B737-3 ATA 29 L3 e

ATA 104 Level 3

Book No: B737-3 29 L3 E

Lufthansa

Lufthansa BaseFor Training Purposes Only

Lufthansa 1995Technical Training GmbH

Training ManualB 737-300/400/500

ATA 29Hydraulic Power

For training purpose and internal use only.

Copyright by Lufthansa Technical Training GmbH.

All rights reserved. No parts of this trainingmanual may be sold or reproduced in any formwithout permission of:

Lufthansa Technical Training GmbH

Lufthansa Base Frankfurt

D-60546 Frankfurt/Main

Tel. +49 69 / 696 41 78

Fax +49 69 / 696 63 84

Lufthansa Base Hamburg

Weg beim Jger 193

D-22335 Hamburg

Tel. +49 40 / 5070 24 13

Fax +49 40 / 5070 47 46

TABLE OF CONTENTS

B737-3 29 L3 E

Page iFRA US/T Sep 2002

ATA 29 HYDRAULIC POWER 1. . . . . . . . . . . . . . . . .

29-00 GENERAL 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . HYDRAULIC POWER SYSTEM INTRODUCTION 2. . . . . . . . . . . . . . . . HYDRAULIC POWER DISTRIBUTION 6. . . . . . . . . . . . . . . . . . . . . . . . . . PANEL DESCRIPTION 8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PANEL DESCRIPTION (CONT.) 10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . HYDRAULIC POWER SYSTEMS COMP. LOCATIONS 14. . . . . . . . . . . . RESERVOIR PRESSURIZATION 16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . RESERVOIR PRESSURIZATION (CONT.) 18. . . . . . . . . . . . . . . . . . . . . . .

29-10 MAIN 20. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . HYDRAULIC SYSTEM A 20. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SYSTEM A CONTROL AND MONITORING 20. . . . . . . . . . . . . . . . . . . . . SYSTEM A DISTRIBUTION 24. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . HYDRAULIC SYSTEM A RESERVOIR 26. . . . . . . . . . . . . . . . . . . . . . . . . .

29-30 INDICATING 28. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . HYDRAULIC FLUID QUANTITY SYSTEM A 28. . . . . . . . . . . . . . . . . . . . . HYDRAULIC FLUID QUANTITY SYSTEM A 30. . . . . . . . . . . . . . . . . . . . .

29-10 MAIN (CONT.) 32. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SYSTEM A HYDRAULIC FLUID SHUTOFF VALVE 32. . . . . . . . . . . . . . . ENGINE DRIVEN PUMP (EDP) 34. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ENGINE DRIVEN PUMP CONTROL 36. . . . . . . . . . . . . . . . . . . . . . . . . . . . ELECTRIC MOTOR DRIVEN PUMP (EMDP) 38. . . . . . . . . . . . . . . . . . . . ELECTRIC MOTOR DRIVEN PUMP CONTROL 40. . . . . . . . . . . . . . . . . . SYSTEM A CASE DRAIN FILTER 42. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SYSTEM A HEAT EXCHANGER 44. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

29-30 INDICATING (CONT.) 46. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SYSTEM A OVERHEAT LIGHT (ABEX PUMP) 46. . . . . . . . . . . . . . . . . . . SYSTEM A OVERHEAT LIGHT (VICKERS PUMP) 46. . . . . . . . . . . . . . . ELECTRIC MOTOR DRIVEN PUMP ACUSTIC FILTER 48. . . . . . . . . . . SYSTEM A PRESSURE MODULE 50. . . . . . . . . . . . . . . . . . . . . . . . . . . . .

29-30 INDICATING (CONT.) 52. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SYSTEM A LOW PRESSURE WARNING 52. . . . . . . . . . . . . . . . . . . . . . . PRESSURE INDICATION CIRCUIT - SYSTEM A 54. . . . . . . . . . . . . . . .

29-10 MAIN (CONT.) 58. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SYSTEM A RETURN FILTER 58. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . HYDRAULIC SYSTEM B 62. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SYSTEM B CONTROL AND MONITIRING 62. . . . . . . . . . . . . . . . . . . . . . SYSTEM B DISTRIBUTION 66. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SYSTEM B HYDRAULIC RESERVOIR 68. . . . . . . . . . . . . . . . . . . . . . . . . .

29-30 INDICATING (CONT.) 70. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . HYDRAULIC FLUID QUANTITY SYSTEM B 70. . . . . . . . . . . . . . . . . . . . .

29-10 MAIN (CONT) 74. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SYSTEM B HYDRAULIC FLUID SHUTOFF VALVE 74. . . . . . . . . . . . . . . SYSTEM B HYDRAULIC PUMP CONTROL 76. . . . . . . . . . . . . . . . . . . . . SYSTEM B CASE DRAIN COMPONENTS 78. . . . . . . . . . . . . . . . . . . . . . SYSTEM B COMPONENTS 80. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

29-30 INDICATING (CONT.) 84. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PRESSURE INDICATION CIRCUIT - SYSTEM B 84. . . . . . . . . . . . . . . . .

29-20 AUXILIARY 88. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . POWER TRANSFER UNIT (PTU) 88. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . POWER TRANSFER UNIT (PTU) CONTROL 90. . . . . . . . . . . . . . . . . . . . POWER TRANSFER UNIT COMPONENTS 92. . . . . . . . . . . . . . . . . . . . . POWER TRANSFER UNIT (PTU) CONTROL 94. . . . . . . . . . . . . . . . . . . . STANDBY HYDRAULIC POWER 96. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . STANDBY SYSTEM CONTROL AND MONITORING 98. . . . . . . . . . . . . STANDBY SYSTEM DISTRIBUTION 100. . . . . . . . . . . . . . . . . . . . . . . . . . . STANDBY HYDRAULIC RESERVOIR 102. . . . . . . . . . . . . . . . . . . . . . . . . . .

29-30 INDICATING (CONT.) 104. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . STANDBY HYDR. SYSTEM LOW QUANTITY LIGHT 104. . . . . . . . . . . .

29-20 AXILIARY (CONT.) 106. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . STANDBY SYSTEM HYDRAULIC PUMP 106. . . . . . . . . . . . . . . . . . . . . . . . STANDBY HYDRAULIC PUMP CONTROL - MANUAL 108. . . . . . . . . . . . STANDBY HYDR. PUMP CONTROL - AUTOMATIC 110. . . . . . . . . . . . . . STANDBY SYSTEM PRESSURE MODULE 112. . . . . . . . . . . . . . . . . . . . .

29-30 INDICATING (CONT.) 114. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . STANDBY SYSTEM LOW PRESSURE WARNING 114. . . . . . . . . . . . . . .

TABLE OF CONTENTS

B737-3 29 L3 E

Page iiFRA US/T Sep 2002

29-10 MAIN (CONT.) 116. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . GROUND HYDRAULIC FLUID SERVICING - LOCATION 116. . . . . . . . . HYDRAULIC FLUID SERVICING 118. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . GROUND SERVICE DISCONNECTS 120. . . . . . . . . . . . . . . . . . . . . . . . . . . GROUND CART PRESSURE AND RETURN 122. . . . . . . . . . . . . . . . . . . .

TABLE OF FIGURES

B737-3 29 L3 E

Page iiiFRA US/T Sep 2002

Figure 1 Hydraulic Power System 3. . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 2 Hydraulic System Schematic Symbols 5. . . . . . . . . . . . . . . Figure 3 Hydraulic System Power Distribution 7. . . . . . . . . . . . . . . . . Figure 4 Panel Description 9. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 5 Panel Description (cont.) 11. . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 6 System Schematic 13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 7 Component Locations 15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 8 Reservoir Pressurization 17. . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 9 Reservoir Pressurization Components Location 19. . . . . . . Figure 10 System A Control and Monitoring 21. . . . . . . . . . . . . . . . . . . Figure 11 System A Control and Monitoring 23. . . . . . . . . . . . . . . . . . . Figure 12 System A Distribution 25. . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 13 Hydraulic System A Reservoir 27. . . . . . . . . . . . . . . . . . . . . Figure 14 Hydraulic Fluid Quantity Syststem A 29. . . . . . . . . . . . . . . . Figure 15 Hydraulic Fluid Quantity System A 31. . . . . . . . . . . . . . . . . . Figure 16 System A Hydraulic Fluid Shutoff Valve 33. . . . . . . . . . . . . Figure 17 Engine Driven Pump (EDP) - Vickers 35. . . . . . . . . . . . . . . Figure 18 Engine Driven Pump Control 37. . . . . . . . . . . . . . . . . . . . . . . Figure 19 Electric Motor Driven Pump (EMDP) 39. . . . . . . . . . . . . . . . Figure 20 Electric Motor Driven Pump Control 41. . . . . . . . . . . . . . . . . Figure 21 EDP Case Drain Filter 43. . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 22 System A Heat Exchanger 45. . . . . . . . . . . . . . . . . . . . . . . . Figure 23 Hydraulic Fluid Overheat Warning 47. . . . . . . . . . . . . . . . . . Figure 24 Electric Motor Driven Pump Acustic Filter 49. . . . . . . . . . . . Figure 25 System A Pressure Module 51. . . . . . . . . . . . . . . . . . . . . . . . Figure 26 System A Low pressure Warning 53. . . . . . . . . . . . . . . . . . . Figure 27 Pressure Indicating Circuit 55. . . . . . . . . . . . . . . . . . . . . . . . . Figure 28 Pressure Indicating Circuit 57. . . . . . . . . . . . . . . . . . . . . . . . . Figure 29 System A Return Filter 59. . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 29 Hydraulic System A Summary 61. . . . . . . . . . . . . . . . . . . . . Figure 30 System B Control and Monitoring 63. . . . . . . . . . . . . . . . . . . Figure 31 System B Control and Monitoring 65. . . . . . . . . . . . . . . . . . . Figure 32 System B Distribiution 67. . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 33 System B Hydraulic Reservoir 69. . . . . . . . . . . . . . . . . . . . . Figure 34 Hydraulic Fluid Quantity System B 71. . . . . . . . . . . . . . . . . .

