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bus through the AUX HYD PRESS circuit breaker. It then provides a
variable output signal, proportional to fluid pressure, to the Data Acquisition
Unit (DAU). The DAU, in turn, prompts these signals for display on the
Engine Instruments display, ENGINE START system page and
HYDRAULICS system page.
E. System Filters:
The Auxiliary hydraulic system main and return filters are bypass type
filters in that a relief valve is incorporated. If either filter element begins to
clog, the pressure differential between the filter inlet and outlet opens a
relief valve, allowing the fluid to bypass the filter element. Both filters also
include a check valve that prevents back pressure from reaching the Aux
pump discharge port.
Differential Pressure Indicators (DPIs) for each filter provide a visual
means of noting filter bypass by causing a red indicator on the DPI to “pop
up” when the pressure differential between the filter inlet and outlet
exceeds a preset value. The DPI indicator may be reset for monitoring or
troubleshooting as required.
F. Relief Valve:
The Auxiliary hydraulic system contains a pressure relief valve to prevent
system overpressurization. The relief valve is installed in the left main
wheel well. If system pressure exceeds 3850 psi, the relief valve opens to
route system pressure back to the Combined system reservoir Auxiliary
chamber. When system pressure falls to 3500 psi, the valve closes.
3. Controls and Indications:
A. System Control:
(1) AUX PUMP OFF/ARM and ON/OFF Switches (Figure 18):
OPERATING MANUAL
2A-29-00 PRODUCTION AIRCRAFT SYSTEMS
Page 26
October 11/02
Revision 8
The Aux pump is normally operated with the AUX PUMP ON/OFF
switch located in the HYDRAULIC CONTROL section of the cockpit
overhead panel. Selection to ON starts the pump, deslection stops
the pump.
The AUX PUMP OFF/ARM switch provides a means of
automatically starting the Aux pump. With the OFF/ARM switch
selected to ARM, the Aux pump will start automatically if:
• Either nutcracker is in the GROUND mode
• Combined and Utility hydraulic system pressures are less
than 1500 psi
• Any toe brake pedal is depressed more than 10°
With the OFF/ARM switch selected to OFF, automatic operation is
inhibited.
(2) DOOR Switch Controls (Figure 13 and Figure 14):
As stated previously, the Aux pump is the only source of hydraulic
power for closing the main entrance door. Provided the DOOR
SAFETY SWITCH is not selected to SAFE, the Aux pump will start
automatically when either the INSIDE DOOR CONT SWITCH
(pilot’s circuit breaker panel) or OUTSIDE DOOR SWITCH (forward
left fuselage) are selected to CLOSE. It will continue running until
the door is closed and locked, when it will shut off automatically and
return the appropriate DOOR switch to neutral.
(3) Ground Service Valve Controls (Figure 15):
A ground service valve is located inside an access door just aft of
the right nose landing gear door. With power applied to the Essential
28V DC bus, movement of the spring-loaded valve handle permits
fluid flow to the landing gear and landing gear doors. At the same
time, the moving handle contacts an Aux pump control switch,
activating the Aux pump. Releasing the handle stops the Aux pump
and returns the valve to its normal position.
(4) Cargo Door Switch Controls:
On aircraft with ASC 213 or ASC 354 incorporated, the Auxiliary
hydraulic system also serves as the only source of hydraulic power
for opening and closing the cargo door. Unlike main entrance door
operation, however, cargo door operation requires that the Aux
pump be manually selected on and off using the cockpit switches
when opening and closing the cargo door using its OPEN/CLOSE
switch. For a detailed description of the cargo door, see Section
2A-52-00, Doors.
B. Auxiliary Hydraulic Pump Controls – Preflight Check:
During preflight, automatic operation of the Aux pump should be tested as
follows:
(1) Verify that both Combined and Utility hydraulic system pressures
are below 1500 psi.
(2) Select the AUX PUMP OFF/ARM switch to ARM (NOT ARM switch
legend extinguished).
(3) Depress any brake pedal.
OPERATING MANUAL
PRODUCTION AIRCRAFT SYSTEMS 2A-29-00
Page 27
October 11/02
Revision 8
(4) Verify the Aux pump starts and remains on after releasing the brake
pedal.
(5) Select the AUX PUMP OFF/ARM switch to OFF (NOT ARM switch
legend illuminated).
C. Circuit Breakers:
The Auxiliary hydraulic system is protected by the following circuit breakers
(CBs):
Circuit Breaker Name: CB Panel: Location: Power Source:
　
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