Hydraulics Flashcards
What is the normal system pressure from the engine driven pumps?
3000psi
What are the 4 backup sources of hydraulic pressure?
-electrically driven hydraulic pumps (blue and yellow)
-PTU (power transfer unit)
-RAT (blue)
-a hand pump (yellow)
What is the function of the hand pump on yellow?
To open cargo doors when aircraft is unpowered on the ground.
Why are reservoirs automatically pressurised by pneumatic system?
To prevent pump cavitation.
Where is the fire shutoff valve located on green and yellow systems?
Upstream of engine driven pumps.
When will the Yellow electric pump automatically run?
Prior to engine start, when a cargo door selector is placed in open or close position.
*in this case yellow will only power:
-cargo doors.
-alternate brake system.
-engine 2 reverser blocker doors.
When will the blue electric pump automatically run?
-on ground- normal AC power and at least one engine running.
-in flight- AC power available (even if both engines shut down).
*powered by RAT in emergency.
What is the PTU and when does it activate?
Hydraulically powered motor that allows green and yellow to pressurise each other.
Automatically actives if there is a pressure differential greater than 500psi.
*note that PTU transfers pressure between systems (NOT fluid).
What is the function of an accumulator installed in each system?
To help maintain constant pressure by smoothing transient demands during normal operations.
When will the RAT deploy automatically?
-loss of AC buses 1 & 2.
*will not deploy automatically for a hydraulic system failure.
When is the PTU inhibited (pb AUTO)?
-yellow electric pump running for cargo door operation.
-during engine start, when ENG MASTER switches in opposing positions and either nosewheel steering disconnected or park brake ON.
When will Hydraulic Fire Shutoff Valves close?
With related ENG FIRE pb.
How is hydraulic pump cavitation prevented?
Reservoirs are pressurised by reduced bleed air from engine 1 HP stage or from cross bleed ducts.
What is the function of the BLUE PUMP OVRD pb?
Allows the blue pump to run prior to engine start.
When will hydraulic pressure indication change from amber to white, and pump changes LO Amber to inline green?
Indication- white above 1450 psi (system available).
Pump- in line green above 2200 psi.
