HYDRAULIC
AIRPLANE
OPERATIONS
MANUAL
2-11-05
Page
4
Code
01
JANUARY 21, 2002
MANIFOLD
The manifold provides the following functions:
-Fluid filtering (pressure and return lines).
-Overpressure relief (main and electrical pumps).
-Pressure indications (main and electrical pumps).
Fluid leaving the pump flows to the manifold, where it is filtered and
then routed to the airplane systems. Inside the manifold, a check valve
prevents the fluid from returning to the pump, while a relief valve
diverts the excess fluid to the return line. The return line is supplied by
the fluid coming from the airplane systems, fluid drained from the
pump, fluid from the relief valve, and fluid refilled by the maintenance
personnel. Under any situation the fluid is filtered and returned to the
reservoir. The manifold incorporates two pressure switches to detect
low hydraulic pressure, and a pressure transducer to indicate system
pressure. Signals from the pressure switches and pressure transducer
are sent to the MFD and EICAS displays.
PRIORITY VALVE
The hydraulic system 1 incorporates a priority valve. If the system is
powered by the electric motor-driven pump and the landing gear is
commanded to retract, the valve will provide minimum flow to the
landing gear system and give priority to the flight control services. In
this case, the landing gear will operate through the accumulator
pressure.
ACCUMULATOR
Each hydraulic system has one accumulator. The function of the
accumulator is to keep the surges of the hydraulic pumps at a
minimum, and to keep a 3000 psi pressure available for operation of
the landing gear and main door (system 1) or operation of the
emergency parking brake (system 2).
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