Hydraulic System Flashcards
Hydraulic System
3 systems
Use skydrol
Operate at 3000psi
Main Components are
2 Engine driven pumps
4 AC pumps
1 PTU hydraulic power transfer unit
3 hydraulic reservoirs
Systems 1&2
Powered by 1 Engine driven pump each
Backed up by 1 AC pump each
Usage of the electric pumps
Electric Hydraulic pumps are used during Take off & Landing and in the event of engine or engine driven pump failure.
PTU is installed between the 2 systems to transfer Hydraulic power from System 1 to 2 without mixing fluid between the systems.It is used for landing gear retraction and extension if the engine driven pump at System 2 fails
PTU WILL NOT OPERATE IF airspeed <50kts and when on the ground
Electric pumps are used in TO & Landing to avoid any disturbances if an engine driven pump or an Engine failure occurs. They are activate when :
Flaps extended
Groundspeed >50kts
Thrust Levers to Take Off
And minimizing the effect of switching to the back up pump.
System 3 will not be affected by the loss of an engin power.
System 3 operation
By
1 main hydraulic pump
1 auxiliary electric hydraulic pump as a back up
The system philosophy
It is designed so even the in case of 2 systems failure the 3rd to be operational for the flight critical functions.
System 1 operates
Left Outboard Elevator PCU
Rudder Upper PCU
Engine 1 Reverser PCU
MF spoiler 3/4
GND Spoiler 2
Brake Outboard
Emergency Parking Brake
System 2 powers
Left & Right Elevator PCUs
Left & Right Aileron inboard PCU
Engine 2 Reverser
MF Spoiler 5
GND Spoiler 1
Brake Inboard
Nose Wheel STR
Emergency Parking Brake
Landing Gear
System 3 powers
Right Elevator outboard PCU
Rudder Lower PCUs
Left & Right Outboard PCU
How to control
From the flight deck
4 rotary knobs for the AC pumps
1 rotary knob for the PTU
2 Guarded buttons for the firewall shutoff valves
AC pump knob positions
When in AUTO 1,2 they turn On automatically during TO and Landing or when primary pump pressure is lost.
Pump 3B activates automatically when 3A fails and is not activated during TO & Landing.
PTU
In case end2 or edp2 fails, the PTU is activated automatically when in AUTO position and NOT Flaps0
The ON selection
We can turn it to ON in case the SPDA goes Offline
Overheat condition can be caused by
A pump compensator failure -> rapid rise of hydraulic fluids temperature
System 3A&3B switches off automatically when temp. reaches 125celsius
What is an SPDA
Secondary Power Distribution Assembly
What happens if RAT deploys
The SPDA2 commands the PUV (pump unloaded valve) to open and reduces the fluid flow through AC pump 3A during pump startup and the FLV (flow limiter valve) is energized and reduced the flow to 1.75-2 gallons/min and spin the turbine faster that it’s operational speed.
Then the turbine produces power to the AC essential bus AC and when the AC pump 3A starts it will command the PUV to close and increase the system pressure to normal. FLV will remain ON while the ram air or the rap air turbine generator produces power.
In case of 2 engines loss either simultaneously or one at a time, what happens with the controls?
In the beginning the AC pump 3A will turn off due to electrical power loss when the IDGs go offline but the System Accumulator will provide necessary power to the flight controls to the system 3 while the Ram Air Turbine deploys then speeds up its operating speed and starts the AC pump 3A.
What is an IDG
Integrated Drive Generator: the main source of A.C (alternating current) electrical power on the aircraft.it is a combination of a constant speed drive (CSD) and an electrical generator driven by the engine through the accessory gearbox
What about Engine 1 taxi?
When engine 1 starts and parking brake is released the AC pump 2 is activated to operate the Nose Gear Steering and the inboard brakes.
EICAS message
“HYD 1 HI TEMP” amber
“HYD 1 OVERHEAT” red
Amber : Appears when fluid reaches 100°C and at 125°C the SOV actuates isolating EDP1
Red : Overheat at 145°C, SOV manually can be commanded through the guarded push button
Engine Flameout
FADEC automatically commands the respective EDP to unload and depressurising the system to perform a windmill restart
PTU
Consists of a Hydraulic pump in System 2 driven by a hyd motor in Ststem 1. Should the right engine or EDP fails it assists in the retraction/extension of the landing gear.
EICAS “HYD PTU FAIL” amber
When PTU malfunction is detected. Follow applicable abnormal procedures
PTU set to AUTO
During TO & Landing the PTU will be automatically started if all met:
- Flaps/Slats NOT “0”
- Landing gear NOT up and locked
- EDP 1 NOT Fail
- Hydraulic reservoir 2 quantity above 12%
DUMP button pressed once
Cabin depressurisation (opens outflow valves to close the packs & recirculation fans.
A white stripe appears on the button
To return to normal, push it out
BUT If when pressed the aircraft is at 12400ft< then to expedite the rate of climb use the MAN MODE (Selector knob) otherwise the rising will be due to a normal leak
Auto operation of CPCS
- Sets the ECS packs& recirculation fans to OFF
- Controls the OUTFLOW VALVE to maintain cabin altitude rate of climb 2000ft/min up to 12400ft
-After 12400ft OUTFLOW VALVE closes and then rises by natural leak.