Figure 35 Hydraulic Fluid Quantity Systtem B 73. . . . . . . . . . . . . . . . . Figure 36 System B Hydraulic Supply Shutoff Valve 75. . . . . . . . . . . . Figure 37 System B Hydraulic Pump Control 77. . . . . . . . . . . . . . . . . . Figure 38 System B Case Drain Components 79. . . . . . . . . . . . . . . . . Figure 39 System B Components 81. . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 40 Hydraulic System B Summary 83. . . . . . . . . . . . . . . . . . . . . Figure 41 Pressure Indicating Circuit 85. . . . . . . . . . . . . . . . . . . . . . . . . Figure 42 Pressure Indicating System 87. . . . . . . . . . . . . . . . . . . . . . . . Figure 43 Power Transfer Unit 89. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 44 Power Transfer Unit Control 91. . . . . . . . . . . . . . . . . . . . . . . Figure 45 Power Transfer System Components 93. . . . . . . . . . . . . . . Figure 46 Power Transfer Unit (PTU) Control 95. . . . . . . . . . . . . . . . . Figure 47 Standby Hydraulic Power 97. . . . . . . . . . . . . . . . . . . . . . . . . Figure 48 Standby System Control and Monitoring 99. . . . . . . . . . . . . Figure 49 Standby System Distribution 101. . . . . . . . . . . . . . . . . . . . . . . Figure 50 Standby Hydraulic Resevoir 103. . . . . . . . . . . . . . . . . . . . . . . Figure 51 Standby Hydraulic System Low Quantity Light 105. . . . . . . Figure 52 Standby Pump 107. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 53 Standby Hydraulic Pump Control Circuit 109. . . . . . . . . . . . . Figure 54 Standby Hydraulic Pump Control - Automatic 111. . . . . . . . Figure 55 Standby System Pressure Module 113. . . . . . . . . . . . . . . . . . Figure 56 Standby Sysstem Low Pressure Warning 115. . . . . . . . . . . . Figure 57 Ground Hydraulic Fluid Sevicing Location 117. . . . . . . . . . . Figure 59 Hydraulic Fluid Servicing 119. . . . . . . . . . . . . . . . . . . . . . . . . . Figure 60 Ground Sevice Disconnects 121. . . . . . . . . . . . . . . . . . . . . . . Figure 61 Ground Cart Return & Pressure 123. . . . . . . . . . . . . . . . . . .

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HYDRAULIC POWER B737-300/400/500

Page: 1HAM US/E sp Sep 96

ATA 29 HYDRAULIC POWER

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HYDRAULIC POWERGENERAL

B737-300/400/500

29-00


29-00 GENERALHYDRAULIC POWER SYSTEM INTRODUCTION

PurposeThree separate and independent hydraulic systems are provided to power theflight controls, landing gear and thrust reversers.

System DescriptionThe hydraulic systems are identified as system A, system B and standby.System A and System B are full-time operating systems during flight thatshare responsibility for all hydraulically powered components.The standby system is operated only on demand.System A and B each include an engine driven pump (EDP) and an electricmotor driven pump (EMDP). The output pressure from the two pumps of eachsystem is routed to the using system.The three hydraulic systems use BMS 3-11, type IV hydraulic fluid.The Standby System has an electric motor driven pump (EMDP). The outputpressure is routed to the using systems.

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Page: 3HAM US/E sp Sep 96 Page: 3Figure 1 Hydraulic Power System

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B737-300/400/500

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THIS PAGE INTENTIONALLY LEFT BLANK

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B

BEING SHOWNPART OF SYSTEMLRU WHICH IS NOT

BEING SHOWNPART OF SYSTEMLRU WHICH IS

FLUID COOLEDFINNED TYPE,HEAT EXCHANGER-

PRESSURE INDICATORBYPASS & DIFFERENTIALFILTER WITH

VALVECHECK

WITH CAPVALVECHARGING

VALVERELIEFPRESSURE

VALVESHUTTLE

VALVEDEPRESSURIZATIONRESERVOIR

SENSORTEMPERATURE

PRESSURE SENSOR

FILTER

(BOTH DIRECTIONS)FLOW RESTRICTOR

(ONE DIRECTION ONLY)FLOW LIMITER

HYDRAULIC FUSE

DISCONNECT(OR QUICK TYPE)SELF-SEALING

VALVESHUTOFFOPERATEDMOTOR

PRESSURE

RETURN

SUPPLY

AIR

VALVESHUTOFFMANUAL

t95055

Page: 5Figure 2 Hydraulic System Schematic Symbols

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HYDRAULIC POWER DISTRIBUTION

System InterfacesThree independent hydraulic systems: A, B and standby generate all necessaryhydraulic power and provide system redundancy.Three separate reservoirs provide hydraulic fluid to the pumps. The system Aand B reservoirs are not interconnected. The standby and system B reservoirsare connected by a balance line.

Reservoir Pressurization SystemAir pressure from the pneumatic system ducts is routed through a pressuriza-tion module to the system A and B reservoirs. This maintains a head pressureon the three reservoirs to provide constant supply of fluid to the pumps andprevent foaming in the reservoirs.

System AThe pressure sources for system A are one engine driven pump (EDP) on theleft engine and one electric motor driven pump (EMDP) in the main wheel well.Both pumps normally operate in-flight to power the primary flight controls, in-board flight spoilers, ground spoilers, landing gear and the left thrust reverser.System A can be used as an alternate source of brake pressure.

Power Transfer UnitThe power transfer unit (PTU) is a hydraulic motor pump assembly that pro-vides an alternate power source for autoslat operation if system B EDP pres-sure is lost. System A drives the motor when required and the pump pressur-izes fluid obtained from the system B reservoir.

System BSystem B sources are the right engine driven pump (EDP) and one electric mo-tor driven pump (EMDP) in the main wheel well.Both pumps normally operate in-flight to power the primary flight controls, out-board flight spoilers, trailing edge flaps, leading edge flaps and slats, brakesand the right thrust reverser. System B can be used for alternate gear retrac-tion.

Standby SystemStandby is an on-demand system providing reserve hydraulic power for theoperating systems of rudder, thrust reversers and leading edge devices. Thepressure source for the standby system is an electric motor-driven pump(EMDP).

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B737-300/400/500

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104830

2.8 USG

ELEV

LEADING

FLOW RESTRICTOR

ACCUMULATOR

(0,1,4,5,8,9)

PRESS.SYS.

BALANCE LINE

MOTOR

TRANSFERPOWER

EMDPEMDP

SYSTEM BSYSTEM A

SPOILERS

CONTROL OR

RESERVOIR

VALVEFILL SELECT

RESERVOIRReservoirRESERVOIR

MAIN GEAR& STEERINGNOSE GEAR

EDPEDP

EDGE FLAPSTRAILING

BRAKES

2 & 7SPOILERS

FLT

SLATS/FLAPSEDGE

UNIT (PTU)

PUMP

MODPRESSSYS B

FEEL

ELEVATOR

AUTOPILOT

AILERONS

REVERSERTHRUST

LEFT

REVERSERTHRUSTRIGHT

RUDDERSTANDBY

SystemStandby

PRESS MODRESERVOIR

CHECK VALVE

SHUTTLE VALVE

PRIORITY VALVE

GRD

3 & 6SPOILERS

FLT

MODPRESSSYS A

EMDP

4.7 USG 7.2 USG

SV

AUTOPILOT

norm

norm

alt retr

PV

CV

CV

SV

PV

ACV

SV

N2 ENG 2N2 ENG 1

M M M

TOTAL HYDRAULIC QUANTITY

A-SYSTEM B- AND STANDBYSystem

13 USG

aprox. 49 Ltr.

20 USG

aprox. 76 Ltr.

No.1No.2 No.1No.2

CV

SV CVauto

SHUTOFF VALVE

alt

SV SV

SYSTEM A ONLY

only

GEAR DOWN LINE

RUDDER

MOD.

CV

CV

FROM PNEUMATICSYSTEM

FROM PNEUMATICSYSTEM

Page: 7Figure 3 Hydraulic System Power Distribution

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PANEL DESCRIPTION

1 FLT Control Switches A & B- OFF - Corresponding hydraulic system pressure to ailerons, elevators

and rudder is shutoff- STDBY RUD - (either switch) Corresponding hydraulic system pressure

to ailerons, elevators and rudder is shutoff. Turns on standby pump,opens standby rudder shutoff valve and pressurizes standby rudderpower control unit.

