HYDRAULIC
AIRPLANE
OPERATIONS
MANUAL
2-11-05
Page
2
Code
01
JANUARY 21, 2002
SYSTEM DESCRIPTION
Each hydraulic system consists of a hydraulic fluid reservoir, a
manifold, one engine-driven pump, one electric motor-driven pump,
one shutoff valve, one accumulator and a priority valve installed in the
hydraulic system 1.
RESERVOIR
The hydraulic fluid stored in the reservoir is pressurized, to avoid pump
cavitation. This pressurization function is performed by fluid drained
from the pressure line. The reservoir is equipped with a quantity
indicator which transmits information to the MFD and EICAS displays
for indication and warning purposes. A thermal switch is responsible
for the high temperature message, if the fluid temperature increases
above 90°C.
SHUTOFF VALVE
A shutoff valve is installed between the reservoir and the engine-driven
pump. It cuts the hydraulic fluid supply to the engine-driven pump, if
there is a fire on the related engine or in case of hydraulic fluid
overheat. This valve may be closed either through the engine fire
extinguishing handle or through a dedicated button on the overhead
panel.
ENGINE-DRIVEN PUMP
The engine-driven pump provides continuous fluid flow at 3000 psi for
operation of the various airplane hydraulically-powered systems. The
pump is connected to the engine accessory gearbox and, as long as
engine is running, it generates hydraulic pressure. During engine start,
the fluid remaining in the suction line is sufficient to avoid pump
cavitation and provide reservoir pressurization.
ELECTRIC MOTOR-DRIVEN PUMP
The electric motor-driven pump has the same connections as the
engine-driven pump, but has a lower flow capacity. The pump normally
operates in the automatic setting mode, turning on when the
associated hydraulic pressure drops below 1600 psi or the associated
engine N2 drops below 56.4%.
If the pump starts operating in the automatic mode, it will be turned off
after the pressure or N2 are reestablished to normal values. The
electric pump may be turned on at pilot command, through the selector
knob on the overhead panel, furnishing continuous fluid flow at 2900
psi.
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