Copyright D.P. Browne 2011
Hydraulic System Components
The Yellow and Blue hydraulic circuits have one engine driven pump and the Green hydraulic circuit has two engine driven pumps. The Left engine drives the Green 1 Engine pump and the Blue Engine Pump, and the right engine drives the Yellow Engine Pump and the Green 2 Engine Pump.
Engine driven Pumps
Electrical pumps
Shut Off Vavlves
Reservoir
Each engine driven pump is energized when the ENG pump button on the overhead panel is selected.
Each hydraulic circuit has one electrical powered pump. These electrical pumps do not come on automatically if the engine driven pump fails and they are not designed to take over from the engine driven pumps. The electrical pumps are used to move the control surfaces for flaps, slats etc in the event of engine driven pump failure. Therefore the electrical pumps only run for a short while.
The Blue System electrical pump runs only when manually selected
The Green System electrical pump runs when the there is a dual engine failure and the landing gear is retracted.
The Yellow System electrical pump runs when the the green electrical pump is not running to help with retracting surfaces etc following and engine failure. The Yellow electrical pump also runs automatically to open and close the cargo door on the ground.
The Fire system shut off valves also shut off the hydraulic system. For the Green System, the SOV may be closed automatically in case of a leak. The Yellow and blue system can only have a manual application of the SOV via the fire button
Each hydraulic system has a reservoir. The reservoir is pressurized by bleed air from the engines.
HMSU
The Hydraulic Monitor Sensor Unit (HMSU) monitors the 3 hydraulics systems and passes information to the EFIS for display to the flight crew,
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