- ON - (guarded position) Normal operation.

2 FLT Control Low Pressure Lights (amber)- ON - Indicates low pressure of corresponding hydraulic system to aile-

rons, elevator and rudder. MASTER CAUTION light and FLT CONT an-nunciator illuminate.

- Deactivated when corresponding flight control switch is positioned toSTDBY RUD and the standby rudder shutoff valve is open.

3 Standby Low Quantity Light (amber)- ON - Indicates low fluid level (< 1.4U.S.gallons) in hydraulic standby sys-

tem

4 Standby Low Pressure Light (amber)- ON - Indicates low output pressure of electric motor driven standby

pump.- Armed only when standby pump operation has been selected or auto-

matic standby function is activated.

5 Alternate Flaps Master Switch- ARM - Closes trailing edge flap bypass valve, turns on standby pump,

arms alternate flaps position switch and arms standby hydraulic LOWPRESSURE light.

- OFF - (guarded position) - Normal operation

6 Engine Driven Pump Switches A & B- ON - De-energizes blocking valve in pump to allow pump pressure to

enter system- Should remain ON at shutdown to prolong solenoid life.- OFF - Energizes blocking valve to block pump output.

7 Elec Driven Pump Switches A & B- ON - Provides power to corresponding electric motor driven pump.

8 Engine Driven Pump Low Pressure Lights (amber)- ON - Output pressure of corresponding engine driven pump is low

(

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OFF OFF

A ON

OFF

ON ON

OFF

CONTROL AND FAULT INDICATION

STANDBY SYSTEM PUMP

SYSTEMS A AND B PUMP

P5 PANEL

P5 PANEL

YAW DAMPER

FAIL

SPOILER

STDBY

FAIL

OFF

DAMPERYAW

FAIL

FEEL DIFF

AUTO SLAT

ON

MACH TRIM

SPEED TRIM

PRESSOFF

QUANTITYLOW

PRESSURELOW

PRESSURELOW

OFF

OFF

RUD

PRESSURELOW

STDBYRUD

ARM

DOWN

OFF

UP

B ON

BA

B

ALTERNATE FLAPS

HYD

STANDBYFLT CONTROL

A

HYD PUMPS

LOW

ON

PRESSURE

ENG 2ELEC 1

OVERHEAT

PRESSURELOW

PRESSURELOWLOW

ENG 1 ELEC 2

A

ON

PRESSURE

OVERHEAT

B

1

2

3

4

5

67

89

110

6

8

10

RIGHT LIGHT SHIELD HYDRAULIC FAULT LIGHT

PUSH TO RESET BELL CUTOUT

WARNFIRE

CAUTIONMASTER

ANTI-ICE ENG

HYD

DOORS AIR COND

OVERHEAD

Page: 9Figure 4 Panel Description

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B737-300/400/500

29-00


PANEL DESCRIPTION (CONT.)

11 Hydraulic Brake Pressure Indicator- Indicates hydraulic brake pressure measured at brake pressure accumu-

lator.- Indicates accumulator precharge pressure plus residual hydraulic pres-

sure prior to activation of any hydraulic pump.- Nominal pressure - 3000 psi- Maximum pressure - 3500 psi- Normal precharge - 1000 psi

12 Hydraulic System Pressure Indicator - Indicates hydraulic system A and B pressure- Nominal pressure - 3000 psi- Maximum pressure - 3500 psi- During system failure indicator pointer remains on last value.

13 Hydraulic System Quantity Indicators- System A - F (Full) 4.8 U.S.gallons- RFL (Refill) 4.2 U.S.gallons- System B - F (Full) 7.2 U.S.gallons- RFL (Refill) 6.4 U.S.gallons- During system failure indicator pointer moves out of range to a value be-

low E.

14 System Pressure Indication- System pressure gages, for System A and System B, are located on the

Secondary Engine and Hydraulic Display.

15 Quantity Indication- Individual digital quantity readouts, in percent of full, will be displayed on

the Secondary Engine and Hydraulic Display for System A and SystemB reservoirs.

Airplanes without engine instrument system.

Airplanes with engine instrument system2

1

1

2

2

1

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PRESS

PSI X 1000

1

0

4

3

HYD SYS

SYS B

RFL

E

HYD QTY

12 3

4

F

41

RFL

E

HYD QTY

SYS A

12 3

4

F

41

1

1 1

11

12

1313

SECONDARY ENGINE AND HYDRAULIC DISPLAY (P2)

2

14

1515

14

1 AIRPLANE WITHOUT ENGINEINSTRUMENT SYSTEM

2 AIRPLANE WITH ENGINEINSTRUMENT SYSTEM

Page: 11Figure 5 Panel Description (cont.)

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Page: 12

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B

B

PRESSURE MODULE

SYSTEM A

RESERVOIR

SYSTEM B

RESERVOIR

STANDBY

PRESSURE MODULE

STANDBY SYSTEM

DUCT

PNEUMATIC

FROM RIGHT

DUCT

PNEUMATIC

FROM LEFT

RDV RDV

SELECTOR VALVE

RESERVOIR FILL

FLOW

RETURN

EMDP

EMDP

EDP

FUEL

EDGE FLAPS

TRAILING

2 & 7

FLT SPOILERS

RUDDER

STANDBY

MODULE

SYSTEM B PRESSURE

MODULE

CONTROL

FLIGHT

SYSTEM B

DEVICES

LEADING EDGE

AUTOPILOT

AILERONSAILERONS

REVERSER

RIGHT THRUST

REVERSER

LEFT THRUST

YAW DAMPER

RUDDER AND

FEEL

ELEVATOR

AUTOPILOT

ELEVATORS

BRAKES

ELEVATORS

GEAR

LANDINGSPOILERS

GROUND

EMDP

DISCONNECT

GROUND SERVICE

3 & 6

FLT SPOILERS MODULE

CONTROL

FLIGHT

SYSTEM A

EDP

FUEL

EXCHANGER

HEAT

RESERVOIR

SYSTEM A

FILTER MODULE

SYSTEM A RETURN

FILL PORT

PRESSURE

NOZZLE

FLEX HOSE WITH

PUMP

HAND OPERATE

FILTER MODULE

SYSTEM B RETURN

EXCHANGER

HEAT

UNIT

TRANSFER

POWER

FLOW

RETURN

SYSTEM B

DISCONNECT

GROUND SERVICE

FLOW

RETURN

SYSTEM A

t95136

Page: 13Figure 6 System Schematic

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Page: 14HAM US/E Sep 96

HYDRAULIC POWER SYSTEMS COMP. LOCATIONS

General Component LocationsThe major components for control and monitoring of the three hydraulic sys-tems are located in the main landing gear wheel well area.The engine driven pumps (EDP) are located on the engine accessory gear box.

General System FeaturesThree separate and independent hydraulic systems provide fluid pressurized toa nominal 3000 psi.The two primary hydraulic Systems A and B are each powered by one enginedriven pump and one 115-volt ac electric motor driven pump. System A is sup-plied by the left engine driven pump and System B by the right engine drivenpump.Both electric motor driven pumps and most of the other hydraulic componentsare located in the main gear wheel well area. These consist of:

- System A and B hydraulic fluid shutoff valves.- System A, B and Standby reservoirs.- System A, B and Standby Pressure modules.- System A and B return filter modules.- Manual reservoir fill pump,- Pressure fill connection and servicing filter.

A Reservoir Pressurization module provides filtered air to all three hydraulicsystem reservoirs.A single electric motor driven pump powers the Standby System, which isavailable when required to operate the rudder, thrust reversers and extend theleading edge flaps and slats. The pump is located on the keel beam in the maingear wheel well.Control switches and indicators for the three hydraulic systems are located inthe flight compartment.

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SYSTEM B RETURN

PRESSURE MODULE

SYSTEM EMDP

STANDBY SYSTEMRESERVOIR

STANDBY

FILTERCASE DRAINSTANDBY EMDP

MODULEPRESSURESTANDBY

MODULERETURN FILTERSYSTEM A

SYSTEM A

PRESSURE MODULESYSTEM B

SYSTEM B

SYSTEM B EMDP

SYSTEM A EMDP

RESERVOIRSYSTEM A

PUMPMANUAL FILL

POWER TRANSFER UNIT (PTU)

PTU PRESSURE FILTER

PRESSURE FILTER

FILTER MODULE

CONNECTIONPRESSURE FILL

RESERVOIR FILL

RESERVOIR

MODULEPRESSURIZATIONRESERVOIR

(TYP)EDP

104831

Page: 15Figure 7 Component Locations

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RESERVOIR PRESSURIZATION

PurposeThe three hydraulic reservoirs are pressurized to45 - 50 psi by the pneumatic system to provide a positive fluid flow from thereservoir to the pumps and maintain normal return pressure in the hydraulicsystem.The pneumatic manifold, left and right ducts and reservoir pressurization mod-ule receive temperature and pressure-limited air from both engine bleeds, theAPU or a ground pneumatic cart.

