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A visual sight gauge on the aft end of each reservoir piston provides
an indication of reservoir fluid quantity by denoting the FULL and
REFILL fluid levels. No electrical power is necessary to use the
visual sight gauge, but the system must pressurized to 3000 psi to
obtain an accurate reading. The proper fluid level for the reservoir is
the FULL indication on the sight gauge.
(8) Reservoir Vacuum Relief Check Valve (Combined System Only):
The Combined system’s reservoir vacuum relief valve opens at a set
negative pressure to allow ambient air into the reservoir. This
prevents auxiliary hydraulic pump cavitation.
(9) Reservoir Piston Scuppers:
A piston scupper is installed on each reservoir to catch any fluid
leakage from the reservoir piston end. This leakage is then vented
overboard.
B. System Shutoff Valves:
System shutoff valves (Figure 6) are installed in the tail compartment to
control fluid flow from each reservoir to its respective engine-driven
hydraulic pump. They are normally open, electrically operated, motordriven,
gate-type valves.
Pulling the associated FIRE handle supplies 28V DC from the Essential DC
bus to the valve motor. The motor then drives the valve closed. Pushing in
the associated FIRE handle opens the valve.
Valve position signals are supplied to the Fault Warning Computer (FWC)
for use on the Engine Instruments display, ENGINE START system page
OPERATING MANUAL
PRODUCTION AIRCRAFT SYSTEMS 2A-29-00
Page 7
October 11/02
Revision 8
and HYDRAULICS system page. When the valve is in transit, amber
dashes are shown in the associated system pressure display window.
When the valve is closed, amber crosshatching is shown in the window.
Valve position is also shown on the valve itself by a red pointer flag/lever
pointing to either OPEN or CLOSED. The flag/lever may be manually
moved to the desired position. However, if the valve is moved to the
CLOSED position, the associated HYD S/O circuit breaker must also be
pulled to prevent the valve from being driven to its normally open position
when power is applied to the aircraft.
C. Manually Operated Shutoff Valves:
A manually operated shutoff valve controls hydraulic fluid flow from the
Combined and Flight hydraulic systems to the flight control actuators.
Pulling the FLIGHT POWER SHUT OFF handle on the cockpit center
pedestal (Figure 7) closes the shutoff valve through the use of a controlex
cable. For detailed information on this system, see Section 2A-27-00: Flight
Controls.
D. Engine Driven Hydraulic Pumps:
A positive displacement, constant delivery hydraulic pump is installed on
each engine’s right-hand high pressure gearbox (Combined on left engine,
Flight on right engine). The pumps draw fluid from their respective reservoir
and deliver the fluid under pressure to the using systems.
A small quantity of hydraulic fluid lubricates and cools the pump. This fluid
is then returned to the reservoir through the bypass port.
During normal operations, fluid flows through the heat exchanger and
engine pump bypass to the reservoir. At low ambient temperatures, when
fluid is viscous, a relief valve opens at 100 psi to route engine pump bypass
flow through the main return filter to the reservoir.
E. Hydraulic Heat Exchangers:
Combined and Flight hydraulic system fluid is circulated though dedicated
hydraulic heat exchangers installed in the wing fuel hoppers (Combined in
left hopper, Flight in right hopper). Functioning as a radiator, each heat
exchanger allows the warmer hydraulic fluid to dissipate heat into the
surrounding cooler fuel. This has an added benefit in that raising the fuel
temperature within the hopper helps to alleviate cold-soak conditions.
F. Check Valves, Snubbers and Pressure Transmitters:
Pressurized fluid from each system’s engine driven pump passes through a
check valve installed to prevent reverse flow to the pump. A snubber
installed downstream of the check valve at the pressure transmitter’s inlet
port damps any pressure surges in order to prevent erratic pressure
indications.
Each system’s pressure transmitter receives 28V DC power from the
Essential DC bus. It then provides a variable output signal, proportional to
fluid pressure, to the respective DAU. The DAU in turn prompts these
signals for display on the Engine Instruments display, ENGINE START
system page and HYDRAULICS system page.
G. Pressure Switches:
Each hydraulic system has a pressure switch installed downstream of the
pressure transmitter to monitor system pressure.
OPERATING MANUAL
2A-29-00 PRODUCTION AIRCRAFT SYSTEMS
　
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