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B.  Case Drain Filter
(1)  A case drain filter installed in the return line, filters the fluid before it enters the standby reservoir (Fig. (2) The filter is installed to detect incipient pump or motor failures and to prevent contamination of the standby reservoir. The filter is installed in the wheel well and consists of a filter head, noncleanable filter element, a filter bowl, and a magnetic plug for checking ferrous contamination without filter disassembly (Fig. 5).
6.  Standby System Relief Valve
A.  The cartridge type standby system relief valve installed in tthe modular unit (Fig. 2) protects the system against damage by abnormally high pressures. The valve is set to relieve at 3500 (+ 50) psi and reset at 3400 psi. The valve is set by the manufacturer and no maintenance other than removal and installation is recommended.
7.  Standby System Operation
A.  The standby reservoir supplies a positive flow of fluid to the electric motor-driven pump (Fig. 2). Pump operation is controlled by either the standby rudder A, standby rudder B, or the alternate flaps switch. Refer to Chapter 27, Rudder Hydraulic Control System, and Leading Edge Flaps and Slats System. With the pump motor energized, the pumps start at full volume flow to supply fluid through a pressure filter to the hydraulic systems. As pressure increases to 1200 (+ 250) psi, the pump low pressure switch is actuated causing the low pressure light on the pilots' overhead panel to go out. As system pressure approaches 3000 psi, the pump automatically adjusts output to the need of the system. If system pressure increases to 3500 (+ 50) psi, the system pressure relief valve will open to reduce pressure to 3400 psi. At low pump demand, the pump automatically adjusts displacement and case drain flow is directed through a return filter and check valve to the reservoir.
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STANDBY SYSTEM HYDRAULIC RESERVOIR - REMOVAL/INSTALLATION
1. General
A.  The standby system reservoir is mounted on the keel beam between the left and right wheel wells (Fig. 401).
B.  A container will be necessary to catch fluid when disconnecting hydraulic lines during removal of the reservoir. Should any fluid be spilled on the airplane , the affected area must be decontaminated. Refer to Chapter 12, Cleaning and Washing.
2.  Equipment and Materials
A.  Suitable container to catch hydraulic fluid (approx 4 gal. capacity)
B.  Regulated source of nitrogen - 0 to 200 psi maximum pressure
C.  Skydrol Assembly Lube - MCS 352 or Fire Resistant Hydraulic Fluid - BMS 3-11
3.  Prepare Standby Reservoir for Removal
A.  Depressurize hydraulic reservoir system. Refer to 29-09-300, Hydraulic Reservoir
Pressurization System - MP.

B.  Tag system B and Standby pump switches to prevent operation.
C.  Open system B reservoir drain valve and drain approximately 2 gallons of hydraulic fluid into container.
NOTE: If reservoirs are completely serviced at removal of standby reservoir, approximately
1.8 gallons will drain thru the balance lines from system A reservoir.
D.  Close and secure system B reservoir drain valve with lockwire.
4.  Remove Standby Reservoir

A.  Disconnect balance line from top of standby reservoir and catch fluid drainage from balance line in container.
B.  Remove pump supply line at quick-disconnect coupling at bottom of reservoir (Fig. 401).
C.  Remove opposite end of pump supply line at standby pump.
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Standby Hydraulic Reservoir Installation  500 
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D.  With flexible pump supply line placed in container, reconnect disconnect coupling end of supply line to supply outlet fitting at bottom of reservoir and allow all fluid to drain into container.
E.  Disconnect remaining hydraulic lines from reservoir.
F.  Install protective covers over fittings and hoses.
G.  Disconnect electrical connector from low level warning switch at top of reservoir.
H.  Remove bolts attaching reservoir to mounting assembly and remove reservoir.
5.  Install Standby Reservoir

A.  Install O-rings, check valve, unions and reducers in reservoir ports. Apply hydraulic fluid or assembly lube to O-rings and to threads of check valve and all unions, reducers and couplings to facilitate installation.
　
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