Component LocationThe reservoir pressurization components are located in the vicinity of the for-ward bulkhead of the right main wheel well.

System DescriptionThe reservoir air is provided from the pneumatic manifold consisting of the leftand right, or APU pneumatic ducts. The reservoir pressurization module is themajor component and contains check valves, a filter, an orifice assembly, an aircharging valve and a test port. Also, included in the system are vents, restric-tors, reservoir depressurization valves, pressure gages and pressure reliefvalves.

Reservoir PressurizationThe reservoir pressurization module provides filtered air to all hydraulic systemreservoirs any time the pneumatic manifold is pressurized. The manifold maybe pressurized from either or both engine bleeds, APU bleed, or external air.Air pressure gages provide an indication of air pressure in the respective reser-voir.The reservoir pressurization module provides filtered air to all hydraulic systemreservoirs any time the pneumatic manifold is pressurized. The manifold maybe pressurized from either or both engine bleeds, APU bleed, or external air.Air pressure gages provide an indication of air pressure in the respective reser-voir.A pressure relief valve, installed near each S;stem A and B reservoir, opensunder high air or fluid pressure to protect the reservoir.

One restrictor orifice and one vent is in each incoming and outgoing line to thereservoir pressurization module. Their restriction will prevent a noticeable lossof pneumatic duct pressure should a down stream break in the system occur.The vents continually force contaminates out of the pressurization system.A reservoir depressurization valve in the line to each main hydraulic reservoircan be manually opened to relieve air pressure from the respective reservoir.The Standby System reservoir is depressurized simultaneous with the SystemB reservoir.

Restrictors (Airplanes without the reservoir balance line)One restrictor orifice and one vent (with orifice) is positioned in each incomingand outgoing line. The two outgoing restrictors are installed in an orifice assem-bly which is attached to the reservoir pressurization module. Their restrictionwill prevent a noticeable loss of pneumatic duct pressure should a downstreambreak in the system occur.

Restrictors (Airplanes with the reservoir balance line)One restrictor and one vent are positioned in each incoming line. The outgoinglines contain a vent and a tee valve assembly. The tee valve assembly containsa single check valve and a restrictor for each outgoing line. The restrictors willprevent a noticeable loss of pneumatic duct pressure should a downstreambreak in the system occur.

Air Pressure GagesA pressure gage for each System A and B reservoir provides an indication ofair pressure.A pressure gage calibrated in pounds per square inch is located between eachreservoir depressurization valve and its respective reservoir.

Pressure Relief ValvesA pressure relief valve for each main hydraulic system reservoir opens underhigh air or fluid pressure (60-65 psi) to protect the reservoir.A pressure relief valve is installed downstream of each reservoir depressuriza-tion valve near the reservoir air inlet.

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VENT

TEST PORTVALVEAIR CHARGINGMANUAL

(EXAMPLE)RESTRICTORFILTER

CHECK VALVE

RESERVOIR PRESSURIZATION MODULE

VENT

VALVEISOLATIONBLEED AIR

RIGHT PNEUMATIC DUCTLEFT PNEUMATIC DUCT

AIR VALVE

APU BLEED

FROM APU

ORIFICE ASSEMBLY

RESTRICTOR

(VENT) VALVEDEPRESSURIZATIONRESERVOIR

AS SHOWN)SYSTEM B(SIMILAR TORESERVOIRTO SYSTEM A

1

TEE VALVE ASSEMBLY

AIRPLANES WITH RESERVOIR BALANCE LINE1

Page: 17HAM US/E sp Jul 97Figure 8 Reservoir Pressurization

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RESERVOIR PRESSURIZATION (CONT.)

Reservoir Pressurization ModuleA reservoir pressurization module centralizes the functions of routing pressureto the System A and B reservoirs, air charging pressure bleeding and filtration.The reservoir pressurization module is installed on a bracket mounted on theforward wheel well bulkhead.Check valves prevent loss of pressure at the failure of either or both pressuresources.A test port provides for attachment of a pressure source for maintenance or forinstallation of a gage for test purposes.A manual bleed/air charging valve allows ground pressurization of the reser-voirs for maintenance.The cleanable filter prevents downstream contamination of the system.The pneumatic manifold must be depressurized prior to removal/installation ofthe reservoir pressurization module or servicing of the pressurization systemfilter.

Depressurization Valve (Airplanes without the reservoir balance line)A manually controlled depressurization (vent) valve for each A and B system islocated between the reservoir and the reservoir pressurization module. Checkvalves contained inside the depressurization valve are positioned to blockpneumatic system pressure when a slide in the valve is held in a position tovent the reservoir. A valve lock can be installed over a maintenance period,requiring removal to return the system to operational (pressurized) status. Thecheck valves also operate to retain a working pressure within the reservoirshould upstream pressure fail. The standby reservoir pressure is transmittedthrough the balance line from the system B reservoir.

Depressurization Valve (Airplanes with the reservoir balance line)A manually controlled depressurization (vent) valve for each A and B system islocated between the reservoir and the reservoir pressurization module. A valvelock can be installed over a maintenance period, requiring removal to return thesystem to operational (pressurized) status. The standby reservoir pressure istransmitted through the balance line from the system B reservoir.

WARNING: FAILURE TO DEPRESSURIZE PNEUMATIC MANIFOLD MAYRESULT IN INJURY TO PERSONNEL AND DAMAGE TOEQUIPMENT.

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FWDINBD

A

SUPPLY LINEPNEUMATIC

TO THERESERVOIRS

(2 LOCATIONS)

BULKHEAD

WHEELWELL

REDUCER(2 LOCATIONS)

DEPRESSURIZATION

FILTER

VENT CAP

VALVE (2 LOCATIONS)

TEE

ORIFICE ASSEMBLY

(2 LOCATIONS)

(TEST PORT)

CHECK VALVERESERVOIRD

C

ASEE

VENT CAP

RESERVOIR

PRESSURE GAGEFOR THE SYSTEM B

RESERVOIR

SYSTEM ARESERVOIR

FORWARDBULKHEAD(REF) RESERVOIR

PRESSURIZATIONMODULE

SYSTEM BRESERVOIR

PRESSURE GAGEFOR THE SYSTEM A

VENT CAP

KEEL BEAM (REF)

CAP

VALVE

C

1

VALVE

PLUNGER

C

2

PUSH TO RELEASE THE PRESSURE

D

1 VALVE FOR MANUAL AIR PRESSURIZATION(AIRPLANES WITH A STEEL SCREW-TYPE VALVE)

2 VALVE FOR MAUAL AIR PRESSURIZATION(AIRPLANES WITH AN ALUMINUM PLUNGER-TYPE VALVE)

662466

Page: 19Figure 9 Reservoir Pressurization Components Location

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HYDRAULIC POWERMAIN

B737-300/400/500

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Page: 20HAM US/F sp Sep 96

29-10 MAIN

HYDRAULIC SYSTEM A

PurposeSystem A is one of the two full-time hydraulic systems used in-flight.One thrust reverser, the landing gear and approximately half of the flight con-trols are powered by system A

System DescriptionSystem A hydraulic power operates the following systems:

- Landing Gear- Nose Wheel Steering- Left Thrust Reverser- Ailerons - Power Control Units and Autopilot Actuator- Elevators - Power Control Unit and Autopilot Actuator- Elevator Feel- Rudder- Flight Spoilers 3 and 6- Ground Spoilers- Alternate Brakes- Power Transfer Unit

SYSTEM A CONTROL AND MONITORING

General Subsystem FeaturesSystem A pressure is provided by one engine driven pump and one electricmotor driven pump. A 28 volt DC motor operated shutoff valve in the supplyline between the reservoir and the engine driven pump is normally open.This valve is closed and stops the flow of hydraulic fluid to the engine when thefire handle is pulled.Normal system configuration is with both pumps operating to output fluid pres-surized to 3000 psi through the pressure module to the using systems. Thepressure module contains pressure filters, low pressure switches, check valvesand a pressure relief valve.

Cooling and lubricating fluid from the pumps is filtered and routed through aheat exchanger in the number one fuel tank before entering the reservoir.Return fluid from the using systems is filtered at the return module before en-tering the reservoir.Fluid quantity in the reservoir is displayed on a mechanical gage at the reser-voir and on a remote indicator on the first officers panel (P3) (airplanes withoutEngine Instrument System).Fluid quantity in the reservoir is displayed on a mechanical gage at the reser-voir and as a digital readout in percent of full, on the Secondary Engine andHydraulic Display (airplanes with Engine Instrument System).Pumps are controlled by individual switches on the pilots forward overheadpanel (P5).The pressure output of each pump is monitored by individual pressure switcheson the pressure module. Low pressure at the switch turns on the amber lowpressure light above the respective pump control switch.The electric motor driven pump is monitored for overheat by a temperatureswitch in the case return line and the pump case.Excessive temperature turns on the amber overhead light above the controlswitch.The output of the pressure module is routed to a pressure transmitter in themain wheel well. It transmits total system pressure to the A pointer on thehydraulic system pressure gage located on the first officers panel (P3) (air-planes without Engine Instrument System).The output of the pressure module is routed to a pressure transmitter in themain wheel well. It transmits total system pressure to the System A digitalpressure gage, on the Secondary Engine and Hydraulic Display (airplanes withEngine Instrument System).

