11.11 hyd power Flashcards
what psi does civil aircraft hydraulic systems work at
3000 psi
what are the 2 types of hydraulic pressure
hydrostatic, hydrodynamic
what is hydraulic fluid stored in
a reservoir
to have enough redundancy for safe flight what happens with hydraulic systems
have multiple systems of the same design
how are the 3 hydraulic systems identified
blue, green, yellow
aircraft with two or more hydraulic systems are required to have what
independent mechanical system
what is an open-centre hydraulic system
one fluid flow but no system pressure when mechanisms are idle
what is a closed-centre hydraulic system
fluid is un der pressure whenever power pump is operating
in a closed-centre hydraulic system if constant delivery pumps are used what is also required
pressure regulator, relief valve
whats an advantage of the open centre system over the closed centre system
continuous pressurisation of the system is eliminated
what is a hydraulic power pack system
compact unit with a pump, reservoir, valves, filters, pressure relief valves
whats the advantage of a power pack
no need for centralised hydraulic power supply system or long hydraulic lines
what oil properties do modern aircraft require
low flammability, corrosion resistant, good lubrication, non-evaporating, chemical stable
if a fluid is hygroscopic what does it tend to do
absorb water
whats one of the most important properties of hydraulic fluid
viscosity
what is viscosity
internal resistance to flow
whats viscosities relation with temperature
viscosity increases as temp decreases
what is chemical stability
liquids ability to resist oxidation and deterioration for long periods
are liquids with higher viscosity more or less resistant to temp
more resistance
what is flash point
temp at which a liquid gives off vapour sufficiently to ignite
what is fire point
temp at which a substance gives off vapour in sufficient to ignite and continue to burn
what are the 3 principal categories of hydraulic fluids
minerals, polyalphaolefins, phosphate esters
when are mineral based fluids usually used
when fire hazards are low
can mineral oil be mixed together and what colour are they dyed
can be mixed and are dyed red
whats the disadvantage of polyalphaolefin based fluids
high viscosity at low temperatures
what is the most used hydraulic fluid
phosphate ester based fluid (skydrol)
what are the 2 classes of type IV fluids
class I are low density, class II are standard density
what are the 2 general hydraulic fluid contaminants
abrasives, non-abrasives
what is used for contamination control
filters
if a hydraulic system is found contaminated what must happen
system flushed
what are the 2 main servicing activities for the hydraulic system
reservoir filling, fluid sampling
where does pressurised filling take place
service panel
what do you use for manual filling of the reservoir
hand pump
where is the hydraulic fluid sampling valve located
high pressure manifold of each hydraulic system
what type of valve is the hydraulic sampling valve
needly type valve
where is the hydraulic fluid sampled on boeing aircrfat
low pressure part of system
how often does a hydraulic system need to be sampled
once a year or every 3000 flight hours
is synthetic oil toxic to humans
yes
what is the function of the reservoir
store fluid for the system
where is the first place a fluid goes after leaving the reservoir
pump
what can a reservoir also serve as in a fluid system
overflow basin
what are reservoirs classified as
pressurised, non-pressurised
where are mesh filters located in the reservoir
filler neck
what aircraft are non-pressurised reservoirs used in
aircraft that dont perform violent manoeuvres or at high altitude
what aircraft are pressurised reservoirs used on
aircraft that fly at high altitude
whats the function of the reservoir pressurisation module
provide bleed air into the reservoir for pressurisation
some aircrafts reservoirs arent bleed air pressurised, what else can pressurise them
hydraulic system pressure
how are non-pressurised reservoirs service
pouring hydraulic fluid directly into the filler strainer
what is a hydraulic accumulator
device where potential energy is stored
what are the 2 types of accumulators used in hydraulic systems
spherical, cylindrical
what happens during the pre-load of the accumulator
compressed nitrogen in charged to just below system operating pressure
what must be done before checking an accumulators pressure
hydraulic system must be unpressurised
how many power driven pumps do aircrafts hydraulic systems have
at least one
