Hydraulics Flashcards
How many Hydraulic systems are installed on the aircraft?
- 3 independent systems (HYD1 | HYD 2 | HYD 3)
What systems use hydraulic power?
- Flight controls, Spoilers, Landing gear, Nose wheel steering, Wheel brakes,
thrust reversers
Can hydraulic fluid be transferred between each system?
- NO
How many Hydraulic Pumps are on the aircraft?
- 6 total
- 2 EDP’s (Engine Driven Pumps)
- 4 ACMP’s (AC Motor Pumps)
What is the purpose of the Accumulator?
- Helps to maintain constant pressure by covering transient demands
- Helps to avoid pump cavitation
- Provides a backup source of hydraulic energy or pressure
When will ACMP 1 or 2 automatically activate with both Engines running?
- Ground
i) Flaps > 0
ii) TL set to T/O
iii) Wheelspeed > 50 kts - Flight
i) Engine failure or EDP failure
ii) Flaps > 0
What are some important items controlled by HYD 2 system?
- Landing Gear, Nosewheel Steering, Inboard Brakes
What is the PTU?
- Power Transfer Unit
- Mechanical pump that uses HYD 1 power to mechanically provide HYD 2
pressure
What is the primary purpose of the PTU?
- To allow landing gear retraction and extension in the event of an engine 2 or
EDP 2 failure
When will the PTU automatically activate?
- During takeoff and landing if the engine 2 or EDP 2 fails.
- The PTU will be started if:
i) Flaps not set to zero or LG not up and locked;
ii) EDP 1 not failed;
iii) Hydraulic reservoir 2 quantity above 12%
How is S.E. Taxi possible on ENG1 if Nosewheel Steering is on HYD 2?
- ACMP 2 will activate if engine 1 is running and the parking brake is released.
- Parking brake set after taxi, pump continues running for 6 minutes.
What is the primary purpose of HYD 3 system?
- Back-up for the flight controls.
HYD ACMP 3A & B pump switch(s) are labeled ON & AUTO because?
- HYD ACMP 3A pump is primary and has no automation
- HYD ACMP 3B pump is a back-up and automatically activates if ACMP 3A fails
What, if any, HYD ACMP will function if the RAT is the only power source?
- HYD ACMP 3A only
In an electrical emergency what provides hydraulic pressure to flight controls until
the RAT comes online?
- HYD 3 accumulator
- After 8 seconds the RAT will power ACMP 3A
In an electrical emergency can HYD 3 system power requirements overload the
RAT?
- No. Because, a flow limiter valve is used to reduce flow and limits pump electrical
power draw to prevent a RAT stall.
What is the hydraulic pressure during normal operation of the EDP(s)?
- 3000 psi
Which hydraulic pump cannot be deferred? Why?
- Hydraulic Pump 3a
- Only one powered by AC ESS BUS during electrical emergency
What does the hydraulic shutoff button do when pressed on the overhead panel?
- Closes the Shutoff Valve. Isolates fluid from the Pump but does not shut it down.
What overheat protection is provided for the hydraulic system?
- 100°C generates a High Temperature EICAS Caution message.
- 125°C shutoff valve will automatically actuate.
- 145°C generates a Hydraulic Overheat EICAS Warning message