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AIRPLANES WITHOUT ENGINE INSTRUMENT SYSTEM

Page: 21Figure 10 System A Control and Monitoring

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Page: 22

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AIRPLANES WITH ENGINE INSTRUMENT SYSTEM

Page: 23Figure 11 System A Control and Monitoring

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SYSTEM A DISTRIBUTION

General OperationPressurized fluid from the two system A pumps is manifolded in the pressuremodule and distributed to the landing gear, flight controls and the left thrust re-verser.

Landing GearSystem pressure is supplied directly to the landing gear transfer valve which isbiased to allow system A pressure to the selector valve for normal extensionand retraction of the landing gear and for nose wheel steering.

Flight ControlsSystem A pressure is supplied directly to the ground spoilers and to two 28-voltdc motor operated shutoff valves in the system A flight control module. Thespoiler shutoff valve, controlled by the spoiler system A switch on the flight con-trol panel, is normally open to provide pressure to the inboard flight spoilers oneach wing (3 and 6). The flight control shutoff valve, controlled by the FlightControl system A switch on the flight control panel, is normally open to providepressure to the primary flight controls, autopilot actuators and the elevator feelsystem. A flight control low pressure switch monitors for low pressure in thesystem.

Left Thrust ReverserThe left thrust reverser is pressurized through two separate lines. Enginedriven pump output is routed directly to the reverser from a tap upstream of thecheck valve in the pressure module. The manifolded output of both pumps isrouted to the reverser through a hydraulic fuse.

Alternate Brake OperationSystem A will provide brake system pressure through the alternate brakesource selector valve if system B is not operating.

Power Transfer Unit (PTU)The PTU provides an alternate power source for leading edge devices opera-tion. System A powers the motor through a control valve when the system Bengine driven pump output is low, flaps are not up and the airplane is in the airmode.

Ground Service DisconnectA ground power module in the left ram air duct bay allows pressure input froma ground hydraulic cart to operate all System A components.

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Page: 25HAM US/E Sep 96 Page: 25Figure 12 System A Distribution

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HYDRAULIC SYSTEM A RESERVOIR

PurposeThe hydraulic reservoir supplies hydraulic fluid to the A system pumps.

LocationThe reservoir is mounted in the upper center area of the main wheel well, nearthe forward bulkhead.

Physical DescriptionThe system A reservoir is an airtight metal shell containing a quantity indicatorand ports for air pressure, return and pump supply lines.The engine driven pump supply line is connected to a standpipe in the reservoirthat prevents use of any fluid below the 1.8 gallon level.The electric motor driven pump can use the entire volume of fluid in the reser-voir.A float-type level quantity transmitter with a direct reading gage is graduatedwith 0 for empty, RFL for refill and F for full.The reservoir should be serviced to the full mark whenever the gage reads RFLor below.The following quantities in US gallons correspond to the scale values:

- 0 for empty 1.0 U.S. gallons- RFL for refill 4.1 U.S. gallons- F for full 4.8 U.S. gallons

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BULKHEAD (REF)

KEEL BEAM (REF)

INDICATOR/

STANDBY

FWD

RESERVOIR

FORWARD

DRAIN/SAMPLING VALVE

EMDP SUPPLY LINEEDP SUPPLY LINE

TRANSMITTER

QUANTITY

MODULEPRESSURIZATIONFROM RESERVOIR

RELIEF VALVERESERVOIR PRESSURE

RESERVOIRSYSTEM A

SYSTEM BRESERVOIR

SEE A

A

LINEVENT

FILL LINERETURN AND

104841

Page: 27Figure 13 Hydraulic System A Reservoir

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HYDRAULIC POWERINDICATING

B737-300/400/500

29-30


29-30 INDICATINGHYDRAULIC FLUID QUANTITY SYSTEM A

Float-type TransmitterA fluid quantity indicating system consists of a floattype level transmitter at thereservoir and two indicators; a direct reading gage on the transmitter and a re-mote gage on the F/O panel (P3).

Remote IndicatorThe remote gage is powered by 28 volts dc. A change in reservoir fluid levelcauses the transmitter float arm to move up or down.The float arm moves a sliding contact of a variable resistor that determines thevoltage applied to coils in the indicator which positions the pointer.A magnet in the indicator moves the indicator pointer off scale when there isno electrical power to the system.

Maintenance PracticesDo not allow float to contact internal standpipe during removal or installation ofthe transmitter to prevent damage.

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Page: 29Figure 14 Hydraulic Fluid Quantity Syststem A

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HYDRAULIC FLUID QUANTITY SYSTEM A

Float-Type TransmitterA fluid quantity indicating system consists of a float-type level transmitter onthe reservoir. The float operates a direct-reading gage on the reservoir. Thetransmitter supplies a signal to a digital quantity readout, in percent of full, onthe Secondary Engine and Hydraulic Display.

Maintenance PracticesDo not allow the transmitter float to contact internal standpipe during removalor installation of the transmitter to prevent damage to the float.Transmitter mounting bolt holes are arranged so that system A and B transmit-ters cannot be interchanged because internal calibrations are different due todifferent reservoir sizes.Engine oil pressure must be less than 11 psi to accomplish a BITE check of thesecondary engine and hydraulic display.

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Page: 31Figure 15 Hydraulic Fluid Quantity System A

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HYDRAULIC POWERMAIN

B737-300/400/500

29-10


29-10 MAIN (CONT.)SYSTEM A HYDRAULIC FLUID SHUTOFF VALVE

PurposeA hydraulic fluid supply shutoff valve is installed in the supply line between thereservoir and engine driven pump.The valve is normally open.The shutoff valve is closed when the number one fire handle is pulled up andshuts off the flow of hydraulic fluid to the engine.

LocationThe system A shutoff valve is located in the wing rear spar area just outboardof the main left wheel well.

Physical DescriptionEDP hydraulic fluid supply valves are operated by 28 volt DC motors only.The system A shutoff valve is controlled by fire handle number one.A position indicator on the valve displays valve position, OPEN or CLSD.These valves cannot be positioned manually.

Maintenance PracticesThe hydraulic reservoir must be depressurized and drained prior to removingthe EDP hydraulic fluid shutoff valve.CAUTION: If either engine No. 1 or 2 fire switches are positioned to FIRE with

the corresponding engine-driven pump operating, proceed with thefollowing steps:

- If a supply shutoff valve was closed for less than 5 minutes, no mainte-nance is required and shutoff periods are not accumulative.

- If supply shutoff valve was closed for longer than 5 minutes, ensurethat pump has operated at least one minute with supply fluid availablebefore checking filter elements so that metal contamination, possiblygenerated during fluid shutoff, has reached the filter. (a) Check casedrain filter element for metal contamination

- Check pressure filter for metal contamination- If no metal is found in either filter, install new filters and continue to run

pump. Recheck filters in 200 hrs.- If metal is found, remove applicable pump for overhaul and flush lines

between the pump and filters.

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HYDRAULIC POWERMAIN

B737-300/400/500

29-10


SEE

P8

DISCHARGE

R BOTTLE

APU

L R

2

E

ENGINES

DISCHARGE

L BOTTLE

DISCH

RLOVERHEAT

ENG 2

NORMAL

BA

OVHT DET

BUTTON UNDER HANDLELOCK OVERRIDE: PRESS

PULL WHEN ILLUMINATED(FUEL SHUTOFF)

FIRE SWITCHESTEST

WHEEL

RL

DISCH DISCH

F

OVERHEATENG 1

OVHT DETBELL CUTOUT

NORMAL

BA

1

TSET

TX

ERIF

THVO

PONI

TLUA

DISCHARGE

APU BOTTLE

INOP

APU DET

FAULT

WELL

EDP SUPPLY

VALVESHUTOFF

ENG NO. 1HYD SOV

NO. 1 ENGINE

NO. 1 ENGINE HYDRAULIC

P8

FLUID SHUTOFF VALVE

CLOSE

OPENFIRE SWITCH

FIRE

NORMAL

BAT. BUS28V DC

A

(ENG 1 SHOWN)

SELECTSRESPECTIVEEDP LOW PRESSLIGHT OFF

A

104846

Page: 33Figure 16 System A Hydraulic Fluid Shutoff Valve

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HYDRAULIC POWERMAIN

B737-300/400/500

29-10


ENGINE DRIVEN PUMP (EDP)

PurposeThe engine driven pump (EDP) is one of the two pressure sources for the Sys-tem A hydraulic system.

LocationThe System A EDP is mounted on the engine accessory drive case of numberone engine.

Physical Description/FeaturesThe EDP is pressure compensated to maintain a nominal 3000 psi output atflow demands of approximately 22-1/2 gpm. The EDP is capable of operating inits normal pumping mode or in a depressurized condition. In its depressurizedmode, the EDP is isolated from the hydraulic system downstream and runs atzero flow.EDP change is facilitated by self-sealing disconnect fittings at the pump thatconnect the supply, case return, and pressure lines. Quick disconnects in theselines at the cowl support beam are used during major engine maintenance.

