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Standby System Hydraulic Reservoir
A.  A 1.9 gallon capacity hydraulic reservoir supplies hydraulic fluid to the standby hydraulic system. The reservoir is an air-tight vessel consisting of a metal shell with supply, return, balance line and fill ports. Baffles just inside the return port are provided to prevent fluid vortexing. Attached to the top of the reservoir is a low level warning switch which is connected to a low quantity warning light on the pilots' overhead panel. The reservoir is filled from the hydraulic fluid filling station. The reservoir is located on the keel beam between the left and right wheel wells.
B.  The standby system reservoir is pressurized to approximately 45 psi through a balance line connected to system A and system B reservoirs.
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Standby Hydraulic System Component Location  500 
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525  Standby Hydraulic System Schematic 
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3.  Standby System Electric Motor-Driven Hydraulic Pump
A.  One electric motor-driven hydraulic pump supplies fluid under pressure to the hydraulically-operated systems supplied by the standby system. Pump operation is controlled by either the RUDDER standby control switch, or the ALTERNATE FLAPS control switch (Ref to Chapter 27, Rudder Hydraulic Control System, and Leading Edge Flaps and Slats System).
B.  The pump assembly consists of a 3-phase 115 volt ac motor and a variable delivery, positive displacement hydraulic pump. The hydraulic pump consists of the units shown in Fig. 3. Pump pressure is regulated at 2975 to 3100 psi and maximum output is 3 gpm. Pump pressure, return and supply ports are connected to flexible hoses. The pump assembly is installed on the keel beam between the wheel wells. 28 volt dc relays control motor power. Pressure compensation inside the pump varies the ratio between the volume of fluid that is delivered to the system and the volume that is recirculated within the pump. Some fluid is discharged out the return port.
C.  The pump control (compensator) consists of a compensator cylinder, a compensator stem with a plate carrying piston sleeves, and a compensator spring unit. A small difference in the stem diameter provides an annular area on which the pressure of discharged fluid produces a force. This force is opposed by the control spring. When the discharge pressure exceeds 3000 psi, the hydraulic force on the stem overcomes the control spring and pushes the compensator stem with piston sleeves away from the driving shaft. The sleeves keep the discharge holes uncovered during nearly the whole discharge stroke, and no fluid is delivered to the pressure line. A small quantity of fluid discharged through the piston bypass holes to the return line, provides fluid circulation for cooling and lubrication of the pump during idling periods.
4.  Standby System Modular Unit
A.  The modular unit (Fig. 4) is provided to manifold hydraulic fluid to various easily replaceable cartridge type component. The modular unit consists of a 6-port housing providing attachment provisions for the cartridge type hydraulic pump pressure filter, rudder shutoff valve, leading edge flap standby shutoff valve, pressure switch, check valve, standby system pressure relief valve, and male fittings for attaching system tubing connectors. The modular unit housing has drilled passages to provide fluid flow through the unit. The modular unit is installed on the aft bulkhead of the wheel well area.
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506  Standby System Electric Motor-Driven Pump 
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Standby System Modular Unit  525 
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5.  Standby System Hydraulic Filters
A.  Pressure Filter
(1)  A cartridge type pressure filter in the pressure line from the electric motor-driven hydraulic pump filters the hydraulic fluid before it enters the hydraulic systems (Fig. 2). The pressure filter is installed in the standby system modular unit and consists of a filter bowl and a noncleanable element (Fig. 5).
　
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