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C.  Case Drain Filters
(1)  A case drain filter installed in each electric motor-driven pump case return line (Fig. 2) is provided to detect incipient failures of a hydraulic pump, and therefore prevent contamination of the reservoir and possible damage to the remaining hydraulic pump. The filters are installed near the pumps in the wheel well, and consist of a filter head, filter element and a filter bowl (Fig. 4).
6.  System B Hydraulic Fluid Heat Exchanger
A.  A hydraulic fluid to fuel heat exchanger is provided to cool the hydraulic fluid by transferring heat from it to the fuel. The heat exchanger is in the pump case return line common to both system B hydraulic pumps, and consists of two coils of tubing mounted in the bottom of the No. 2 fuel tank. Fluid circulates through the heat exchanger whenever system B hydraulic pumps are in operation. The heat exchanger fluid inlet and outlet ports are in the fuel tank wing rear spar (Fig. 5).
7.  System B Relief Valve
A.  The cartridge type system B relief valve installed in the 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.
8.  Pump Ground Fault Protection Controller
A.  The pump ground fault protection controllers for No. 1 and 2 systems are located aft of the P6-1 circuit breaker panel. When 3-phase power to the pump is interrupted or power is grounded in the pump, a sensor located in the 3-phase circuit trips a relay in the controller causing the pump relay to open (Fig. 2). A reset button on the controller is provided to reset the relay after the controller has been tripped. The reset button should not be reset until the failure has been repaired.
551 
29-12-0 Page 8  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  May 01/75 

EFFECTIVITY
AIRPLANES WITH 65-44571-XX HEAT EXCHANGES

F87525
569  System B Hydraulic Fluid Heat Exchanger 
Jun 20/87  Figure 5 (Sheet 1)  29-12-0 
Page 9 

BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.

EFFECTIVITY
AIRPLANES WITH S2714N401-X HEAT EXCHANGERS

System B Hydraulic Fluid Heat Exchanger  569 
29-12-0  Figure 5 (Sheet 2)  Jun 20/87 
Page 10 

BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.

9.  System B Operation
A.  System B reservoir supplies a positive flow of fluid to the electric motor-driven pumps (Fig. 2). Two switches on the pilots' overhead panel control the two electric motor-driven pumps. Positioning the switches to ON energizes the 28-volt dc relay connecting 115-volt, 3-phase ac power to the pump motors. The pumps supply fluid through a pressure filter to the hydraulic-operated systems upon demand. The pumps start at full volume flow. As pressure increases to 1200 +250 psi, the pump low pressure warning switch is actuated opening the circuit to the pump low pressure warning light. As pressure increases, the pressure transmitter senses the increase and electrically positions the pressure indicator on the first officer's panel. As system pressure approaches 3000 psi the pumps automatically adjust output to the need of the system. If system pressure increases to 3500 +50 psi the system relief valve will open to reduce pressure, then reset at 3400 psi. At low pump output, fluid circulates through the pump and back to the reservoir through a case drain filter, heat exchanger and return filter. To shutdown the electric motor-driven pumps the pump switches are positioned to OFF.
569 
Jun 20/87  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  29-12-0 Page 11 

HYDRAULIC SYSTEM B - TROUBLE SHOOTING
1. General
A.  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 each component, hydraulic fitting and connecting line. Pin hole leaks may be detected by noting damp spots on hydraulic components, tubing or on the airplane, and tracing run back fluid to locate source of leak. When disconnecting lines and units 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 Chapter 12, Cleaning and Washing.
B.  Illumination of No. 1 or No. 2 pump low pressure warning light during operation of system B and a confirmation of loss of pressure on the affected pump should be followed by a check of the corresponding pump pressure and case drain return filters. Contaminated filter elements indicate a defective pump. The 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.
　
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