CAUTION: DO NOT OPERATE EITHER EDP MORE THAN 2 MINUTESUNLESS THE APPLICABLE FUEL TANK CONTAINS ATLEAST 1675 LBS (760KG) OF FUEL. IF PUMPS ARE OPER-ATED 2 MINUTES WITHOUT FUEL IN TANK, ALLOW RES-ERVOIR TO RETURN TO AMBIENT TEMPERATURE BE-FORE RESUMING TEST.

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HYDRAULIC POWERMAIN

B737-300/400/500

29-10


NO. 2 ENGINE SIMILARNO. 1 ENGINE SHOWN1

SEE A 1

FWD

FWD

QAD ATTACH RING

(EXAMPLE)DRAIN PLUG

CASE DRAIN LINE

VALVEDEPRESSURIZATIONPUMP

CONNECTORELECTRICAL

SPLINED SHAFT

DRAIN LINEFOR THESHAFT SEAL

SHAFT BOOT SEALBACKUPWRENCH

DISCONNECTSELF-SEALING

SUPPLY LINE

LINEPRESSURE

O-RING

QAD CLAMP

GASKET

MOUNTING PAD

A

GEAR BOX

126873

Page: 35Figure 17 Engine Driven Pump (EDP) - Vickers

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HYDRAULIC POWERMAIN

B737-300/400/500

29-10


ENGINE DRIVEN PUMP CONTROL

ControlAn engine driven pump operates in the normal pumping mode when the controlswitch (ENG 1) on P5 is in the ON position and the engine is running.Moving the control switch to OFF provides a path for 28 volts dc to energizethe depressurizing solenoid. This opens the depressurizing valve and portspressure to the compensating valve and the blocking valve.The compensator valve opens which allows pump output pressure on the actu-ating piston to move the yoke assembly to the zero displacement position.Equal pressure on both sides of the blocking valve allows the spring to positionit so that the pump is isolated from the downstream portion of the hydraulicsystem.Output of an engine driven pump is not effected by an interruption of electricalpower.Cooling and lubricating fluid circulates through the pump and back to the reser-voir via the case drain line in both modes of operation.Engine driven pump control switches should remain in the ON position exceptwhen a requirement exists to depressurize the pump.

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PUMP SHOWN DEPRESSURZED

PUMP SHOWN PRESSURIZED

Page: 37Figure 18 Engine Driven Pump Control

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Page: 38HAM US/E 96

ELECTRIC MOTOR DRIVEN PUMP (EMDP)

PurposeThe electric motor driven pump is one of the two pressure sources for hydraulicSystem A.

LocationThe System A EMDP is attached on vibration absorbing mounts in the left for-ward wheel well area.

Physical Description/FeaturesThe EMDP assembly is composed of an oil-cooled, three-phase, 115-volt acmotor, a centrifugal pump and a single-stage, variable-displacement, pressure-compensated hydraulic pump. An acoustic filter is fitted in the pressure line tosuppress the noise and vibration of pump operation.Hydraulic fluid enters the pump by way of the electric motor housing providingcooling to the rotor and stator assemblies, before entering the centrifugal boostcavity. From the centrifugal boost pump, the fluid is driven into a barrel cylindercontaining nine pistons, which is revolved adjacent to a cam plate. As the pis-tons reciprocate traveling in the cam track, they are forced to discharge fluid atworking pressure. This pressure is sensed by a compensator valve and springcalibrated to drive the cam plate to a ramp angle which will maintain a supply ofapproximately 6.0 gpm at 2700 psi. The pump also moves fluid through itscase to lubricate and cool the pump.

CAUTION: DO NOT OPERATE EMDP MORE THAN TWO MINUTES UN-LESS THE NO. 1 FUEL TANK CONTAINS AT LEAST 1675LBS (760 KG) OF FUEL. IF PUMP IS OPERATED TWO MIN-UTES WITHOUT REQUIRED FUEL IN TANK, ALLOW RES-ERVOIR TO RETURN TO AMBIENT TEMPERATURE BE-FORE RESUMING PUMP OPERATION.

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Page: 39HAM US/E 96

SYSTEM A EMDP

SYSTEM B EMDP

FWD

WHEEL WELL

KEEL BEAMSEE

SEE

VICKERS EMDP

CASE DRAIN LINE

SUPPLY LINE

ACOUSTIC FILTER

PRESSURE LINE

ELECTRICALCONNECTOR

AIRPLANES WITH VICKERS PUMPS

SYSTEM A EMDP SIMILARSYSTEM B EMDP SHOWN

1

2

2

1 CASE DRAIN LINE

PRESSURE LINE

SUPPLY LINE

GROUNDING STRAP

CONNECTORELECTRICAL

ACOUSTIC FILTER

A

A

A

A

ABEX EMDP

767885767898

Page: 39Figure 19 Electric Motor Driven Pump (EMDP)

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ELECTRIC MOTOR DRIVEN PUMP CONTROL

PurposeThe electric motor driven pump (EMDP) provides a second pressure source forsystem A.

LocationThis EMDP is located below the system A reservoir, near the forward bulkheadof the main wheel well.

Physical Description/FeaturesIt is a 3-phase, 115 volt ac motor driven pump, pressure compensated to main-tain a nominal 3000 psi output at flow demands of approximately six gpm.

ControlThe EMDP is controlled by a switch on the pilots forward overhead panel (P5).When the switch (ELEC 2) is ON, 28 volt dc from BUS 2 energizes a controlrelay that closes three contacts and provides a path for 115 volts ac from BUS2 to the motor. When the switch is OFF, the relay is de-energized and the con-tacts open to stop the motor. A Thermal switch limits excessive temperature inthe motor case by removing the ground for the system A elec hyd pump relay(only Vickers Pump).A pump ground fault detector is located in the P6-1 circuit breaker panel. Whenpower is grounded in the pump such that a 2-4 amp. current differential exists,a current transformer located in the 3-phase circuit trips a relay in the detector.This causes the pump relay to open removing power from the pump. A resetbutton on the detector is provided to reset the relay after the fault has beencorrected.

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1

2 AIRPLANES WITH VICKERS PUMPSOPEN >118 C CLOSE < 38 C

RENDUNDANT COIL

2

Page: 41Figure 20 Electric Motor Driven Pump Control

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SYSTEM A CASE DRAIN FILTER

PurposeA case drain filter is installed in each pump case return line to detect pumpwear and prevent contamination of the system.

LocationThe system A EDP case drain filter is located in the left wing, near the aft, out-board end of the landing gear support beam.The EMDP case drain filter is directly beneath the pump in the main wheel well,left side.A contaminated filter can cause the EMDP overheat light to illuminate.

Physical DescriptionThe filter consists of a noncleanable filter element inside a metal housing. Anarrow on the filter housing indicates direction of flow through the filter. A checkvalve on the outlet of each filter prevents reverse flow from the opposing pump.If a hydraulic system pump is replaced due to malfunction, the respective casedrain filter element must also be replaced.The flaps must be extended at least 10 units with the inboard ground spoiler inthe full up position for access to the EDP filter.

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SYSTEM B EDP CASEDRAIN FILTER

DRAIN FILTERSYSTEM A EDP CASE

CASE DRAIN FILTERSSYSTEMS A AND B EMDP

RESERVOIR (REF)

EMDP (REF)RESERVOIR (REF)

SYSTEM A EMDP (REF)

SEE

SEE

SYSTEM BSYSTEM A

SYSTEM B EMDPCASE DRAIN FILTER

SYSTEM B

CASE DRAIN FILTERSYSTEM A EMDP

TORQUE TUBEFLAP DRIVE

SYSTEM B FILTER SHOWN, SYSTEM A OP-POSITE BELOWGROUND SPOILER NO. 4

IN

FILTER BOWL

(TYPICAL)MOUNTING BOLT

FILTER HEAD

(OUTFLOW SIDE ONLY)CHECK VALVE (TYPICAL)

D CASE DRAIN FILTER

LOCATION BELOW GROUND SPOILER NO. 5

D

D

OUT

OUTIN

Page: 43Figure 21 EDP Case Drain Filter

HAM US/E sp Jul 98

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SYSTEM A HEAT EXCHANGER

PurposeA heat exchanger cools hydraulic fluid before it returns to the reservoir.

LocationIt is mounted in the bottom of the number one fuel tank.

Physical Description/FeaturesThe heat exchanger is in the case return line common to both system Apumps. Fluid circulates through the heat exchanger when either pump is oper-ated and transfers heat from the fluid to the fuel. At least 250 U.S. gallons(1675 lbs) (761 KG) of fuel is required in the number one fuel tank for propercooling.Do not operate either hydraulic pump more than two minutes without requiredfuel in the tank.

WARNING: FUEL TANK IS HAZARDOUS AREA. KNOW PRECAUTIONSBEFORE ENTERING FUEL TANK OR INJURY TO PERSON-NEL AND DAMAGE TO AIRPLANE MAY RESULT.

