(2)
When the parking brake is set and the parking brake relay is energized, power is available to operate the ground interconnect valve. Positioning the ground interconnect valve switch to OPEN allows system A to be pressurized by system B. Also, the switch must be placed in the OPEN position when pressurizing system A with an external source connected to the ground power module. A check valve is installed to prevent system B from being pressurized by system A. The interconnect valve is always closed when the parking brake is off and electrical power is applied to the airplane.
500
Nov 15/68 29-11-0
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. Page 17
HYDRAULIC SYSTEM A - TROUBLE SHOOTING
1. General
A. Hydraulic systems A and B will be checked separately except when checking for external leakage. When checking for leakage, pressurize both systems A and B and examine all components, hydraulic fittings and connecting lines. Pin hole leaks may be detected by noting damp spots on the airplane and tracing run back fluid to locate source of leak. When disconnecting hydraulic lines during removal of components, take care to prevent spillage of hydraulic fluid. Should fluid leak on the airplane or spill while performing maintenance, the affected area must be decontaminated in accordance with instructions in Chapter 12, Cleaning and Washing.
B. Illumination of either the No. 1 or 2 engine-driven pump low pressure warning lights during operation of system A and a confirmation of loss of pressure on the affected pump should be followed by a check of the corresponding pump pressure filter and case drain return filter. Contaminated filter elements indicate a defective pump. A pump need not be operated again following warning light illumination unless filter check shows no sign of contamination and trouble is suspected outside the pump. If additional information is required on the pump low pressure warning lights, refer to 29-34-0, Hydraulic Pump Low Pressure Warning Systems.
C. When trouble shooting the hydraulic system, system A should stabilize between 2800 and 3100 psi with flight control switches ON and ground interconnect valve CLOSED and 2900 to 3100 with flight control switches OFF and ground interconnect valve CLOSED.
D. If either engine No. 1 or 2 fire switches are positioned to FIRE with the corresponding engine-driven pump operating, proceed with the following steps:
(1)
If a supply shutoff valve was closed for less than 5 minutes, no maintenance is required and shutoff periods are not accumulative.
(2)
If supply shutoff valve was closed for longer than 5 minutes:
506
Feb 20/89 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 29-11-0 Page 101
NOTE: Ensure that pump has operated at least one minute with supply fluid available before checking filter elements/bowl so that metal contamination, possibly generated during fluid shutoff, has reached the filter.
(a)
Check case drain filter element for metal contamination (Ref\29-11-41, Serv)
(b)
Check pressure filter for metal contamination (Ref 29-11-71, Serv)
(c)
If no metal is found in either filter, install new filters and continue to run pump (Ref 29-11-41 R/I and 29-11-71 R/I). Recheck filters in 200 hrs.
(d)
If metal is found, remove applicable pump for overhaul & flush lines between the pump and filters (Ref MP).
2. Prepare System A Hydraulic System for Trouble Shooting
A. Service hydraulic reservoir system (Ref Chapter 12, Hydraulic Servicing).
B. Pressurize hydraulic reservoir system (Ref 29-09-300 MP).
C. Connect electric power to airplane.
D. Check that parking brake is set.
E. When trouble shooting engine-driven pumps, pressurize system by motoring engines (Ref 71-09-100, Operating Procedures).
F. If pressurizing system A using system B pump, refer 29-11-0, Hydraulic System A - MP.
3. Hydraulic System A Trouble Shooting Chart
NOTE: Hydraulic pump high and low pressure adjustments are made on a test bench before pump installation. Pump pressure adjustments should not be attempted while pump is installed on the airplane because of the internal bleed characteristics of the hydraulic system. Pump pressure adjustments are made under zero flow conditions.
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