whats the function of the power driven pump
drives fluid in the system
what are pumps in the hydraulic system classified as
positive displacement, non-positive displacement
what classification of pump are mainly used in hydraulic systems
positive displacement
what do constant displacement pumps do
deliver fixed quantities of fluid regardless of pressure
is a gear type power pump positive or negative displacement
positive
is a gerotor pump positive or negative displacement
positive
whats good about piston pumps
can be variable or constant displacement
what is a typical constant displacement axial type pump
bent axis piston pump
what the simplest axial piston pump
inline piston pump
what is displacement determined by in inline piston pumps
size of the piston
what is a VDP
variable displacement pump
what does a variable displacement pump convert
mechanical energy to hydraulic energy
what generates hydraulic system pressure
power driven pump
what is an EDP
engine driven pump
what is the engine driven pump
variable displacement pump permanently connected to the engine
whats an ACMP
alternating current motor pump
whats an ADP
air driven pump
what type of pump is an air driven pump
variable displacement pump
what are the 3 types of hand pump
single action, double action, rotary
what are 3 uses for emergency and backup pressurisation
maintain pressurisation, replace main pressurisation, maintenance purposes
what is emergency and backup pressurisation produced by
RAT
what is RAT
ram air turbine
how long does RAT deployment take
less than 1 second
whats a PTU
power transfer unit
what can electrically driven hydraulic pumps also be used as
primary source of pressurising the hydraulic system in an emergency
what is the cause of over 85% of system failure
contamination
what materials can hydraulic filters come in
wire mesh, stainless steel, micro glass, cellulose paper
what are wire mesh filters made from
steel
what hydraulic filter provides best filtration quality
micro glass
what sized of contamination can micro glass filters stop
10 microns or greater
whats the function of the filter bypass valve
opens if the filter gets clogged
what happens when a filter element needs cleaning
a red popout will appear
whats the purpose of a relief valve
open when pressure exceeds a certain level
what are the most common types of relief valve
ball type, sleeve type, poppet type
whats the purpose of pressure regulators
regulate the required pressure under different conditions
what do pressure reducers do and where are they used
when a lower pressure is required than the supply system it slowly decreases its pressure
whats the function of seals
prevent fluid going pasta certain point
what 3 classes are seals divided into
packing, gaskets, wipers
what types of packing seal are there
v-rings, u-rings, o-rings
what are the colours of o-rings and their compatibility
red- fuel
blue - hydraulic fluid
in areas with high differential pressure what other seal may be used
backup seal
when are static seals used
seal against steady or pulsating pressure
when are dynamic seals used
stroking or rotational movement occurs
what material is used when a heat resistant gasket is required
asbestos
what should you avoid using when installing/removing seals
sharp tools
what are the types of non-return valves
check valves, clack valves, reflux valves, retention valves, one way valves
whats the function of a shuttle valve
isolate the normal system from the emergency system
what are hydraulic fuses
safety devices that can shut off flow in conditions
what are heat exchangers used for in the hydraulic system
cool hydraulic fluid from the pumps before it returns to the reservoir
pipe fitting come in 2 types, what are they
disconnecting, non-disconnecting
what are non-disconnecting pipe fittings used for
to repair broken pipes
what classification can hoses be separated into
low, medium, high
are hose fittings non-disconnecting or disconnecting type
disconnecting type
what are the primary parameters measured of the hydraulic system in the cockpit
fluid pressure, temperature
whats located in the hydraulic system to display parameters in the cockpit
electrohydraulic tranducers
what is hydraulic fluid quantity measured using
a float in the reservoir
pressure sensors can be divided into what subsets
pressure switches, pressure transducers
for maintenance what are usually attached to the accumulators and are they calibrated
pressure gauge, not calibrated
what are HMDGS
hydraulic motor driven generators
in the case of electrical failure what is deployed
hydraulic motor driven generator (HMDGS)