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HEAT EXCHANGERSYSTEM A

FUEL TANK FLOOR

REAR SPAR OF RIGHT HAND WING

HEAT EXCHANGER HYDR. SYSTEM A SHOWNHEAT EXCHANGER HYDR. SYSTEM B SIMILAR

HEAT EXCHANGER HYDR. SYSTEM B

HYDRAULICCOOLING TUBES

104847

Page: 45Figure 22 System A Heat Exchanger

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29-30 INDICATING (CONT.)SYSTEM A OVERHEAT LIGHT (ABEX PUMP)

PurposeThe electric motor driven pump is monitored for overheat by temperature acti-vated switches in the case return line and in the motor case housing. Theswitches are connected to an amber overheat light above the pump controlswitch.

LocationThe case fluid overheat temperature switch is located below the system AEMDP in the left wheel well.The pump case overheat temperature switch is mounted on the system AEMDP motor housing.

Physical DescriptionThe amber overheat light is powered by dc voltage from the master dim circuit.When case drain fluid temperature exceeds 220F (104C), or pump tempera-ture exceeds 235F (113C), the overheat switches close applying a groundwhich illuminates the overheat master caution and hydraulic annunciator light.When the temperature decreases to 165F (74C), the switches open and theoverheat light goes out.

SYSTEM A OVERHEAT LIGHT (VICKERS PUMP)

PurposeThe electric motor driven pump (EMDP) is monitored for overheat by a temper-ature activated switch in the case return line. The switch is connected to anamber overheat light above the pump control switch.

LocationThe hydraulic drain fluid overheat warning switch is located in the case drainline below the System A EMDP in the left wheel well.

Physical Description/FeaturesThe amber overheat light is powered by dc voltage from the Master Dim circuit.When case drain fluid temperature exceeds 220F (104C), the overheatswitch closes applying a ground which illuminates the overheat master cautionand hydraulic annunciator light. When the temperature decreases to 165F(74C), the switch opens and the overheat light goes out.

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SYS B CASE DRAIN

SYS B EMDP

OVERHEAT SWITCH

SYS A CASE DRAIN

SYS A EMDP

OVERHEAT SWITCH

TEST SWITCHTO MASTERCONTROL CENTER

P6-3 PANEL LOAD

28/16V DC

28/16V DC

C318

C317

MD&T

MD&T

OVERHEAT SWITCH

LIGHT

PUMP OVERHEATSYS A ELEC-2

TEST SWITCHTO MASTER OVERHEAT SWITCH

LIGHTPUMP OVERHEAT

SYS B ELEC-1

1

SYS B ELEC-1PUMP OVERHEAT

LIGHT

OVERHEAT SWITCHTO MASTERTEST SWITCH

SYS A ELEC-2PUMP OVERHEAT

LIGHT

OVERHEAT SWITCH

MD&T

MD&T

C317

C318

28/16V DC

28/16V DC

P6-3 PANEL LOADCONTROL CENTER TO MASTER

TEST SWITCH

SYS A CASE DRAIN

SYS B CASE DRAIN

2

ON ON

ENG 1

OFF

A B

OFF

PRESSURE

LOW

OVERHEAT

PRESSURE

LOW

PRESSURE

LOW

PRESSURE

ELEC 2 ELEC 1 ENG 2

LOW

OVERHEAT

HYD PUMPS

ABEX PUMP VICKERS PUMP1 2 204261a16128

Page: 47Figure 23 Hydraulic Fluid Overheat Warning

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ELECTRIC MOTOR DRIVEN PUMP ACUSTIC FILTER

PurposeThe filter reduces the noise level and vibration of theEMDP.

LocationThe filter is installed in the wheel well adjacent to the pump.

Physical DescriptionThe acoustic filter consists of a housing containing anumber of baffles.

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SYSTEM A EMDP

SYSTEM B EMDP

FWD

WHEEL WELL

KEEL BEAMSEE

SEE

VICKERS EMDPCASE DRAIN LINE

SUPPLY LINE

ACOUSTIC FILTER

PRESSURE LINE

ELECTRICALCONNECTOR

AIRPLANES WITH VICKERS PUMPS

SYSTEM A EMDP SIMILARSYSTEM B EMDP SHOWN

1

2

2

1 CASE DRAIN LINE

PRESSURE LINE

SUPPLY LINE

GROUNDING STRAP

CONNECTORELECTRICAL

ACOUSTIC FILTER

A

A

A

A

ABEX EMDP

767885767898

Page: 49Figure 24 Electric Motor Driven Pump Acustic Filter

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SYSTEM A PRESSURE MODULE

PurposeThe pressure module filters and distributes pump outputs to user systems.

LocationThe module is located on the left forward wall of the main wheel well.

Physical DescriptionThe pressure module consists of a housing containing cartridge-type pressurefilters, pump low pressure warning switches, a pressure relief valve, checkvalves and fittings for attaching system tubing connectors.A non-bypass cartridge-type filter in the pressure line from each pump filtersthe fluid before it is delivered to the using components.It consists of a non-cleanable filter element inside a metal bowl.Check valves are installed downstream of the pressure filters and low pressurewarning switches to isolate them from the output of the opposite pump. Com-ponents can be individually replaced in the module.

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SYSTEM APRESSURE MODULE

PRESSURE MODULEKEEL BEAM

FWD

SYSTEM B

(NOT SHOWN)FROM FLIGHT CONTROL MODULE

TO SYSTEM PRESSURETRANSMITTER

FWD

THRUST REVERSERTO ENGINE NO. 1

EDP CHECK VALVE

TO PTU

EDP LOW PRESSURE SWITCH

EMDP LOW PRESSURE SWITCH

TRANSFER VALVETO LANDING GEAR

FROM EMDP

TO RETURN FILTER MODULEEMDP PRESSURE FILTER

FROM PTU

EMDP CHECK VALVE

EDP PRESSURE FILTER

FROM EDP

THRUSTTO ENGINE NO. 1

TO FLIGHT CONTROL

WHEEL WELL

SELECTOR VALVE ANDSPOILER CONTROL VALVE

MODULE

REVERSER

(NOT SHOWN)

Hydraulic System A Pressure Module shownSystem B Pressure Module similar

(118492)

TO ALTERNATE BRAKE SOURCE

HYDR. SYSTEM PRESS.RELIEF VALVE

Page: 51Figure 25 System A Pressure Module

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Page: 52HAM US/E HAM sp Sep 96

29-30 INDICATING (CONT.)SYSTEM A LOW PRESSURE WARNING

PurposeA low pressure warning system is provided to monitor the output pressure ofeach hydrauliC pump.

LocationIndividual low pressure warning systems for each pump Consist of amber lightson the forward overhead panel and low pressure warning switches in the pres-sure module.

Physical Description/FeaturesThe amber light illuminates when pump delivery pressure is low. The mastercaution lights and the hydraulic annunciator also illuminate for pump low pres-sure.The engine-driven pump low pressure circuit is wired through the engine fireswitch. Pulling the number one engine fire switch disarms the system A en-gine-driven pump low pressure warning circuit.

OperationDuring normal pump operation, the low pressure switches are open and theamber lights remain off. An amber light illuminates when pump delivery pres-sure drops below the preset value of the pressure switch. The setting of theswitches are set by the manufacturer and no adjustments are required.

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Page: 53HAM US/E HAM sp Sep 96 Page: 53Figure 26 System A Low pressure Warning

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PRESSURE INDICATION CIRCUIT - SYSTEM A

PurposeA hydraulic pressure indiCating system is provided to monitor pressure fromhydraulic System A.

LocationThe System A pressure transmitter is located on the forward bulkhead of theleft main wheel well.Airplanes with Engine Instrument System:

System A fluid pressure is displayed on an LED indicator of the SecondaryEngine and Hydraulic Display panel on the Center instrument panel P2.

Airplanes without Engine Instrument System:System A fluid pressure is displayed by the A pointer on the dual pointerremote indicator on the first officers panel (P3).

Physical Description/FeaturesThe pressure indicating system consists of a transmitter and an indicator.Pressure is routed from the common output line of the pressure module to theSystem A pressure transmitter. Pressure changes sensed by a Bourdon tubeare converted to an electric signal by a 28 volt ac synchro.The electric signal is transmitted to a pressure gage located on the SecondaryEngine and Hydraulic Display of the center instrument panel P2 (airplanes withEngine Instrument System)The electric signal is transmitted to a synchro in the indicator which drives thepointer (airplanes without Engine Instrument System).

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HYD SYS PRESS IND (DUAL)

28V ACXFR BUSNO. 2

28V ACXFR BUSNO. 1

TRANSMITTER

TRANSMITTER

REAR POINTER (B)

PRESSURETRANSMITTER

WHEEL WELL

PRESSURETRANSMITTER

FWD

P3 PANEL

P6

SYSTEM ASYSTEM B

FRONT POINTER (A)

SYSTEM B PRESSURE

SYSTEM A PRESSURE

1

1 AIRPLANES WITOUT ENGINE INSTRUMENT SYSTEM

Page: 55Figure 27 Pressure Indicating Circuit

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Page: 56

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2

2 AIRPLANES WITH ENGINE INSTRUMENT SYSTEM

Page: 57Figure 28 Pressure Indicating Circuit

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SYSTEM A RETURN FILTER

PURPOSEThe A system return filter element removes contaminants from the return fluidbefore it enters the reservoir.

