do
Immerse it in clean hydraulic fluid
What are the 3 common valves
Ball , sleeve , poppet
What do flow control valves do
Control speed and direction of fluid in hydraulic system
What are the two selector valves and what do they do
Open - continuous flow even when selector can’t actuate a unit
Closed - blocks flow where valve is in neutral or off position ( 4 port valves most used)
What the purpose of a quick disconnect valve
Prevent loss of fluid when unit is removed
What does a shuttle valve do
Isolate normal system from an alternate or emergency system
What a heat exchanger used for
Cool hydraulic fluid
How do we ensure there is a leak proof joint on a disconnecting pipe fitting
Locate the sleeve on the pipe in the right position
What’s a non disconnecting pipe fitting used for
Repair broken pipes by swaging
Hose classification
Low
Medium
High
( always disconnecting type)
What’s case drain fluid used for
Cool and lubricate pump before entering reservoir
How is a subsystem indicated
Particular number and colour
What does a pressure transducer do
Convert one form of energy to another
What’s a bourdon tube
Elastic type pressure transducer
Used for liquid and pneumatic pressure measurements
Range of 100,000 psi
How do you overcome the short comings of fly by wire
Use power by wire
How do you overcome the short comings of fly by wire
Use power by wire
When is a hydraulic motor driven generator used
When electrical failure occurs as it’s an alternative source of power
It’s an AC generator