LOCATIONThe system A return filter module is located on the left forward bulkhead, ofthe main gear wheel well.

PHYSICAL DESCRIPTIONThe return filter module consists of a filter bowl, replaceable filter element anda filter head.The filter head incorporates a bypass valve, shutoff valve, two check valvesand a differential pressure indicator.When restricted flow causes a pressure drop of 65 psi across the element, thedifferential pressure indicator becomes visible, indicating that the filter is con-taminated and should be replaced.When restricted flow causes an excessive pressure drop of 100 psi across theelement, the bypass valve opens and allows fluid to bypass the filter and flowdirectly into the reservoir.

OPERATIONTwo check valves are installed in the filter head to direct return flow from thesystem through the filter into the system.

MAINTENANCE PRACTICESThe shutoff valve prevents fluid draining from the reservoir when the filter bowlis removed.

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MODULEFOR SYSTEM B

RETURN FILTER

SYSTEM AMODULE FORRETURN FILTER

FILTERMODULE

PORT 2PLUG

PORT 1RETURNFLOW

QADCLAMP

FILTERBOWL

PORT 3TO THERESERVOIR

SYSTEM A FILTER MODULE

DIFFERENTIAL PRESS.INDICATOR (POPOUT)

HYDRAULIC SYSTEM INSTALLATIONMAIN WHEEL WELL

ASEE

A

104843150679

Page: 59Figure 29 System A Return Filter

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Page: 60

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BRAKE

DISCONNECT

VALVE

SELECTOR

PUMP MOTOR

FUEL

AUTOPILOT

AILERONS AND

TRANS

PRESS

SYS

MODULE

PRESSURIZATION

RESERVOIR

CONTROL MODULE

FLIGHT

GAGE

EXCHANGER

SWITCH

SWITCH

EMDP

TRANSMITTER

QUANTITY

RESERVOIR

BRAKES

GROUND SERVICE

TO

RETURN

B

RETURN

B

RETURN

B

FLIGHT

SPOILERS

VALVE

TRANSFER

LANDING GEAR

SPOILERS

GROUND

ALTERNATE

REVERSER

LEFT THRUST

3 AND 6

RETURN

STBY

RUDDER

RETURN

B

AND AUTOPILOT

ELEVATOR FEEL

ELEVATOR AND

RETURN FILTER MODULE

RETURN

TO B

RESERVOIR

FROM B

EDGE DEVICES

TO LEADING

UNIT

POWER TRANSFER

PRESS

B

LANDING GEAR

AND NOSE WHEEL

STEERING

STBY

PRESS

SYSTEM PRESSURE MODULE

PRESS

LOW

HEAT

PRESS

B

PRESS

B

PRESS

B

PRESS

B

PRESS

LOW

EDP

RDV

PRESSURE

AIR

AIRPLANES WITH ENGINE

AIRPLANES WITHOUT ENGINE

INSTRUMENT SYSTEM

INSTRUMENT SYSTEM

SYMBOL DEFINITION

REF FIG. 20 FOR

OFF OFF

TEST

OVHT DET

rE

R

I

F

T

H

V

O

P

O

N

I

OVERHEAT

ENG 1

A

RL

DISCH

T

L

U

A

F

DISCHARGE

APU BOTTLE

INOP

APU DET

FAULT

WELL

WHEEL

NORMAL

B

LOW

ENG 1

OVERHEAT

PRESSURE

LOW

PRESSURE

LOW

PRESSURE

LOW

ELEC 2

A

ON

ELEC 1 ENG 2

PRESSURE

OVERHEAT

ON

BHYD PUMPS

__

____1

PSI X 1000

1

0

4 RFL

SYS A

23

4

F

1

E

HYD QTY4PRESS

3

HYD SYS

2

2

1

1

Page: 61Figure 30 Hydraulic System A Summary

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HYDRAULIC SYSTEM B

PURPOSEHydraulic system B provides fluid under pressure of 3000 psi to portions of theflight controls, landing gear and thrust reverser systems.

SYSTEM DESCRIPTIONSystem B hydraulic power operates the following systems:

- Main Wheel Brakes.- Right Thrust Reverser.- Ailerons - Power Control Unit and Autopilot Actuator.- Elevators - Power Control Unit and Autopilot Actuator.- Elevator Feel.- Rudder.- Flight Spoilers 2 and 7.- Trailing Edge Flaps.- Leading Edge Flaps and Slats.- Alternate Landing Gear Retraction.- Alternate Nose Wheel Steering

SYSTEM B CONTROL AND MONITIRING

General Component LocationsSystem B pressure is provided by one engine-driven pump and one electricmotor driven pump. A 28-volt dc motor operated shutoff valve in the supply linebetween the reservoir and the engine-driven pump is normally open. It isclosed when the number two fire handle is pulled to stop the flow of hydraulicfluid to the engine.

General Subsystem FeaturesBoth pumps are normally operated to output fluid pressurized at 3000 psithrough the pressure module to the using systems. The pressure module con-tains pressure filters, low pressure switches, check valves and a pressure reliefvalve.

Pump Case ReturnCooling and lubricating fluid from both pumps is filtered, manifolded and thenrouted through a heat exchanger in the number two fuel tank before returningto the reservoir.

Return ModuleReturn fluid from the using systems is filtered in the return module before en-tering the reservoir.

Fluid Quantity IndicationFluid quantity in the reservoir is displayed on a mechanical direct reading gageat the reservoir and as a digital readout, in percent of full, on the SecondaryEngine and Hydraulic Display. (Airplanes with Engine Instrument System)Fluid quantity in the reservoir is displayed on a mechanical direct reading gageat the reservoir and on an electric powered remote indicator on the first officerspanel (P3). (Airplanes without Engine Instrument System)

Pump Control and IndicationThe pumps are controlled by individual switches on the pilots forward overheadpanel (P5) The pressure output of the pumps is monitored by individual pres-sure switches in the pressure module. Low pressure detected at the switchturns on an amber low pressure light above the respective pump control switch.The electric motor driven pump is monitored for overheat by a temperatureswitch in the case return line. Excessive temperature turns on the overheatlight above the control switch.The manifolded output of the pressure module is routed to a pressure transmit-ter in the main wheel well. It electrically transmits total system pressure to asystems pressure gage on the Secondary Engine and Hydraulic Display. (Air-planes with Engine Instrument System)The manifolded output of the pressure module is routed to a pressure transmit-ter in the main wheel well. It electrically transmits total system pressure to theB pointer on the hydraulic system pressure gage located on the first officerspanel (P3). (Airplanes without Engine Instrument System)

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Page: 63Figure 31 System B Control and Monitoring

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Page: 64

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HYDRAULIC POWERMAIN

B737-300/400/500

29-10



Page: 65Figure 32 System B Control and Monitoring

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HYDRAULIC POWERMAIN

B737-300/400/500

29-10


SYSTEM B DISTRIBUTION

OperationPressurized fluid from the two system B pumps is manifolded in the pressuremodule and distributed to the main wheel brakes, flight controls and the rightthrust reverser.

BrakesSystem pressure is supplied directly to the brake System and used for normalairplane braking. System A pressure is an alternate method for braking whenSystem B is not available.

Flight ControlsSystem B pressure is provided directly to the trailing edge flaps, leading edgedevices and two 28 volt dc motor operated shutoff valves in the System B flightcontrol module. The spoiler shutoff valve, controlled by the Spoiler B switch onthe flight control panel, is normally open to allow pressure to the outboard flightspoilers (2 and 7).The flight control shutoff valve, controlled by the flight control system B switchon the flight control panel, is normally open to provide pressure to the primaryflight controls, autopilot actuators, and the elevator feel System. A pressureswitch downstream of the valve is actuated by low pressure to illuminate theamber low pressure light below the control switch.

Right Thrust ReverserThe right thrust reverser is powered directly from the right engine driven pumpand via a separate line by manifolded pressure from both pumps through afuse.

Alternate Landing Gear RetractionSystem B pressure is available to the landing gear transfer valve for use as analternate pressure source for gear retraction under certain conditions.

Ground Service DisconnectA ground service disconnect can be used to input pressure downstream of thepressure module from a ground hydraulic cart to operate all system B compo-nents.

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HYDRAULIC POWERMAIN

B737-300/400/500

29-10

Page: 67HAM US/E sp Sep 96 Page: 67Figure 33 System B Distribiution

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HYDRAULIC POWERMAIN

B737-300/400/500

29-10


SYSTEM B HYDRAULIC RESERVOIR

PURPOSEThe B system hydraulic reservoir supplies hydraulic fluid to the B systempumps and the power transfer unit pump.

LOCATIONThe B system reservoir is located in the upper right corner of the main wheelwell, near the forward wall.

PHYSICAL DESCRIPTIONThe B reservoir is an airtight metal shell containing a quantity indicator andports for air pressure, return, a fill line from the standby reservoir, and pumpsupply lines.The engine-driven pump supply line is connected to a standpipe inside the res-ervoir that prevents the use of fluid below the 3.5

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